UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA Bacteriosis (Blight) of the English Walnut in California and Its Control B. A. RUDOLPH BULLETIN 564 DECEMBER, 1933 UNIVERSITY OF CALIFORNIA BERKELEY, CALIFORNIA CONTENTS PAGE Introduction 3 History and geographic distribution of walnut bacteriosis 5 History of the disease in California 6 History and geographic distribution of the disease in other parts of the United States 7 History and geographic distribution of the disease in foreign countries 8 Description of bacteriosis 11 On the shoots 11 On the leaves 15 On the nuts 16 On the catkins 24 Species of Juglans affected by the disease 24 The organism responsible for bacteriosis 27 The effect of desiccation and sunlight on the organism 28 Longevity of the organism in the soil 28 Source of the organism 28 The relation of atmospheric moisture to infection . 29 Probable method of infection 29 Mechanical injuries 30 Insects as carriers of the organism 30 Losses due to bacteriosis in California 31 Control experiments 33 Methods of conducting the experiments 33 The plan of the experiments 33 Where the experiments were conducted 34 How the sprays were applied 35 Spray materials used 35 Spray terminology 35 Methods of determining the extent of control 35 Results obtained experimentally with sprays 36 Bordeaux 8-4-50 the most satisfactory spray for control of bacteriosis 36 The pre-bloom spray 37 Control obtained with bordeaux 8-4-50 as indicated by counts .... 37 Control obtained with one application of bordeaux 8-4-50 as indicated by weights 37 Control obtained with two applications of bordeaux 8-4-50 as indicated by weights 41 Control obtained with multiple sprays of bordeaux 8-4-50 41 Control obtained with bordeaux 8-4-50 as indicated by observations . 44 Discussion 48 Difficulties involved in determining control of bacteriosis 51 Weights alone of good nuts do not tell the extent of control .... 52 Counts alone of diseased nuts do not tell the extent of control .... 52 Control estimates based upon personal observations are not always reliable 57 Cost and profit of spraying 57 The amount of spray needed 58 Typical examples of spray costs and profits 58 How to spray to control bacteriosis 61 Winter sprays 63 The first spray 63 The second spray 66 The third spray 66 The cumulative effect of sprays 67 Reasons why spraying may fail 67 Spray damage 69 The preparation of bordeaux spray 71 List of materials tried with doubtful, limited, or unfavorable results ... 77 Acknowledgments 82 Bibliography 83 Bacteriosis (Blight) of the English Walnut in California and Its Control 1 B. A. EUDOLPH2 INTRODUCTION The present paper is concerned primarily with results obtained in spray- ing experiments for the control of bacteriosis (blight) 3 of the English walnut that have been conducted on a large scale at widely separated points in California since 1927. Walnut bacteriosis is not a new disease. In relation to the history of walnut culture in California it may be considered rather an old one. Be- tween the time when bacteriosis was first observed over forty years ago and the present, much important information about it has been obtained and published. For the sake of clarity, however, as well as to make the control data presented herein easier reading for the grower for whom this paper was written or for the plant pathologist who may never have made a study of the disease, a digest of the known basic facts concerning it has been prepared. It is not in the matter of laboratory studies of the organism that re- search lias lagged but rather in the matter of control. The control of parasitic disease in plants lies chiefly along two lines : the development of immune or highly resistant varieties, and the use of preventive sprays or treatments. Although considerable effort has been expended, no im- mune or even highly resistant variety of English walnut has been found to date. Some so-called "blight-resistant" varieties have been announced from time to time in the past, but none has measured up to the expecta- tions. Their apparent resistance seemingly depends not upon any in- herent physiological properties of the trees but, rather, merely upon the extent to which their new growth escapes rain in the spring as the result of late foliation. The Eureka variety, once acclaimed as highly resistant and even immune to bacteriosis in southern California, is now known to be very susceptible there in occasional years when late spring rains pre- 1 Received for publication November 23, 1932. 2 Associate Plant Pathologist in the Experiment Station. s While the term "bacteriosis" is far more descriptive and definitive than "blight," it is not wholly satisfactory. Crown gall, a bacterial disease of walnuts, is technically a case of true bacteriosis also. As used throughout this paper the term "bacteriosis" refers exclusively to the disease commonly called "walnut blight," "black spot," "black plague" (peste negra), etc., and caused by the attack of the bacterial organism orig- inally named Pseudomonas juglandis by Pierce. [3] 4 University of California — Experiment Station vail. In the damper San Francisco Bay region this variety may be at- tacked severely, and in Oregon it is so very susceptible that it is regarded commercially as a failure and seldom planted. The same is true of many other varieties. Spraying to control bacteriosis has met with little success in the past. This may be due in part to the fact that practically all efforts along this line were made during the winter rather than during the growing sea- son when the disease is active. Until comparatively recent years sprays applied at any time of the year might easily have been unsuccessful, especially upon mature trees, which usually attain huge size, because with older types of spray equipment it was virtually impossible to reach all parts of the trees and spray them properly. Within the past decade power-spraying has undergone great changes for the better, but even today to insure thorough coverage it is still necessary to spray very large trees with specially devised long-range guns from a tower erected on top of the spray rig. In spite of the limitations of the spray machinery of his day, the late Newton B. Pierce, who discovered the cause of the disease and named the organism responsible for it, claimed that applications of bordeaux would reduce infection appreciably. Pierce's reports, written in popular vein and practically devoid of experimental data, were published almost exclusively in several popular magazines which were obtainable only by subscription or purchase. It is not likely that a very large number of walnut growers in California at the time ever saw his articles. In none of his papers does Pierce mention how strong a spray he used, and dis- crepancies exist in his statements as to just when he applied it. In read- ing his reports one cannot help feeling that they are fragmentary and merely forerunners of a complete paper or bulletin in which his experi- mental data would be set down in detail or at least in a more tangible form. Such a bulletin never appeared. Eventually he did publish a tech- nical description of the disease and of the causal organism (42), 4 but in this final report he did not mention spraying at all. . The above criticisms of Pierce's work are not offered. with any inten- tion of disparagement whatever. His laboratory studies still remain the basis of all subsequent work by later workers. They are offered merely as a possible explanation of why this phase of his work, which has been verified by the experiments reported in this paper/failed to make a per- manent impression on the growers of his day. 4 Reference is made in parenthesis to "Bibliography," page 83. Numbers in bold- face or heavy type refer to publications particularly pertinent to the subject under •discussion. ..The publications- in the bibliography deal primarily with walnut bacteri- osis, whereas those cited in footnotes ordinarily- do not. '" BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 5 With the walnut industry firmly established in California and grown to its present considerable proportions it seemed logical to attack the problem of control from the standpoint of sprays rather than from that of resistant varieties, to afford, if possible, some relief to the great num- ber of growers whose orchards are severely affected by bacteriosis. An attempt has been made to have the bibliography given on page 83 as complete as possible up to 1932, when this paper was written. In gen- eral unsigned popular articles in magazines or newspapers which have contributed no original research data or observations have been omitted. HISTORY AND GEOGRAPHIC DISTRIBUTION OF WALNUT BACTERIOSIS THE POSSIBILITY OF ITS BEING OF FRENCH ORIGIN The organism which causes walnut bacteriosis is unable to reproduce or even to live for more than a relatively short period in the soil. Simi- larly it is known to attack only the English walnut and rarely its hybrids. Therefore it seems reasonable to assume that it could not have existed in the absence of walnuts in those localities where it is recognized now, and presumably it was disseminated about the globe on infected stock. Suspicion often has been pointed at France as the source of the dis- ease, and not without reason, since the walnut industry there is an old one, and many of the plantings made throughout the world during the past fifty or sixty years are easily traceable to nuts and scions imported directly from that country. In 1907 C. 0. Smith (62) 5 observed characteristic lesions on scions imported into California from France. When the scions were grafted on black walnut, typical bacteriosis developed on the new growth close to the old wood. No other trees in the vicinity were diseased at the time, and no new shoots other than those from the French scions ever developed bacteriosis. Also, according to C. 0. Smith (51, 53) R. E. Smith saw bac- teriosis in walnut orchards in France in 1913. 6 No French writers have reported walnut bacteriosis in their country, but very recently Wormald and Hamond (107) in England proved con- 's Although the bulletin given as citation 62 was written jointly by several authors, credit for the special section on walnut bacteriosis is given to C. O. Smith. s E. E. Smith was thoroughly familiar with walnut bacteriosis at the time he went abroad and is not likely to have been mistaken in its identity. In personal conversa- tion with me he has described the disease which he saw in France and which beyond all reasonable doubt must have been bacteriosis. However, since no cultures were made, the proof of its identity might be challenged on technical grounds. He saw bac- teriosis in the vicinity of Grenoble, France, and also near Sorrento, Italy. 6 University of California — Experiment Station clusively that it occurs in France. They conducted successful inocula- tion experiments with pure cultures of the organism isolated from dis- eased walnuts growing in the Isere Department, France, and from stem lesions in the same vicinity. Cultural studies showed the organism to be identical with the walnut-blight organism in England and in California. HISTORY OF THE DISEASE IN CALIFORNIA About 1890 the disease was first observed in Los Angeles County on trees which had been obtained from a nursery in Orange County. This nursery is known to have imported walnut trees from France a few years earlier. At practically the same time, or very soon thereafter, the disease appeared in Orange County itself (51, 52, 53, 56, 62). Apparently re- garded as a curiosity at first, bacteriosis became so increasingly destruc- tive in southern California and spread so rapidly to other portions of the state that the United States Department of Agriculture detailed Newton B.Pierce 7 to make a study of it. The progress that Pierce made in his work is suggested in the annual report of the Secretary of the United States Department of Agriculture (25) for 1893. By that time the dis- ease was suspected of being of bacterial origin, but inoculation studies to prove the point had not yet been made. In 1896 Pierce wrote a letter describing bacteriosis to the editor of the California Fruit Grower who published it (37). One may gather from the letter that he had isolated the causal organism and with pure cultures had successfully produced hundreds of artificial infections. He also gave the first really accurate description of the disease that had appeared. In subsequent popular magazine articles Pierce reported its latest geographic distribution and very briefly referred to his control experiments (38, 39, 40, 41). In 1901 he published a technical description of both the causal organ- ism and the disease, referring to the latter as "bacteriosis," as he had done in earlier papers (42) . Around 1900, bacteriosis had become so destructive that the California Walnut Growers Association offered rewards as great as $20,000 for a suitable means of combating it. In 1905 the California State Legislature appropriated $4,000 to the University of California for the study of walnut bacteriosis, and a lab- oratory was opened at Whittier, in Los Angeles County, 8 with A. M. 7 Mr. Pierce's title was Assistant Plant Pathologist, in charge of the Pacific Coast Laboratory of the Division of Vegetable Physiology and Pathology of the United States Department of Agriculture at Santa Ana, California. This laboratory is no longer in existence. « This laboratory is no longer in existence BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 7 West in charge, working under the direction of R. E. Smith. Mr. West confirmed Pierce's identification of the cause of the disease but never published his results. The work was then taken over by li. E. Smith, C. 0. Smith, and H. J. Ramsey (44, 51, 52, 53, 54, 55, 56, 59, 60, 61, 62, 63, 64, 65), who secured and published much data on walnut blight, as well as walnut culture in general. In this work no specific method of control for bacteriosis was developed. From 1913 to 1915, W. S. Ballard of the United States Department of Agriculture conducted spraying experiments in the Vrooman orchard at Santa Rosa. The results were never published. In 1920 Fawcett and Batchelor (23) published results of experiments to control the disease. They found neither a single application of spray very early in the season nor the careful removal of dead wood or infec- tious material from the trees to be effective. In 1926 the California Walnut Growers Association, chiefly at the be- hest of members living in central California, appropriated $2,000 for the further study of the control of bacteriosis, and the writer was placed in charge of the project. The results obtained in the experiments, which were started in the spring of 1927, are given in the present paper. HISTORY AND GEOGRAPHIC DISTRIBUTION OF THE DISEASE IN OTHER PARTS OF THE UNITED STATES Oregon was the second state in the Union to report bacteriosis of wal- nuts when Lewis (31) first described it in 1906. The disease is now recognized in all the walnut-growing districts of that state, and reports of its occurrence and losses occasioned by it have appeared with un- usual frequency (1, 2, 7, 8, 9, 21, 27, 31, 33, 50, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 88, 89, 90, 91, 92, 96, 97, 98) . Bacteriosis was next reported from Texas by Schattenberg (49) in 1908. Later Waite (68), with Schattenberg's paper in mind, 9 referred very briefly to its occurrence there. The descriptions of the disease given by Schattenberg leave doubt as to its identity. Bacteriosis was next reported in Louisiana very briefly by Waite (68) in 1914. McMurran (32) also includes Louisiana in his list of states in which the disease occurs. In 1917, McMurran (32) reported bacteriosis for the first time in Maryland, Pennsylvania, New York, Delaware, Virginia, and the Dis- trict of Columbia, giving credit for the most part to Waite for diagnos- 9 According to a personal letter to me. 8 University of California — Experiment Station ing the disease in specimens received in the government laboratories at Washington, D. C, between the years 1910 and 1916. In 1920, Cook (83) first reported bacteriosis in New Jersey. Two addi- tional reports of its occurrence there have since appeared (17, 85) . Bacteriosis was reported very briefly in 1920 in Alabama (83) and in 1922 in Georgia (85) by the Plant Disease Survey. These are believed to be the only references to the disease in those states. In 1922, Dana (85) very briefly reported bacteriosis in Washington. Since then it has been reported by the Plant Disease Survey (87, 89, 90, 91 ). 10 In 1929, Rosen (78) reported a severe attack of bacteriosis on the leaves of several trees at Fayetteville, Arkansas. In 1930, the Plant Disease Survey (91) briefly reported bacteriosis in Mississippi. HISTORY AND GEOGRAPHIC DISTRIBUTION OF THE DISEASE IN FOREIGN COUNTRIES Reports of bacteriosis in foreign countries are given in the chrono- logical order of their appearance. New Zealand. — In 1900 Boucher (12) reported and briefly described bacteriosis in New Zealand before it was recognized in any other coun- try or any state in the United States outside of California. It occurs at Auckland (12), the Nelson and Takaka districts, at Christchurch, Banks Peninsula, Timaru, Hawke's Bay, New Plymouth, and Tauranga (28, 29), and at Akaroa (5). Russia. — An anonymous writer (4) reported bacteriosis in Russia in 1908. The report states that Jaczewski found the disease to be respon- sible for heavy losses on the Government estate near Sotchi, and Silan- tiev is said to have reported severe losses in Sotchi itself. Sotchi is near the Black Sea in the vicinity of the Caucasus Mountains. No other re- port of the disease in Russia has appeared. Canada. — In 1911, bacteriosis was reported and described in Canada by Giissow (26). It was said to have occasioned severe losses for a num- ber of years in the experimental farms at Agassiz, B. C. The trees orig- inally came from France. No other writer has reported the disease in Canada. Tasmania. — In 1912, bacteriosis was reported in Tasmania by Rod- way (45) . Walnut trees in the vicinity of Hobart were said to be severely affected. No other report of the disease on this island has appeared. io Additional reports of the occurrence of bacteriosis over a widespread area in Washington have been received from Dr. F. D. Heald, Chief of the Division of Plant Pathology, Washington Agricultural Experiment Station at Pullman. BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 9 Mexico. — In 1912, C. 0. Smith (62) reported bacteriosis on walnuts growing along the Pacific Coast of central Mexico. He has made this same report elsewhere (51, 52). Australia. — In 1914, bacteriosis was reported in Australia by Cole (15) who found it in the state of Victoria, where the trees were said to be severely affected at times. The disease is commonly referred to as "black spot" there and elsewhere on the continent. According to Cole, bacteriosis was seen in Australia as early as 1888 by Mr. Brittlebank, Pathologist of the Victoria Department of Agriculture. This is earlier than the first record of it in California by several years. Cole (16) also has reported bacteriosis in the Ardmona, Bright, and adjacent districts of Victoria. Bacteriosis was first reported in the State of South Australia in 1922 by Osborn and Samuel (36), who observed that "during the last twenty years [it had] spread to almost all places in the State where walnuts are grown, even to trees 10 or 12 miles apart from any other." Bacteriosis has been reported as occurring specifically in the Mount Lofty Ranges and in the Auburn district by an anonymous writer (6) . Bacteriosis has been recognized in the State of New South Wales since 1903. It causes most damage in the cooler regions, particularly in the Southern Highlands, according to R. J. Noble of the Department of Agriculture of New South Wales. 11 Chile. — Bacteriosis was reported from Chile in 1917 by Camacho (13). It is commonly known there as the "black plague" (peste negra). In 1926 Capdeville (14) further described the disease and estimated that losses reached as high as 50 per cent at Catemu, Nufioa, and Maruecos. These are the only reports of bacteriosis from South America. South Africa. — Doidge (18) reported bacteriosis of walnut in South Africa in 1918. It was said to occur in practically all parts of the coun- try where walnut's are grown and was believed to have been disseminated on nursery stock originally obtained from France. Also it was believed to have been established in South Africa for some few years previous to its identification there. The disease has been reported specifically from several localities in the Eastern Province, at Eastport, at Clocolan in the Orange Free State, at Potchefstroom in the Transvaal, at Napier in the Bredasdorp District, at Donnybrook in Natal (18, 19, 20) and in the Cango Valley of the Oudtshoorn District (19) . Evans (22) states that bacteriosis was very prevalent in South Africa in 1922. ii Personal letter dated June 10, 1931. 10 University of California — Experiment Station Italy. — Bacteriosis was next reported in Italy in 1923 by Savastano (48). Ferraris (24) also has reported the disease there, giving Savas- tano's paper as his source of information. The disease described by Savastano at great length and attributed by him to Bacterium juglandis Pierce clearly is not the disease under discus- sion, and accordingly, has no place in this paper. 12 It is referred to here, and Savastano's paper is included in the bibliography on page 83, be- cause so many authors include Italy in their reports on the geographical distribution of the disease, giving Savastano as reference. Technically no absolute proof of the presence of walnut bacteriosis in Italy exists. 13 Holland. — Bacteriosis was reported very briefly on walnuts at Zierik- zee, Holland, in 1923 by van Poeteren (67). Experimental data and de- scriptions are lacking. No other report of the disease in Holland has appeared. Switzerland. — Bacteriosis was reported very briefly in Switzerland in 1924 by Muller-Thurgau and Osterwalder (35). Experimental data and a suitable description are lacking. England. — Bacteriosis was reported in England in 1927 by Wormald (69), who isolated the causal organism from leaf spots which developed on very young trees the same year that they were received from a nurs- ery in France and planted at the East Mailing Research Station. Re- ports by Wormald and Hamond of subsequent laboratory studies, in- cluding suitable descriptions and experimental data, have appeared (70,71,72,73,74,94,107). Germany. — Whether bacteriosis actually exists in Germany is not clear from the limited information at hand, but Stapp (66) published a description of it in 1928, which was drawn from California publica- tions, and also a technical description of the causal organism based on Pierce's studies. He refers to the disease as B aid erienb rand der Wal- niisse, but no mention of its occurrence in Germany or elsewhere in Europe is made. France. — The presence of walnut bacteriosis in France has been rec- ognized definitely since 1931. See page 5. ] 2 The disease described by Savastano and referred to by him as the "dry disease" is characterized by a complete desiccation of the tree, all parts being affected, in- cluding roots, trunk, branches, shoots, leaves, and fruit. Affected trees die within a few months to five years after attack. Vague physiological disturbances are noted ; excessive production of fruit which fails to ripen, chlorosis, etc. Black spots appear- on the leaves and nut husks, the shell and kernel may be destroyed. Almost the entire article is devoted to a description of the disease in the roots, trunks, and branches. The black spots on the leaves and fruit, which alone seem sug- gestive of true bacteriosis, are scarcely more than mentioned. Savastano made no cul- tures, conducted no inoculation experiments. !3 See footnote number 6, page 5. BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 11 DESCRIPTION OF BACTERIOSIS Walnut bacteriosis is essentially a disease of the leaves, catkins, nuts, and new tender shoots of the English walnut. It never kills a tree, and, under California conditions, it rarely causes any appreciable defolia- tion even in years favorable to heavy infection. The developing nuts, unfortunately, are very susceptible, which fact alone makes the disease of economic importance. A fine set of nuts at the beginning of the season may be gradually decimated until not a single one remains by harvest time, and yet at close range, the tree itself ordinarily presents no un- usual appearance. In contradistinction to bacteriosis of pears and apples (pear blight, fire blight) 14 caused by Phytomonas amylovorus (Burrill) Bergey et al., or bacteriosis of the filbert (filbert blight), 15 caused by Phytomonas sp., two diseases which attack all parts of their natural hosts, including fruit, leaves, branches, trunks, etc., walnut bacteriosis never attacks wood that is more than one year old. Similarly it never attacks the roots. On the Shoots. — Bacteriosis may be expected to occur on the shoots only during that comparatively short period of a few months after their appearance while they are still green, succulent, and tender. As they toughen and become woody in structure their susceptibility diminishes. The degree to which a shoot is susceptible varies throughout its entire length. Thus the older base of a long shoot may have become fairly woody and correspondingly resistant while the growing tip is still succulent and very susceptible to attack if weather conditions are favorable. By the end of the first season, however, all parts of such shoots will have 14 Recently C. O. Smith successfully inoculated walnut shoots and fruit with the "pear blight" organism. Lesions were produced on both which were indistinguishable from those of true "walnut blight." Natural infection of walnut by the "pear blight organism" is unknown. Smith was unable to infect pear with the "walnut blight" or- ganism. (Smith, C. O., Pathogenicity of Bacillus amylovorus on species of Juglans. Phytopath. 21(2) :219-223. 1 fig. 1931.) ] s Some writers consider filbert blight and walnut bacteriosis to be identical and group the literature pertaining to these two diseases together in their bibliographies. This seems inadvisable in view of the limited information on the filbert disease which has appeared. The two diseases apparently present many characteristics in common, but they dif- fer radically in one point; according to descriptions of it, the filbert disease may produce large cankers on the branches and trunks of the trees, whereas walnut bac- teriosis cannot attack mature first-year wood, let alone the older branches or the trunk. H. P. Barss of the Oregon Agricultural Experiment Station has probably done more work with the filbert disease than anyone else. In none of his papers does he make the positive statement that the two diseases are identical or due to the same organism. In a letter received from him while this paper was being written he defi- nitely states that he prefers to reserve final opinion as to the relationship of the two diseases until more experimental data are available. 12 University of California — Experiment Station matured to such an extent that infection can be brought about only with the greatest difficulty, if at all. Ordinarily infection takes place at or near the extreme tip of the shoot in the tenderest tissue. The entire tip may be killed back for a few inches and in severe cases as much as a foot or even more. But more often the infection is localized and spreads so slowly that the tip of the shoot Fig. l. -Bacteriosis of young green shoots of the English walnut. (Natural size.) grows away from the lesion produced, leaving it farther and farther behind on the shoot. Such lesions may be very small, never attaining a diameter of more than a small fraction of an inch, or the}^ may be sev- eral inches long and extend almost completely around the shoot. Occa- sionally complete girdling takes place, especially when two or more actively spreading lesions coalesce. When girdled the portion of the shoot above the lesion dies as the result of interference with the passage of sap. The lesions may be so superficial as to involve only the bark, or so deep seated that all tissues are destroyed to the pith. It is in the diseased tissue of such lesions that the organism successfully lives over the win- ter (Pierce, 37, 39, 40, 41, 42, 43; C. O.Smith, 54, 62; and others). Bul. 564] Bacteriosis of the English Walnut 13 The first visible appearance of the lesion on the shoot is as a minute, translucent or water-soaked dot, usually about the size of an ordinary pinhead or smaller. As the disease continues to spread the inner or older portion of the spot darkens, eventually becoming black. Surrounding Fig. 2. — Destruction of the terminals of young green walnut shoots by bacteriosis. (Natural size. From Bul. 231.) the black spot may be seen a narrow band of translucent, water-soaked tissue. The width of this band varies according to the toughness and resistance of the tissue itself, as well as the severity of the attack. When the disease is making little progress the band may be scarcely more than visible to the eye, but in young tender tissue with the disease in an ag- gressive state it may vary from one to several millimeters in width. When the disease ceases to be active altogether owing to the toughening of the tissue or to other unfavorable conditions, the band disappears entirely, 14 University of California — Experiment Station and the line between the killed, blackened area and the healthy portion is sharply defined. The margins of lesions, whether active or inactive, are generally very irregular (figs. 1 and 2). As the disease continues to spread in a shoot, the older diseased por- tions dry out and become somewhat shrunken and depressed. This gives the lesion more of the characteristic appearance of a canker. Generally the epidermis in such dead areas cracks as the tissue dries out. Fig. 3. — Lesions on English walnut twigs healing over the year following their production by bacteriosis. The organisms which cause the disease live over the winter in the dead and dying tissue of such cankers as these. (Nat- ural size. Photograph by C. O. Smith.) The dying tissue not infrequently exudes a mixture of decomposed cellular products and bacterial slime, which dries upon the surface as a frosty, whitish, flaky precipitate. With the disease brought to a halt as a result of the toughening and lignification of the tissue, the process of healing sets in. Evidence of callus formation frequently may be seen around the edges of the cank- ers late the same season. Figure 3 shows cankers in the process of heal- ing. Healing is completed in the great majority of instances during the growing season of the year following the attack, and the trees appar- ently are none the worse for their experience. Bul. 564" Bacteriosis of the English Walnut 15 On the Leaves. — All parts of the leaf may be attacked, including the parenchyma tissue of the leaflets, the midribs, lateral veins, veinlets, rachis, and petiole. After infection, minute water-soaked or translucent Fig. 4. — Leaves of English walnut affected with bacteriosis. Note that the tissue of the blade, midrib, or petiole may be affected. (Reduced.) dots appear, which eventually enlarge and darken to a dark brown color as the tissue dies. The margins of such brown spots are a yellowish green in color, lighter than that of the normal healthy tissue adjoining. The individual spots ordinarily never attain a great size and rarely exceed 16 University of California — Experiment Station a few millimeters in diameter. Several smaller spots may coalesce, how- ever, to form a single large one. Typical spots may be circular or irregu- lar in shape. At times infection may be rather severe at the tender margins of young growing leaflets. In this case a considerable killing of the tissue takes place, which results in malformations and deformities as the healthy tissue grows away from the dead areas (fig. 4) . The killing of a rachis or petiole may lead to the death of the leaflet or leaf, respectively, dependent upon it. Defoliation to any appreciable extent is rare, however. In California, sunburn and wind damage may manifest themselves as dead irregular brown spots on the leaflets which might be mistaken for bacteriosis. Such spots, however, are confined almost exclusively to the tender, green parenchymatous tissue between the lateral veins of the leaflets, and they rarely lead to distortions or deformities. The lesions developed on leaves of trees poisoned by excessive amounts of alkali or boron in the soil have been confused by some growers with bacteriosis. On the Nuts. — The nut may be attacked at any time after its first ap- pearance in the spring until it is about ready to drop from the husk in the fall. The period of susceptibility, therefore, is a very long one, which fact constitutes one of the chief obstacles to an easy control of the disease. Blossom-End Infections. — In its earliest stages of development, namely, before, during, or immediately after pollination has taken place, the nut usually is infected at the blossom-end by way of the stigma. The blossom of the walnut is inconspicuous, consisting of two small, greenish to reddish, plume-like lobes at the tip of the tiny young nut. These lobes technically make up the stigma, which is the female repro- ductive process designed to receive the pollen at the time of fertilization (fig. 15, page 64). The surface of the lobes which make up the stigma is very rough and lightly coated with a sticky substance, to insure the retention of any pollen which might fall upon it. This rough, sticky sur- face probably holds the bacteria equally well also. The tissue of the stigma is exceedingly fragile and tender, and constitutionally adapted to easy attack by the organism. After it has become infected the stigma blackens, the first symptom of disease in it being a tiny black spot at its base or a very thin black streak on its side. From the base of the stigma, the disease penetrates the succulent young nut (fig. 5). In California the great loss of crop unquestionably is occasioned by the blossom-end infections. The small diseased nuts, % to % inch in Bul. 564] BACTERIOSIS OF THE ENGLISH WALNUT 17 diameter, are quickly abscissed or shed from the trees, and in years of severe attack the ground may be covered with them. Although the great bulk of nuts affected at the blossom-end drop from the trees while still very small, an appreciable number do not. In those that remain the disease often seems to be temporarily arrested in its progress; the nuts continue to grow and may even reach maturity. It is not unusual, however, for bacteriosis to become active again in them at -Young English walnuts affected with the blossom-end phase of bacteriosis. (Natural size.) a later date and destroy much husk and shell tissue. Or the disease, arrested to all outward appearances, may work inward through the shell at the blossom-end and destroy the kernel wholly or in part. Nuts containing only the blackened, shriveled remnants of kernels destroyed by bacteriosis are not uncommon at harvest and are generally referred to as "blanks." In the packing house they are referred to as "blows." Certain strains of the Mayette, generally regarded as one of the most resistant varieties, show a peculiar susceptibility to bacteriosis at the blossom-end. In certain seasons it may be difficult to find nuts that are not affected. The disease makes little progress outside or inside, how- ever, and is confined to a small spot at the base of the stigma. Some nuts are totally destroyed, of course, but at harvest the bulk of the crop is normal in appearance and presents little or no evidence of having been diseased so generally early in its development. Pollination having taken place, or the period of susceptibility to pol- lination having passed, the stigma quickly shrivels and disappears. In- 18 University of California — Experiment Station fection at the blossom-end then ceases to take place to any great extent, and lateral or side infections become the rule. Lateral Infections. — Lateral infections (fig. 6) may take place at any time after the nuts first appear and frequently accompany blossom- end infections, but they predominate later when the period of pollina- tion has passed. Fig. 6. — Bacteriosis of English walnuts showing lateral infections on the nuts. Note the water-soaked appearance of the tissue at the margins of some of the spots. (Natural size.) Infections on the sides of the nuts, as on the shoots and leaves, are first visible only as minute, translucent or water-soaked dots. As the disease spreads, the older or central portions of the spots darken and finally be- come black. A zone or band of translucent or water-soaked tissue, al- ready described on the shoots, and of similarly varying width, persists during the active spread of the disease and makes a border between the healthy and dying parts. As the lesions enlarge the centers become somewhat shrunken and de- pressed, and not infrequently the epidermis ruptures (fig. 7). After protracted wet weather, and particularly immediately after summer irrigation a black slimy sap (fig. 8) frequently bursts through Bul. 564] Bacteriosis of the English Walnut 19 the epidermis of the lesions. This liquid may be so copious in amount that it collects in great drops and spatters down onto healthy leaves and nuts below. The liquid is swarming with the bacteria that cause the dis- ease and frequently serves as a medium to introduce the organism to Fig. 7. — Advanced stage of bacteriosis of English walnuts. (Natural size.) healthy nuts. Ants, flies, and many other insects are attracted to the juice, and it may be that they too further disseminate the bacteria on their mouth parts and feet. See "Insects as Carriers of the Organism," page 30. The depth of the lesions and the extent to which nuts may be injured by them depends on their age at the time of attack. Nuts attacked at any time before, during, or immediately after the pollination period, almost invariably are completely destroyed or shed from the tree. As the nuts grow larger and shell tissue begins to develop, the disease does not progress as rapidly nor do the nuts fall so readily from the tree. In its earliest developmental stages, the newly formed shell tissue is easily attacked and destroyed, and the developing kernel within, still in the "milk" or "jelly" stage, is likewise quickly rotted to a black, slimy 20 University of California — Experiment Station mass. A little later, when the shell is harder, it may be perforated and the kernel may be destroyed or at least blackened and shriveled to worth- lessness (fig. 9) . Finally the shell attains a toughness which makes it im- penetrable to the bacteria, but some substance, possibly by-products of Fig. 8. — Bacteriosis of English walnuts showing drops of the black, slimy- sap that oozes from the lesions immediately after irrigation or heavy rain storms. (Natural size.) the bacteria or even decomposition products from the decayed husk tis- sue itself, may filter through the shell and produce discoloration or even partial shriveling of that portion of the kernel immediately under the diseased area on the husk. During the last stage of its maturity neither the bacteria nor their by-products can penetrate the shell. At this stage the kernel is not apt to show shriveling or discoloration, but the outside of the shell may be badly stained and the nut rendered a cull because of BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 21 Fig. 9. — Bacteriosis of English walnuts: A, two views of healthy walnut meats in cross section; B, total destruction of the kernel within the shell by the disease ; C, kernels attacked later than in B. They are shriveled, black, and unfit for food. (Natural size.) it. No bleach is sufficiently powerful to remove the stain from the shell without injuring the quality of the kernel. Not infrequently much of the rotten husk tissue clings tenaciously to the shell and makes the nut even more unsightly (fig. 10). The above description is concerned only with the disease in its nat- 22 Univp:rsity of California — Experiment Station ural or uninterrupted progress in infected nuts. There are times, how- ever, when the disease is arrested, and the nut survives the attack. This rarely takes place when the nut is very small, but frequently may be ob- served when it is more mature. In such cases the nut may continue its development but at harvest time show perforations of the shell, de- formity, and other imperfections proportional to the damage done at the time the disease was arrested. Fig. 10. — Stain produced on the shells of English walnuts by bacteriosis which causes the nuts to be graded as culls regardless of the quality of the kernels. Note the decayed husk tissue adhering to the shell of several of the specimens. (Natural size.) Infections taking place very late in the season make slow progress as a rule. Spots of varying size are developed on the husk as usual, but generally they tend to be small. These lesions are more or less confined to the outer tissues of the husk and may not even reach the shell. No dam- age to the nut results from such attacks. Mere blackening or shriveling of a kernel is not always attributable to the effects of bacteriosis. Many other factors, largely physiological, frequently bring either about. Drought may cause shriveling, and sun- burn may cause both darkening and shriveling of the kernels (fig. 11). Sunburn is often mistaken for bacteriosis by growers who have not stud- ied the disease closely. They are easily distinguishable, however. Husk tissue that is severely sunburned is dry and leathery in contradistinc- tion to blighted tissue, which is soft and water-soaked. Also sunburned Bul. 564] Bacteriosis of the English Walnut 23 husk tissue does not cling- to the shell as does tissue affected with blight, There are other dissimilarities but they need not be mentioned here. Improper harvesting and processing methods can utterly ruin the color of both shell and kernel ; to delay husking nuts that have been har- Fig. 11. — Severe sunburn of English walnuts showing the damage done to the husks, shells, and kernels. The circular stripe on the husks and shells is characteristic only of severe burns. (Natural size.) vested may cause the shells to be stained and the skins of otherwise per- fect kernels to turn almost black. Diseased nuts usually fall of their own accord from the tree. Ordi- narily the slightest jar will dislodge them. Occasionally, however, the organism works its way rapidly through the tissue into the stem and kills it before the nut can be shed. In such cases the nut remains hanging 24 University of California — Experiment Station to the branches as a "stick-tight" 1C> indefinitely or, at least, until shaken off by wind storms. Infections at the base of the nut near the stem or on the stem itself easily may lead to the production of stick-tights. Occasionally the disease may pass through the stem of the nut into the base of the twig to which it is attached and cause the development of a small canker there. On the Catkins. — Apparently the catkins are not as susceptible to the disease as the nuts, but under suitable conditions they too may be at- tacked. The disease never develops until after the catkins have broken dormancy and are considerably elongated in the spring. When affected with bacteriosis the individual florets which bear the pollen turn black (fig. 12) and present a somewhat water-soaked and wilted appearance, which contrasts sharply with the green, turgid ap- pearance of healthy florets of the same catkin. A single floret may be affected, or all the florets on one side or at the top or at the bottom of the catkin may show the disease. Similarly the rachis may be attacked at any point along its length. Distortions and deformities in catkins often result from the killing of local areas only (fig. 12). C. 0. Smith (54, 55, 56) has shown that pollen may become infected. It may be that bacteria-laden pollen falling upon the flower parts of the young nuts is responsible for much of the blossom-end infection, but this point has not been proved. SPECIES OF JUGLANS AFFECTED BY THE DISEASE Bacteriosis affects the English (Persian) walnut (Juglans regiah.) almost exclusively, as far as known. According to C. 0. Smith (51, 53, 62), under suitable conditions, the disease may be induced artificially in eastern or American black walnut (Juglans nigra L.), the southern California black (J. calif ornica Wat.), and the northern California black (J. calif ornica Wat. var. hindsii Jepson) by inoculating the ten- der shoots and leaves with the bacteria by the needle-puncture method. In one instance C. 0. Smith (62) noted that bacteriosis had spread nat- urally from artificially infected leaves of northern California black wal- nut to nearby leaves on the tree. The writer occasionally has seen natural infections on the leaves of suckers on California blacks topworked to English varieties which were seriously diseased at the time. Ordinarily, even in nurseries where the disease is apt to affect English walnut seed- lings severely, it is never seen on black stock of any kind. The butternut (Juglans cinerea L.) and the Japanese walnuts (J. is The term "stick-tight" is used also to designate a nut which cannot be sep- arated easily from the husk. Bul. 564] Bacteriosis of the English Walnut 25 sieboldiana Maxim and J. sieboldiana var. cordiformis Makino) may also be infected by the needle-puncture method, according to C. 0. Smith (62). Fig. 12. — Bacteriosis of the catkins of the English walnut. Note the blackening of a local area on the racliis or stem of the catkin on the right. Also note that the healthy florets on the catkins are light in color, the diseased ones are black. (Natural size. Photographed by J. T. Barrett.) C. 0. Smith (41, 53, 62) has found bacteriosis occurring naturally on leaves of Paradox seedlings (a hybrid of the California black walnut and the English walnut) in the nursery, but never on Royal hybrids (a cross between eastern and California black walnuts). But, as indicated above, they may be infected artificially under suitable conditions. Commercial Varieties Affected by Bacteriosis. — There is absolutely 26 University op California — Experiment Station no known variety of the English walnut which is immune to bacteriosis and not many which even show any great resistance. A few varieties do show what appears to be a definite resistance to the disease, but the characteristic is traceable to their peculiar habit of foliating late in the spring rather than to any inherent, physiological properties. Thus, the Franquette, a very late variety, frequently escapes the disease in cen- tral California, where the annual rains are practically over at the time this variety breaks the bud. Farther north, however, in Oregon, where the climate is much damper, the Franquette crop may be wiped out. While all commercial varieties and seedling trees may be regarded as subject to attacks of varying severity according to the climatic condi- tions under which they are grown, the following have been specifically reported as susceptible and discussed in the literature: Bishop (62): Chaberte (73) ; Chase (62, 89) ; Concord (54, 62, 89) ; Ehrhardt (10, 54 55, 56, 85) ; El Monte (33, 62, 98) ; Eureka (1, 10, 23, 54, 55, 56, 89) Franquette (1, 8, 9, 34, 44, 50, 54, 56, 62, 73, 80, 89, 96, 98) ; Gladys (73) Grove (10) ; Mayette (34, 44, 50, 56, 73, 89, 96, 98) ; Meylan (34, 50) Meylannaise (73); Parisienne (73); Payne (10, 64, 65, 89); Placentia (10, 23, 54, 55, 56, 62, 64, 65, 85, 89) ; Pride of Ventura (62) ; Prolific (62); Santa Barbara Soft Shell (62); Santa Rosa (62); seedlings (9, 10, 23, 32, 54, 55, 62, 85, 96, 98) ; Treyve (73) ; Vourey (73). While true physiological resistance in any variety is difficult to recog- nize, it is a very easy matter to see that some individual trees are more susceptible to the disease than others. This applies especially to seedling trees. The degree to which each is affected by bacteriosis varies greatly, but in practically all seedling orchards there is a tree or two so suscep- tible to attack that it is outstanding. Owners not infrequently put iden- tification marks on such trees and on request can readily point them out. It is impossible to recommend any one variety as suitable for general planting everywhere. The grower should select the variety best adapted to his locality, taking into account not only its commercial possibilities there but also its probable degree of resistance to bacteriosis under the climatic conditions which prevail in the vicinity. In a broad way, how- ever, he can be guided in making his choice by the time a variety starts growth in the spring. It would be foolish, for instance, to plant such early varieties as the Santa Barbara Soft Shell, Ware's Prolific, Pla- centia, or Payne in the coastal counties of Oregon where the rainy sea- son persists for months after growth has started in these varieties. From the standpoint of bacteriosis alone these varieties are much more suited to regions farther south, in central or southern California. Many other factors, of course, must be considered in selecting a variety, but a discus- sion of them is beyond the scope of this bulletin. BUL. 5G4] BACTERIOSIS OF THE ENGLISH WALNUT 27 THE ORGANISM RESPONSIBLE FOR BACTERIOSIS Pierce's Description of the Organism. — In his only technical descrip- tion of the organism which causes walnut bacteriosis, Pierce (42) named it Pseudomonas juglandis. In 1905, E. F. Smith (57) changed the name to Bacterium juglandis (Pierce) E. F. S., and in 1930, a committee of the Society of American Bacteriologists 17 reclassified it according to a newer and more modern system calling it specifically Phytomonas jug- landis (Pierce) Bergey et al (11). The following is a verbatim copy of Pierce's original description of the organism and its culture characteristics : Pseudomonas juglandis, n. sp. — A short, rod-shaped microorganism with rounded ends, actively motile, bearing a single long polar usually wavy flagellum. Length of organism, taken from colony in acid gelatin, set directly from walnut, and stained with gentian violet, 1-2 fi, according to whether the germ has just divided or has elongated but not yet divided. Just before separation a pair of germs will usually average about 2 ^ in length. x\verage breadth of organism about 0.5 fi. Occurs singly or in pairs, and sometimes in shorter or longer chains. Produces a bright chrome- yellow growth on potato and many other media. When growing normally on potato the starch is so acted upon by a diastatic ferment produced by the organism, that it is altered throughout a wide band beyond the margin of tlie culture of organisms. This band of converted starch may extend 0.5-1 cm or more beyond the margin of the growth of germs, appears white to the eye, fails to show normal starch reaction to iodine, yields marked grape sugar reactions, has an exceedingly sharp and well de- fined limiting outline, often passing so sharply through a cell as to include only the starch grains on one side of the cell. This broad and distinct ferment band distin- guishes this organism at once from Pseudomonas stewarti and P. hyacinthi, as well as from the more nearly related P. campestris, which occasionally forms a weak but much narrower band, and from all other uniflagellate organisms studied. Organism prefers neutral or acid reaction of culture medium, a moderate degree of alkalinity inhibiting growth; it liquefies neutral and acid gelatin. Produces no gas in fermen- tation tubes of sugar solutions; growth confined to neck and bulb of tube, hence aerobic, no growth under mica plate. Colonies in malic acid potato gelatin and agar circular; at first clear but soon decidedly yellow, margin sharp. This organism is distinguished from P. campestris, the most nearly related species of the genus, aside from the characters already assigned, in producing an abundant and bright yellow pigment on the surface of extracts of the leaves of the following plants, while P. cam- pestris produces little or no pigment upon such extracts: walnut (Juglans regia), magnolia (Magnolia macrophylla), fig (Ficus carica), castor bean (Eicinus commu- nis), loquat (Eriobotrya japonica). Since his paper appeared, several workers in this country and abroad have repeated Pierce's laboratory studies and have verified his findings 17 For a discussion of this newer genus, see: Burkholder, W. H. The genus Phyto- monas. Phytopath. 20(1): 1-23. 1930. 28 University of California — Experiment Station in the main. Doidge (18), C. 0. Smith (62), and Wormald (73) have reported additional laboratory studies of the organism. Bergey (11), Elliott (21), and Stapp (66) have given descriptions of the organism and its culture characteristics, largely based upon the work of Pierce and others. The Effect of Desiccation and Sunlight on the Organism. — C. 0. Smith (62) has shown that the organism can withstand desiccation for as long as seventy-three days when kept in the dark but dies after four days' desiccation in the light. Just how much direct sunlight the organism can stand has not been reported, but it probably will not stand desiccation and direct sunlight in combination for more than an hour, if that long. Longevity of the Organism in the Soil. — No one has reported isolating the organism from the soil itself. Repeated attempts by the writer over a period of years to isolate the bacteria from the soil under badly dis- eased trees have failed. Even moist soil rich in the humus of decayed walnut husks found around packing houses failed to yield the organism. Cultures were made from surface soil and from that taken at different levels to a depth of 18 inches. CO. Smith (54) found that the organism does not survive long when inoculated in either sterilized or unsterilized soil. Cultures made at short intervals indicated a rapid disappearance of the bacteria starting within 24 hours after the time of inoculation. In sterilized soil the or- ganism lived the longest and could be recovered as long as eighteen days after inoculation, but in unsterilized soil, kept at 20° C, it disappeared in from six to nine days. Source of the Organism. — Pierce states in most of his papers that the bacteria live over the winter in the dead tissue of the affected shoots and in the old rotten nuts and leaves on the ground. A number of workers have verified his findings on rotten nuts and diseased twigs but not on the leaves. The work of C. 0. Smith in this connection is particularly pertinent to California conditions. Smith (53, 54, 62) isolated the or- ganism from diseased epidermis, wood, and pith of shoots and from rot- ten nuts hanging in the trees at approximately monthly intervals be- tween the fall and the following spring when the new growth and young nuts had appeared, thus proving such material capable of harboring the organism over the winter. It is the general opinion of investigators — and there seems to be no reason for doubting it — that the living organisms are washed out of the old lesions on the twigs and decayed nuts by the winter and spring rains and spattered onto the susceptible growing shoots, leaves, and nuts. Bul. 564] BACTERIOSIS OF THE ENGLISH WALNUT 29 More recently Miller (98) has isolated the organism from dead buds. C. 0. Smith (53, 54, 55) isolated the organism from the surfaces of healthy leaf and catkin buds in the early spring before growth had started. It is his belief that the organism is commonly disseminated on the healthy buds of scions. He was able to induce little or no infection by inoculating dormant buds even by severe or extreme methods. Leaf buds inoculated when dormant produced healthy foliage in the spring, and catkin buds produced healthy catkins. But inoculations made after the buds had started to grow were increasingly successful according to the stage of development the new growth had reached at the time the inocu- lations were made. The deduction to be drawn from this is that the buds or the new growth from them must reach a certain maturity or stage of development before infection can take place. The Relation of Atmospheric Moisture to Infection. — Probably no outside factor plays so great a role as atmospheric moisture in bringing about infection. That the disease is worse in wet years is universally recognized. Nothing is so conducive to infection as a heavy, protracted rainstorm. But even other forms of precipitation on the susceptible parts such as moisture from fogs, dew, etc., are frequently sufficient to bring about an attack. In California the greatest loss occurs during the wet months of early spring when the nuts are still small. As the long dry season approaches and the rainfall becomes more scanty, infection decreases. After May it may even be negligible. On the other hand, damp summer fogs and mists frequently prevail along the coast and at times penetrate to the interior valleys where walnuts are grown. In their wake late or secondary infec- tions may follow. Probable Method of Infection. — The epidermis of the susceptible parts is possessed of a multitude of breathing pores called stomata, which are capable of being opened or closed by the plant according to its physiological requirements. In dry weather, particularly when water is scarce, the breathing pores are apt to be closed, or nearly so, to pre- vent an excessive loss of moisture. In wet weather, and especially after irrigations, the breathing pores are apt to be wide open to facilitate the passage of excess sap out of the plant tissues. While no one has reported actually seeing the walnut-blight organism enter a breathing pore it is generally accepted that they do. Considering the fact that the organ- isms are motile and able to swim relatively long distances in water it does not seem unreasonable to suppose that many of them find their way through the open pores. Wounds and abrasions also offer a means of easy entrance to the inner tissue. Once within, an ample food supply permits of the multiplication and destructive activities of the parasite. 30 University of California — Experiment Station That the organism can attack the susceptible parts readily through the medium of water is evidenced by the ease with which infections can be induced artificially with it. Bacteria from a pure culture (or the juice expressed from the rotten nuts) when added to water and atomized onto healthy nuts will attack them. Diseased spots may become visible as soon as two or three weeks after atomizing and steadily increase in number until there are hundreds of them on individual nuts at the end of a month. (C. O. Smith, 56, 62, and author's observations.) C. 0. Smith (62) also found that infection was slight when the fruit was atomized in warm sunny weather. This bears out the field observations of many, that infection does not take place so readily during brief, light showers or foggy spells when the water is quickly evaporated from the surface of susceptible parts. Mechanical Injuries. — The simplest, quickest, and surest way to pro- duce bacteriosis experimentally is to dip a needle in a culture of the or- ganism and prick the epidermis of any susceptible part such as the leaves, young shoots, catkins, or nuts with it. The bacteria introduced into the wound quickly multiply, and in about nine days or longer, ac- cording to external conditions, the characteristic rot appears. It stands to reason that any mechanical injury to the susceptible parts such as an abrasion, limb puncture, scratch, etc., may give rise to the disease if by any chance the organism should be introduced into the wound. Many infections clearly take place in this way. Insects as Carriers of the Organism. — C. 0. Smith (62) proved ex- perimentally that insects may carry the germs on their feet and mouth parts, particularly when they have walked through or fed upon the bac- terial exudate which so frequently oozes from the decayed spots. (See fig. 8, p. 20.) To what extent they spread the disease by tracking the organism over healthy susceptible tissue is not known, but it is conceiv- able that some infection follows the spread of the organism in this way, especially in wet weather. Organisms tracked onto dry, uninjured epi- dermis exposed to direct sunlight, probably not only are unable to make an attack but are likely to be killed by the disinfectant action of the sun. The walnut aphid (Chromaphis juglandicola Kalt.) has been sus- pected of disseminating the blight bacteria. The insect confines its at- tacks, however, almost entirely to the leaves, which ordinarily are little affected by the disease. It does not seem probable, therefore, that aphids are responsible for the spread of bacteriosis in the nuts to any great extent. In 1927 an experiment was undertaken to determine whether the dis- ease could be reduced in amount by controlling the walnut aphids. A block of sixteen trees in the Anderson-Barngrover Ranch Company's Bul. 564] BACTERIOSIS OF THE ENGLISH WALNUT 31 orchard at Linden was sprayed for the first time just as the new growth and catkins were beginning to appear, and then at frequent intervals, never exceeding one month, throughout the balance of the season with an insecticide of the following formula : Black Leaf 40 (40 per cent nicotine sulfate) 2 pounds Caustic soda 1 pound Water 200 gallons Additional applications of 2 per cent nicotine dust were given when the balance of the orchard was dusted for aphid control. The control of aphids was excellent in the experimental plot, poor in the trees outside of it. But the crop on the sprayed trees was severely attacked by bae- teriosis regardless of the control of the aphids, and to the eye presented no less disease than that on unsprayed trees. The experiment described is admittedly limited, but the results would seem to indicate that the control of aphids at least does not necessarily effect an appreciable con- trol of the disease. Insects which bite or bore into the young shoots or nuts may enable the disease to get a foothold. Not infrequently bacteriosis starts at holes in the nuts made by the husk maggot and the larvae of the codling moth, two serious pests of the walnut in certain parts of California. LOSSES DUE TO BACTERIOSIS IN CALIFORNIA It is impossible to give the loss occasioned the state of California by bacteriosis in exact figures. All authorities are agreed, however, that the loss of crop due to it far exceeds that of all other walnut diseases put together. Growers' estimates of losses are apt to be too low rather than too high, because usually they are made late in the season when the dis- eased nuts hanging in the trees or lying on the ground are clearly evi- dent to the eye. The greatest loss of crop, however, ordinarily occurs very early in the season when the nuts are still very small. Such affected nuts fall, quickly disappear from sight, and the quantity of them is gen- erally underestimated as a consequence. Only very general estimates and fragmentary observations of sea- sonal losses in the more important walnut districts of California are available. Often these are contradictory. Twenty years ago C. 0. Smith (62) pointed out that although the walnut acreage at that time in south- ern California had multiplied many times during the previous decade, the total walnut crop of the state had not increased during the same period. He attributed this largely to the ever increasing destructivity and spread of bacteriosis. The disease is no less serious today than it was 32 University of California — Experiment Station then, consequently the loss to the state since it was first introduced must have run well into the millions of dollars. C. 0. Smith (62) estimated the average loss occasioned by bacteriosis during the ten years previous to the time he wrote at 50 per cent. He points out that in individual years the crop may be so badly at- tacked that not a single healthy nut remains at harvest. The writer fre- quently has made similar observations. Such losses must be regarded as 100 per cent. On the other hand bacteriosis may be present in some or- chards year after year to no greater extent than necessary to give the crop a desirable thinning. But many orchards likewise are visited year after year by the disease in a distinctly more severe form. One grower in Santa Clara County whose orchard is w T ell known for its fine trees of ma- ture age told the writer that he never yet had learned their full bearing capacity because of the consistent annual losses occasioned by bacteri- osis ever since they had come into bearing. This situation probably pre- vails in many other orchards. Growers in the counties bordering on San Francisco Bay as well as in the interior in San Joaquin County readily agree that in years favor- able to bacteriosis their losses vary from 50 to 80 per cent. In all of these localities the loss may be as little as 10 per cent when climatic conditions are unfavorable to the disease. In Santa Barbara County many orchards have been observed in which the loss could be estimated conservatively at 75 per cent. Mr. Hooper, formerly Walnut Extension Specialist of the University, believes the average loss in this same region over a period of years to be about 25 per cent. Numerous orchards have been visited in Los Angeles County in which the loss could be estimated conservatively at 50 per cent. Observers in Orange, Los Angeles, and other southern counties, are not inclined to regard the average annual loss as high as C. O. Smith did in these same localities twenty years ago. This is not at all improbable, considering the drought that has prevailed for a decade in the state and in southern California in particular. The losses that have been described thus far may be called direct losses. They are concerned merely with the extent to which bacteriosis may destroy the crop in the trees. Indirect losses, less obvious, may be traced to bacteriosis also. Probably no factor has contributed more than bacteriosis to making necessary the complicated routine of the modern walnut packing-house. To separate the good nuts from the diseased (blanks or blows), specially designed vacuum machines must be em- ployed. Also, otherwise good nuts rendered culls because of blight stain Bul. 564] BACTERIOSIS OF THE ENGLISH WALNUT 33 on the shells must be sorted out by hand. To accomplish this the crop must be passed along moving belts in front of workers who examine each nut and remove the blemished ones by hand. The cost of machinery and labor annually employed throughout California in the production of a standard merchantable pack of walnuts free from bacteriosis or its ef- fects is very great. Similarly the cost of converting the blight culls into useful by-products is no small item. CONTROL EXPERIMENTS METHODS OF CONDUCTING THE EXPERIMENTS The Plan of the Experiments. — Because no previous experiments reported in the literature included the application of sprays during the active growing season of the walnut, it was considered advisable to try to effect a control of the disease with spring and summer sprays. Also, since the literature had consistently reported nothing but failure with dormant or winter sprays it was decided to exclude them from the ex- periments, for the time-being at least. Lastly, because the period of sus- ceptibility of the walnut is an exceedingly long one, lasting from the time the nut first appears in the spring until it is ripe and ready to drop from the husk in autumn, it seemed improbable that any spray schedule could succeed that did not include the use of several applications of any given material to the same trees, since no one application of spray or its effects lasts indefinitely. To test out the above ideas a system of moving plots was devised to permit the application of any spray solution to a constant unit of trees in single or multiple applications and in gradually increasing or de- creasing numbers over any given period of time with a minimum of labor and trouble. Figure 13 shows a diagram of a moving plot. According to the plan, 40 trees were sprayed with a given spray solu- tion at definite intervals, but with each additional application of spray the entire plot was moved forward so as to include 10 new unsprayed trees at the front while 10 previously sprayed trees were dropped from the rear. Thus as a result of overlapping, a series of definite, smaller blocks of 10 trees were created which were sprayed one, two, three, and four times each; also blocks of 10 trees, each of which received all sprays but the first, all but the second, and none but the fourth giving a total of 7 blocks of 10 trees each, or a total of 70 trees to each moving plot treated with any one spray material. Check plots of unsprayed trees, never less than 10 in number, in- variably were left at the front and rear end of any moving plot for the 34 University of California — Experiment Station sake of comparison. Also, any one entire moving plot sprayed with a given solution always was separated from another sprayed with a dif- ferent one by at least one row of trees to avoid the possible influence of wind-blown spray from one plot on the other. Usually as many as three rows separated the moving plots and in some instances many more, and these unsprayed trees also served as checks. First spray-Mar. 27-Frui+ nof formed QO GO © O Q Q One Applicaiion Second spray-Apr. 28-Fruit pea size Two Applications Third spray-June 13-Frui+ half-grown Three Fourfh spray-Aug. 4-Fruif full-grown Four Applications Applications Thr Two One Applications Applications Application Fig. 13. — Diagram of a typical moving spray plot. This type of spray plot pos- sesses many advantages in spraying walnut trees experimentally for the control of bacteriosis. Figure 13 shows the spray schedule followed the first year. The first application of spray was made when the buds were bursting and the first new growth had appeared but before any appreciable number of young nuts were exposed. The second application was made when the young nuts had reached the size of peas, the third when the nuts were half-grown, and the fourth when full-grown. In subsequent years va- rious modifications in this schedule were made until a satisfactory one was found. See "How to Spray to Control Bacteriosis," p. 61, for the spray schedule now recommended to growers. Where the Experiments Were Conducted. — The spraying experi- ments were conducted at widely separated points in California on both seedling and budded varieties. Most of the work on budded varieties was done in San Joaquin County near Linden, whereas the work on seed- BlJL. 564] BaCTERIOSIS OF THE ENGLISH WALNUT 35 lings was done largely in southern California in numerous orchards scattered through Santa Barbara, Los Angeles, and Orange counties. Cooperative work with H. P. Barss, Oregon State College, who sought assistance in combating the disease in Oregon, was undertaken the third year of the experiments and certain interesting data were received from him. How the Sprays Were Applied. — The sprayings were made with a modern spray rig of 400-gallon capacity. The rig was equipped with 12-inch iron tires shrunk to the wheels, a feature which made it possible to negotiate soft wet ground in the spring with a full load of spray. An extension tower from the top of which very tall trees could be sprayed effectively was also provided. A constant pressure of 500 pounds was maintained for each applica- tion made except on small trees, when the pressure was reduced to meet the circumstances. For trees of moderate size, ordinary spray guns were used, but for large trees, shade-tree guns and the Spencer walnut- tree gun were frequently employed. No. 8 and No. 9 tips were used in the Spencer guns, but smaller ones (Nos. 6 and 7) may be obtained for work on smaller trees. Spray Materials Used. — Since practically all of the various materials and combinations of materials used in the experiments proved utterly valueless in the control of bacteriosis and often harmful to the trees as well, a detailed discussion of them would be of little value at this point. See the "List of Materials Tried with Doubtful, Limited, or Unfavor- able Results," p. 77. Those materials which gave any appreciable bene- fits are discussed under the section entitled "Results Obtained Experi- mentally with Sprays," p. 36. Spray Terminology. — The following terms have been used to desig- nate the time when the sprays were applied or the size of the nuts when they were sprayed. A "pre-bloom spray" is one applied when the buds are bursting and some of the new growth has developed but when few or none of the nuts have appeared. This stage of development in the trees is referred to as the "pre-bloom stage." A "post-bloom spray" is one ap- plied when the flowers at the ends of the young nuts have faded and turned brown. This stage of development is referred to as the "post- bloom stage." The terms "pea stage" and "olive stage" indicate rather loosely that the young nuts have reached the size of ordinary peas or olives. The terms "half grown" and "full grown" also refer to the size of the developing nuts in the trees. Methods of Determining the Extent of Control. — The extent of the control afforded by the different materials used was determined by : (1) comparing the count of diseased nuts in or under sprayed and un- 36 University of California — Experiment Station sprayed trees; (2) comparing the weight of crop from sprayed and unsprayed trees; (3) estimating the extent of control and determining the general effects of the treatments by making personal observations. None of these methods is without fault in determining the extent of dis- ease control in any economic plant, and each is even more faulty when applied to walnuts. For this reason only control data that show the bene- fits of the spray without the necessity of resorting to statistical methods to prove the point are included in the tables. Wherever possible weights and counts were taken in the same orchard, and in virtually every in- stance the benefits afforded by the spray were sufficient to be readily apparent on sight alone. For a more complete discussion of the problems met with in determining the amount of control see "Difficulties Involved in Determining Control of Bacteriosis," page 51. Quality, trade sizes, and grades were determined after the method of the California Walnut Growers Association. 18 RESULTS OBTAINED EXPERIMENTALLY WITH SPRAYS Even before the season was very far advanced, in the first year of the experiments, it was strikingly evident that control in varying amounts had been obtained with each of three copper-containing materials, namely, bordeaux, basic copper acetate, and ammoniacal copper car- bonate. Bordeaux gave the best results of all, and after several years' trial the basic copper acetate and ammoniacal copper carbonate were dropped from the experiments. See "List of Chemicals and Spray Ma- terials Tried with Doubtful, Limited, or Unfavorable Results," p. 77, for a further discussion of them. Bordeaux 8-4-50 the Most Satisfactory Spray for Control of Bacte- riosis. — Many bordeaux formulas, yielding acid, neutral, and exces- sively alkaline mixtures, were tried in the course of the experiments. The 8-4-50 formula proved superior to all others, and the control data presented in the tables of this paper were derived almost exclusively from experimental use of spray prepared with it. Weaker mixtures pre- is To determine quality at least three random samples of 100 nuts each from each of the sprayed plots were measured and graded for size, also cracked and tested for color, condition of the kernels, etc., and an average taken of the lot. Measurement of sizes invariably was made with the special device used by inspectors of the Associa- tion. The trade sizes are Large, Fancy, and Baby. Jumbo is an extra-large size no longer distinguished from Large by the California Walnut Growers Association. The Diamond grade is the best pack of the California Walnut Growers Associa- tion. The second-grade pack is known as Emerald, and California is third. Since the qualifications of each grade have fluctuated somewhat in the past and may again in the future, no attempt is made here to define them. The grades are based, however, on the color, size, and condition of both shells and kernels. BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 37 pared with ingredients in this same ratio, even bordeaux 4-2-50, often showed distinct control value but were inferior to the stronger spray. In the 8-4-50 formula the lime is cut to one-half the amount of blue- stone used instead of the pound-f or-pound ratio generally employed in making bordeaux spray. The amount of lime used is still distinctly in excess of the amount necessary to neutralize all of the bluestone, how- ever. Several advantages are offered by this formula : the spray is dis- tinctly alkaline, and alkaline bordeaux is less toxic or injurious in its action on tender walnut foliage than the acid or neutral mixture. The addition of more lime than that recommended in no way obviates spray burn of walnut foliage when climatic conditions are conducive to it. See "Spray Burn and Other Undesirable Effects," page 69. Bordeaux of the formula recommended also is of more gelatinous consistency and adheres better than one containing a greater excess of lime, and the spray residue left on the foliage is less opaque and impermeable to light — an important point. Finally its maximum benefits are probably obtained more quickly than when bordeaux with a greater excess of lime is used; certain bordeaux chemists are of the opinion that the greater the excess of lime present the slower the disinfectant action of the spray. No great excess of lime beyond the margin of safety for the average grower is contained in bordeaux 8-4-50. See "The Preparation of Bor- deaux Spray," p. 71, for a simple method of preparing it. The Pre-Bloom Spray. — Because the results first obtained in 1927 and substantiated experimentally every year thereafter clearly showed that the strategic period for securing the maximum control with any one spray is during the pre-bloom stage, attention is called to the fact that a pre-bloom spray invariably was given in each experiment recorded in the various tables and observational data that follow. Control Obtained with Bordeaux 8-4-50 as Indicated by Counts. — In table 1, the figures represent the extent of control obtained with bor- deaux 8-4-50 as indicated by count of diseased and healthy nuts in or under sprayed and unsprayed trees. In several of the orchards two or more applications of spray were given. The counts of diseased nuts in sprayed and unsprayed trees as shown in table 1 indicate a striking control of the disease in most instances. Control Obtained With One Application of Bordeaux 8-4-50 as Indi- cated by Weights. — In table 2 the control obtained with a single spray as indicated by a comparison of weight of crop from sprayed and un- sprayed trees is shown. The spray was applied in the pre-bloom stage. In each experiment cited in table 2 the sprayed and unsprayed plots were immediately contiguous, the trees were of the same size, age, and variety, and were subjected to similar growing conditions. 38 University of California — Experiment Station •c CO pug CO -«t U5 OO •o OO M« © £2 3 a 0> .SP > o> oo CO oo -J* ° » CO CN UJ oo t~> «o © CM CM CM 3 _ 00 oo CO <& CO <© eo CM Ctl to O oq o CM H ocation of the nuts when counted T) T3 fl C 1 c 3 1 1 fl c 3 tJ o co -Q ©CM O to VS ^5-2 o '-° "Bi CM OS CM to o3g Cm" U5 _M co" Hi cd oc i— ( CO Oi Cm" M fl (4 U o fl -2 8 4) 01 ^H a S2 S «s1 m 3 S <1 ^ ■ 4 "1 1 >> "fl •-s DQ T3 / _^_^ x ■M 0) 3 >» - C fl g £ * s s g O oo 8 S 2 cf 2 If ^3 £ » £ « £ « §5 co^ Oh W Pw Ph Pm Ph 0> CM OS o> > -r 00 t 00 *c 13 s a. a X X o> fl _, > 1 fl > i 3 > 1 3 _ >» 8? £ « 03 « 0) u =3 g a "d •>* e 1. "§ s k -S £ -§ 4< 0. oe E tn K t- < GO g 00 e O C o S O oo fl w ^ pq ^ pq t pq C3 ^ 01 £ o C oo ■fl Tf CO o o CM CM tH fl i fc v v v 0> Xi a >> I E-i <1 O 3 CO OO >> M _fl S 4) 73 1 o> ■ <0 .2 3 8 C O 1! fl ^ oj a> fa 5^ >- o oo OS OJ CO CM is 2 O C es 03 g « ™ .2 .5 o* 'S .9 - c J2 >. O O -j 4) ++ III J o O sfl3 fa W 5 .JO oho pq o P4 •-9 o> 6 0> m Sol 01 -rt CO Jii « o t3 fl o pqu- § £ W S °«3 c ^ ■ ■^ !l| -3 .£ a fl g Mils £§ lis ■I— ++^3 Rul. 564 Bacteriosis of the English Walnut 39 _^ <3 s 00 n. 0) 3 s T3 0) b» > >> 3 ,_, IO Ifl !-5 3 1-5 "o3 ., 3 "3 > >> 3 > » bib 1 3 4J h-1 -8 15 A ' N ^— N % 3 >, s g . s rt -!- ^_ V S « 3 o 3 4. O oo o o 3 S 1 a> a» 5 03 M N O r7* £ 1-1 £ « 8 on J5 '53 m M * PL, O Ph Pm Ph C Pm i-i 4« s r- o o 00 > t- ^ Eh >> 3 03 » Q 03 03 03 Q. 03 03 H S § a «< S ^_ O © © «5 "5 "^ CO ■^ -ti >> T ~ T CO OO 00 -a 03 a x a XI 4 X X X V 3 _ > •> ^ -> > ■> 3 ^ > ■> 3 3 3 >> ft m 8 S 7 s ? <5 — o 03 4) 03 o3 03 t-. tj ■*« f . -3 4 c . -d 4< t 1. T3 "H "S ft i- ■ (H 1 u O oo f O oo •e O oo c O o 3 « ^ pq ^ pq ^ PQ PQ pq P u 3 ,0 t^ « > > c ■a rf >> 4> d> 6 ) 4> .2 3 3 3 >> >j 03 03 03 > Ph Ph ! Ph 03 4> © O CM CO CO c CO 03 a> a OS >> ~ 8 a ^ o PQ O « 3 3 .2 o 6 3 IV > . 1? .5 '2 3 tt'l a c .5 l 5 £1 i g g 11 '"is JS 03 m 8 a . 3 a «f O 03 13 «2 O ^ c ) a ;/ S o o o * 3 ■< »-s W o-2 II to J -O 3 o 2^ TS-C 4> tS.2; ft »h -h3-o « ®S 8 •- 40 University of California — Experiment Station TABLE 2 The Extent of Control Obtained With a. Pre-Bloom Spray of Bordeaux 8-4—50 as Indicated by a Comparison of the Net Weights of Nuts from Sprayed and Unsprayed Trees Grower Russel Rowe, Goleta, California Bishop Ranch, Corona del Mar, Plot 1. Goleta, California Bishop Ranch, Corona del Mar, Plot 2. Goleta, California E. U. Leh, Concord, California Mrs. J. G. Miller, Linden, California C. E. Bainbridge, Kenwood, California G. C. Bailey, t Wilbur, Oregon Anderson -Barngrover Ranch Co. Orchard Linden, California Bowman-Kuhn Ranch!, San Jose, California Raymond MillerJ Linden, California Mrs. J. G. Miller,* Linden, California Year 1930 1929 1929 1930 1929 1928 1929 1927 1930 1931 1931 Trees* Variety Seedlings Seedlings Seedlings Payne Payne Concord Franquette Payne Mayette Payne Payne Age Number Old Old Old 5-year grafts on 10-year trees Old 14 years 19 years 7-year grafts on 10-year trees 20 years 16 years 20 years 25 25 Treatment Bordeaux 8-4-50 +H per cent San Jose Sum- mer Oil Unsprayed Bordeaux 8-4-50 Unsprayed Bordeaux 8-4-50 Unsprayed Bordeaux 8-4-50 Unsprayed Acid bordeaux Unsprayed Bordeaux 8-4-50 Unsprayed Bordeaux 8-4-50 Unsprayed Bordeaux 8-4-50 Unsprayed Bordeaux 8-4-50 Unsprayed Bordeaux 8-4-50 Unsprayed Bordeaux 8-4-50 Unsprayed Total yield lbs. 1,183 4,054 3,492 1,182 958 552 351 720 1,020 205 1,326 714 227 169 570 318 761 437 827 588 Average yield per tree lbs. 137 99 169 146 99 53 152 87 138 * The blocks of sprayed and unsprayed trees bracketed together were immediately adjacent to each other, of the same age and variety, and outside of the spray treatment subjected to conditions as identical as it was possible to secure. t Data submitted by H. P. Barss, Oregon State College, Corvallis, Oregon. J A large acreage was sprayed in this orchard with the same results indicated by the smaller n umber of trees in the table. BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 41 A comparison of crop weights from sprayed and unsprayed trees as shown in table 2 indicates a noteworthy control of the disease in most instances with one application of spray. The acid bordeaux which gave the control listed in Mrs. Miller's or- chard at Linden was applied experimentally by the writer. This type of bordeaux is further discussed under the heading, "List of Materials Tried with Limited, Doubtful, or Unfavorable Results," on page 77. Control Obtained with Two Applications of Bordeaux 8-4-50 as In- dicated by Weights. — In the preceding section the results obtained with a single spray applied during the pre-bloom stage are shown. In each case the control has been definite, in many instances striking. In table 3 the cumulative effect of two sprays is shown. In each experi- ment two plots lying side by side received a spray during the pre-bloom stage. Later, as indicated in the table, one of the plots received a second application of the spray at the same strength. At harvest the yield of nuts from each sprayed plot was compared with that from an adjoining block of unsprayed trees. The beneficial effects derived from each indi- vidual application of spray are unmistakable. In table 3 it may be noted that the first spray seemingly effected little control of the disease in Dr. Campbell's orchard. As a matter of fact the control afforded by the first spray was great. The beneficial effects of the first application were gradually lost in this plot, however, when no addi- tional sprays were applied to protect the crop. In table 4 additional figures are given which show the control ob- tained with two sprays. In each case the first spray was given in the pre- bloom stage and the second after the nuts had set. No attempt was made to determine the benefits of each individual spray as was done in the orchards cited in table 3. Control Obtained with Multiple Sprays of Bordeaux 8-4-50. — An at- tempt was made to determine whether multiple sprays, namely, several applications of a given spray to the same trees, would effect a better con- trol of bacteriosis than one spray alone. In table 3 the comparative bene- fits of one and two sprays are shown. Thus far it has been impossible to show in figures the additional value of a third or fourth spray in fighting the disease. This is because the requirements for obtaining comparable results in such an experiment are so exacting that it is practically impos- sible to find them in any one orchard. Fluctuation in the size and general health of the trees as well as in the size of the crop set at different parts of the orchard, the result of uncertain causes, likewise the irregularity with which the disease itself appears, complicate the problem of secur- ing reliable figures to show the relative benefits afforded by more than two sprays. Yet observations made in the course of many experiments 42 University of California — Experiment Station CO < EH o y< o fa 3.8 Qui W GO * W 2 o W 05 Eh * o Q £ w £ w ^ H fa fa Ed % w fa o 03 H o '3 M "cp 0) CP 0) a "2 © CO o CM PH CM ■^ CO CM CO V cp S.at > >>CP "a S Ol CM Oi 3 CO ■* »o o lO CM ■* CO >C CO •** oo o CO 00 ^H 2 '>> o H gt* o « 8 -* «o t* a 00 O •*! CT> t* CO CO •*< CO ■»* 00 o OO CM O c 1 "c3 h c _o "a a 03 £ S3 O S3 S3 03 01 CP bO M 03 c3 OQ "S ss h o o ^ 3 3 S3 » gb m m S3 O S3 S3 O 03

S3 m fin c S3 C O 03 cp cp I 5 ! CO CO MM >, Ph m >> a m o

> -3 3^ S3 o o °° p mm * co O u CP X> s CM CM CM CO OS O CM rl CO CO CO bO • to >> o T3 o "o3 >> 41 'S CO 60 .9 CP 03 02 CO M S3 0) 0) QQ CP S3 >> 03 m u 4) K- 1 OS CM 03 o CO OS CM Q2 CP O "3 a S c3 O .2 © J 1 Q a> "2 H 03 7? «50 CP -5 be T3-QQ •g.2 § 2 T3 S3 S3 O 03 •£ « S3 >>o 03 o 03 Bul. 564] Bacteriosis of the English Walnut 43 £5 ° s « w P O CO EH 8 ft "*3 CO CM V 0> <3 a "2 oo os S H OS 3 ^ a OO «H <* CO "0 CO 2 o "1 ^ lO S rf 00 3 a 1 S SP a -s i I g^ i S o> ■ a m 8 a CD o ft *d co g§ a s § a 3 2 gs Ph >> g a X «J tig =3 ^ ft t- 1 03 O oo fl pq t> 13 X Oi 8? 1 -O Tt< ft g ^ 2 T3 x o) T3 rx ft O ob § P5 P OS OS t>. CO CO OS 01 < CO >> O tH T5 o >> .2 OS > 01 a >> c3 Ph 0) a >> 03 a CO u CM OS © CO 05 CO 03 0) is a 6 O ■2 03 J3 03 g /a O .5 o "3 £ rl > M °3 c - a 1 i Ph . 03 . a o S'-S « Sgi WO 03 03 «- j ^ 2 3-0O rt § i ft o "£ J o ° . 2 O O PP -< a 4) a> ^3 t- u o> o> j- CO «3 M O 0) » | O CO 03 03 *i OQ--' ftl 44 University of California — Experiment Station designed to show the value of multiple sprays frequently seemed to show that each additional application of spray given at the right time afforded a material reduction in the amount of the disease. In the An- derson-Barngrover Kanch Company's orchard at Linden where much work with multiple sprays was done, the relative control of bacteriosis afforded by three and four applications of bordeaux to the same trees appeared to be much greater than that afforded by one or two; there were fewer diseased nuts in or under trees receiving the benefits of nu- merous sprays than in or under those sprayed only once. The great fluc- tuation in the size and general condition of the trees, however, made it impossible to show this difference in figures of any kind. Control Obtained With Bordeaux 8-4-50 as Indicated by Personal Observations. — The following data are almost wholly observational and not often supported by figures. Such data admittedly have the least value of all and have been used here only when striking in character. Much of the information has been presented by growers who were en- thusiastic about the results obtained. In 1928, Mr. D. Chisholm of Windsor, California, sprayed two long rows of old seedling walnut trees which line the entrance drive to his apple orchard with bordeaux 8-4-50 during the pre-bloom stage. Part of the trees were sprayed a second time with the same spray after the nuts had set. All of the trees had been severely attacked by bacteriosis year after year previous to the experiment. Scattered among the apple trees are walnut replants of various ages and sizes. These alone were left unsprayed. When the writer visited the orchard before harvest, the unsprayed trees were so severely attacked by the disease, that the crop was virtually destroyed in all of them. Under one unsprayed tree the entire crop lay rotting on the ground. All of the sprayed trees, on the other hand, bore a splendid crop. The control was visibly greater in the trees sprayed twice than in those sprayed only once. Unfortunately neither weights nor counts were made. Mr. Chisholm enthusiastically expressed his satisfaction with the results obtained. In 1928 and 1929, Mr. Donald Nye of Healdsburg, California, sprayed his sixteen or seventeen-year-old Franquette walnuts with bordeaux 8-4-50 during the pre-bloom stage. An average of only 10 gallons per tree was used, which is a very small quantity for trees of that age. At harvest when the nuts had been shaken down he examined all that lay in a straight strip under the trees. The results are shown in table 5. In 1928, Mr. Nye estimated the crop on the sprayed trees to be three times as great as that on unsprayed trees. Bul. 564] Bacteriosis of the English Walnut 45 In 1929, Mr. Raymond Miller at Linden, California, sprayed a large block of Payne walnuts with bordeaux 8-4-50 during the pre-bloom stage. Mr. Miller's mother, Mrs. J. G. Miller, owns a similar orchard im- mediately across the Waterloo road from her son's. This orchard was not sprayed. Both orchards are about eighteen years of age. In late summer Mr. and Mrs. Miller sent for the writer to observe the extent to which TABLE 5 Extent of Control Obtained in Mr. Donald Nye's Orchard at Healdsburg, California as Indicated by Counts Year Treatment Total nuts counted Per cent diseased 1928 1929 ( Sprayed \ Unsprayed f Sprayed \ Unsprayed 500 500 500 500 2 28 30 43 TABLE 6 Count of Diseased Nuts and Weight of Good Nuts from One Sprayed and One Unsprayed Tree Opposite Each Other in the Orchards Owned by Mrs. J. G. Miller and Mr. Raymond Miller Treatment Stage when treated Count of diseased nuts on ground before harvest Weight of good nuts harvested Net gain in favor of spray Bordeaux 8-4-50+2 per cent Volck oil 9 930 pounds 167 90 pounds 77 Unsprayed the disease had affected the crop in the two orchards. The ground under the unsprayed trees in Mrs. Miller's orchard was literally covered with blighted nuts, whereas under Mr. Miller's sprayed trees the number was negligible. Two trees, opposite each other, one in Mrs. Miller's orchard and the other in Mr. Miller's orchard were selected as representative of the situation in the two orchards. Counts of diseased nuts on the ground under each tree were made before harvest. The weight of crop from each tree was also taken. The results are shown in table 6. In 1930, Mr. J. F. Treat, Jr., in charge of the Hunt Brothers Packing Company's walnut orchard at Linden, sprayed a block of Payne walnuts experimentally. On the way to the Payne trees, the spray rig was stopped to spray one fourteen-year-old Eureka tree in a row of 7 trees. The tree was sprayed first during the pre-bloom stage and again when the nuts 46 University of California — Experiment Station were about the size of peas and the flowers had faded. All trees in the row had been affected severely by the disease in previous years. The con- trol obtained was striking. A count of the blighted nuts on the ground under the 6 unsprayed trees and 1 sprayed tree was made in July. Weights were taken at harvest. The results are shown in table 7. TABLE 7 Count and Weight of Diseased and Healthy Nuts from 1 Sprayed and 6 Unsprayed Trees in the Hunt Brothers Packing Company Orchard at Linden, California, in 1930 Stage when treated Number of trees Count of diseased nuts on ground Weight of nuts harvested Treatment Total Average per tree Total Average per tree Bordeaux 8-4-50 Pre-bloom and post-bloom 1 6 21 1,886 21 318 pounds 253 480 pounds 253 80 TABLE 8 Annual Yield of Nuts in Pounds from 76 Payne Walnut Trees in the Hunt Brothers Orchard Previous to and Including 1930, the Year They Were Sprayed for the First Time Year Treatment Yield Year Treatment Yield 1923 pounds 2,295 3,124 2,759 695 1927 1928 1929 1930 pounds 6,200 1924 3,600 1925 3,639 1926 10,886 In 1930 Mr. Treat also sprayed a block of 76 Payne walnuts in the Hunt Brothers Orchard for the first time. These trees were planted in 1916-1918. Bacteriosis had destroyed much of the crop year after year previous to the time the trees were sprayed. Before harvest, when the writer visited the orchard, there were very few blighted nuts either in the trees or on the ground. The weight of nuts taken at harvest, which practically tripled previous average yields from this block of trees, is shown in table 8. Mr. Treat kindly furnished the yields from the trees over a period of eight years. It will be noted that with the single exception of the crop of 1927, no annual yield was more than a third as great as that the year the trees were sprayed. The year 1927 was the most favorable to walnut produc- tion ever recorded in California. Mr. Arch Wilson of Cupertino, California, who owns an orchard of Bitl. 564] BACTERIOSIS OF THE ENGLISH WALNUT 47 mature walnut trees, reported that bacteriosis had always severely at- tacked his crop prior to his use of spray. In 1930 and 1931 he sprayed with bordeaux 8-4-50 with consequent increase in crop and reduction in the amount of disease. Rows left unsprayed for checks clearly showed more disease than those sprayed. Mr. Frank Leib of San Jose made the following interesting statement after his use of bordeaux 8-4-50 to control bacteriosis : "Overloading of the sprayed trees caused the nuts to be less completely filled but not enough to reduce the grade. To the eye the sprayed trees appeared to have twice as many nuts as the unsprayed trees. Nuts from trees on Royal hybrid root (Bolivian cross) were uniformly well filled, however, and the kernels plump, in contrast to those from trees on California black root." In general Mr. Leib believed the spray to have improved the quality of the nuts, orchard run ; in one of his orchards previous to the year he started spraying he harvested 10 Vi tons net of good-grade nuts and 60 bags of Babies. The first year he sprayed he harvested 24^ tons net of good-grade nuts, and only 18 bags of Babies, from the same orchard. In the orchard referred to above, Mr. Leib has numerous commercial varieties growing. He sprayed all during the pre-bloom stage. By the time he had finished spraying his late varieties, the young nuts in the earlier ones had already passed the pollination period and were ready for the second spray. All varieties were sprayed twice. The Leib and Leib, an excellent variety extensively raised by Leib, had been attacked with increasing severity by bacteriosis for some few years previous to the use of spray. The clearing-up of the disease in this variety during the past two years has been striking. Mr. A. P. Freeman of Lawrence Station, California, has owned an orchard of Santa Barbara Soft Shell Seedlings for twenty-four years. His average annual loss of crop to bacteriosis previous to spraying had been at least 80 per cent. There were years when the entire crop was de- stroyed. Because of the severity of the disease Mr. Freeman long ago removed most of the orchard and planted the ground to other crops. In 1930 he was planning to remove the balance of his trees but decided to spray. He applied bordeaux 8-4-50 during the pre-bloom stage with excellent results. In 1931 he sprayed again, and the writer visited the orchard before harvest. Bacteriosis w r as virtually nonexistent in the heavily loaded trees. Mr. Freeman regarded his control for the two years as practically 100 per cent. Although no trees were left unsprayed for checks, the severe attack on the crop in orchards in the general vicinity clearly showed that conditions there had been favorable to bacteriosis both years. 48 University of California — Experiment Station Mr. Walter Stevens of San Jose in whose orchard counts were made (table 1) in 1930, sprayed again in 1931 with bordeaux 8-4-50. For check trees Mr. Stevens left unsprayed a number of walnut replants of the same variety in an adjoining prune orchard. Unfortunately the age and size of the unsprayed trees varied too greatly to permit of an accu- rate comparison of weights and counts. Some of the unsprayed trees were as large as the sprayed trees, others were smaller, but all set a heavy crop at the beginning of the season. Little disease developed in the sprayed trees throughout the season, whereas the crop in the un- sprayed trees was severely attacked. Shortly before the harvest an in- spection of this orchard showed the ground under the unsprayed trees to be covered with blighted nuts. About 75 per cent of the crop that re- mained on the trees was diseased. The number of rotten nuts under the sprayed trees was negligible. The crop on the trees was excellent and showed very little bacteriosis. Mr. Charles Anderson, in charge of the Anderson Orchard Company's large Payne walnut orchard on Archerdale Road, Linden, California, reported a control of the disease by spraying in 1930 which increased the crop 15 per cent. Mr. Joseph Conner, manager of the Santa Clara Walnut Growers As- sociation packing-house, sprayed some of the earlier varieties in his large orchard near Santa Clara in 1931 with bordeaux 8-4-50 in the pre- bloom stage. He reported a loss of 50 per cent in the unsprayed trees due to bacteriosis, whereas the loss was negligible in those sprayed. Among other growers who have sprayed and reported successful re- sults, often with considerable enthusiasm, may be mentioned Mr. W. H. Ward of Morgan Hill, Mrs. Glen Allen of Santa Clara, Mr. Galen Rich- ardson of Byron, Mr. O. L. Freisinn of Santa Rosa, and Mrs. A. M. Moore of Ventura, all in California. DISCUSSION The prime object of the experiments has been to determine at what time or stage in the annual growth cycle of the walnut, sprays might be expected to control bacteriosis. Data showing the successful results ob- tained with sprays have been presented in the preceding section. It has been upon the accumulation of such data, as well as the writer's personal observations and experience, that the spray schedule recommended later on in this paper is based. It hardly seems necessary in a paper of this kind to present the accumulation of data, unsuccessful in character, which was obtained along with the successful. Much of it was obtained, however, and some of it has been used throughout the paper when neces- sary to the proper presentation and interpretation of successful results. Bul. 564] BACTERIOSIS OF THE ENGLISH WALNUT 49 Experimental data obtained over a period of six years seem sufficient to justify the conclusion that the pre-bloom spray is absolutely indis- pensable and that its omission is almost certain to result in failure. In only one year were the climatic conditions in the locality where the ex- periments were being conducted such that the omission of the pre-bloom spray was not accompanied by untoward results. Thus the circumstances under which this spray can be safely dropped from any spray schedule recur so infrequently that it would be very unwise to chance omitting it. While best results ordinarily were obtained when the first application of spray was given during the pre-bloom stage as defined on page 35, there were exceptions to this rule; occasionally excellent controls were ob- tained slightly earlier, namely, when the buds were merely swelling and very little new growth had appeared; or even a little later, namely, when the young nuts not only had appeared but when some of them al- ready had reached the size of peas. Control at this late date was very exceptional, however, and it may be expected to occur only when the climatic conditions preceding the application of the spray have been distinctly dry and unfavorable to infection. Spray applied at this stage also may interfere with fertilization of the nuts. It has been shown in table 2 that the control exerted by a pre-bloom spray may persist, in part at least, until harvest. It may be stated frankly, however, that such results were the exception rather than the rule. It seems unnecessary to present data showing how a single pre- bloom spray may fail to control walnut bacteriosis. The dictates of com- mon sense and a simple knowledge of the disease with its very long in- fectious period make it clear that an adequate control with a single pre- bloom spray ordinarily must be the exception rather than the rule. Negative data bearing on this point also might be misinterpreted; it might reasonably be questioned whether the failure was traceable to the unsuitability of bordeaux as a disinfectant to control bacteriosis or sim- ply to insufficient applications of the spray. Data from the Campbell orchard (table 3) were included purposely to prove the latter to be true. It is impossible to state how long the protective action of any one ap- plication of spray will last. The strength of the spray, its method of prep- aration, the climatic conditions, and the rate of growth of the suscep- tible tissues very definitely influence this point. In tables 3 and 4 the benefits afforded by two applications of spray have been shown. It is impossible to secure figures that prove irrefutably that a second spray applied immediately after the nuts have set will nearly always produce greater benefits than one applied late — a month later for instance. But the experimental data and personal observations 50 University of California — Experiment Station strongly indicate this to be a fact. There may be exceptions. The crop in- crease resulting from a second application of spray in July to trees in the Bowman-Kuhn orchard (table 3) was as great as that in the Bishop orchard which was sprayed for a second time at a much earlier date. But this alone cannot be interpreted as proof that long intervals between sprays lead to as good results as short ones. On the contrary the relative increase in the Bowman-Kuhn orchard was less owing to the delay than in other orchards sprayed earlier but in which the yields were smaller for reasons other than bacteriosis. The Bowman-Kuhn ranch is well known in the Santa Clara Valley for its heavy yields, and the year of the experiment the crop was extraordinarily large. In spite of heavy losses by bacteriosis a large amount of the crop had not yet contracted the dis- ease at the time the second spray was applied and was protected by it. Abnormally damp weather later in the season rather than early greatly influenced the situation in the Bowman-Kuhn orchard also. Climatic conditions vary somewhat from year to year. Occasionally the deviation from the normal is extreme; in an abnormally dry year a delay in the application of the second spray after the nuts have set may produce no unfavorable results. But since there is no way of knowing when such extremes may occur it would be folly to risk the delay. As indicated in the preceding section it has not been possible to show with figures the relative value of a third or fourth application of spray to control bacteriosis. Observational data confirming their value is abun- dant, however. For instance, in 1929 the Visalia Orchard Company's orchard (table 4) was given a pre-bloom and a post-bloom spray. In June, before the abnormally late rainfall of that year took place, there was an almost perfect control of the disease in the very large crop in the sprayed trees. The number of blighted nuts either in or under the trees was negligible. The crop in the unsprayed trees left as checks was se- verely attacked, and the ground beneath was covered with rotten nuts. After the June rains bacteriosis quickly established itself in the sprayed trees, which at that time were without protection since the spray residue applied two months earlier had largely been dissipated or outgrown. By harvest much of the crop had been destroyed. A third spray applied be- fore the June rains very likely would have prevented much of the in- fection that took place so late that year. Ordinarily sprays applied as late as June will be of little value be- cause under normal conditions the rainy season in California will have been passed and the disease automatically checked as a consequence. Evi- dence of the kind given seems to justify the recommendation of suffi- cient sprays during the wet season to give the crop adequate protection. BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 51 DIFFICULTIES INVOLVED IN DETERMINING CONTROL OF BACTERIOSIS There is no single, simple, and exact method of determining the extent of control of bacteriosis obtained with sprays. Numerous obstacles are encountered for which due allowance must be made if the results secured are to be properly understood. Outbreaks of bacteriosis occur only when all of a number of condi- tions are favorable, consequently its occurrence is very irregular from season to season. Similarly the severity of the attack in the same locality may vary from orchard to orchard and even within one orchard. Hard and fast conclusions for or against a given treatment cannot be drawn from figures taken at widely scattered points in the same orchard. Fluc- tuation in the general size of the trees, particularly in large blocks, further adds to the difficulty of demonstrating with simple figures the indubitable fact that two sprays may give better results than one, three better than two, etc. In contradistinction to the apricot, peach, and many other economic crops, walnuts are never thinned to produce uniformity of size and qual- ity. The custom is to leave any and all nuts on a tree that it can produce. Up to a certain point, which will vary greatly with the vigor of the tree, the available moisture, the general environmental conditions, etc., it will- produce the superior quality demanded by the trade, but beyond the optimum quantity for that tree under its environmental conditions, the quality and size become increasingly less satisfactory. This situation becomes all the more complicated in seedling trees, no two of which are just alike in their yield characteristics; some are always shy bearers while others regularly produce huge crops. Some produce small sizes only. Still others produce kernels of inferior quality regardless of the environment. To crowd more nuts on such trees beyond their optimum simply means the lowering of an already low standard of size or quality or both to a point which is unsatisfactory from the standpoint of the trade. A single example will serve to illustrate the point : In one or- chard the crop set in 1927 was excessive. At harvest the nuts were highly unsatisfactory; the size was small, the average run of the orchard con- sisting of 50 per cent Babies. Jumbos were absent and there were ex- ceedingly few Large-sized nuts. The great bulk of the larger nuts was, rather, of merely a poor Fancy size. To make the Diamond grade with such a product necessitated the employment of extreme methods in the packing-house, namely, exceedingly careful sorting by hand and vacuum machine and finally blending the nuts with better ones from other or- 52 University op California — Experiment Station chards. The following year the crop in this same orchard was thinned by frost. At harvest the average size and quality of the nuts were excep- tionally fine; a high percentage of Jumbos prevailed and the Large size constituted the bulk of the crop. Babies were almost totally absent. The kernels were well filled, and the entire orchard run was of Diamond grade. Bacteriosis often acts like frost and may be a blessing in disguise when trees are overloaded or environmental conditions are unsuited to the production of large crops. Unfortunately the disease usually thins the crop too much. But to protect the crop on overloaded trees from bac- teriosis by sprays simply means a crop of nuts of inferior size and qual- ity at harvest. Some growers have erroneously attributed such inferior- ity to poisonous effects of the spray. When not loaded beyond their op- timum, sprayed trees produce nuts of satisfactory size and quality. Weights Alone of Good Nuts Do Not Tell the Extent of Control. — Trees sprayed with bordeaux may present an unmistakably larger crop to the eye than those not sprayed and yet at harvest produce a very dis- appointing weight of nuts. In some instances no gain by weight will have been made at all. A careful measurement of the sizes and a crack test frequently will tell that part of the story not revealed by the weights; the extra nuts are there, but they are smaller in size, and per- haps inferior in quality also, as a result of overloading the trees. In cer- 'tain tests made, sprayed trees yielded twice as many Babies and dis- tinctly fewer Large nuts than unsprayed trees with crop thinned by bacteriosis. It is when the disease proves particularly severe and cuts the crop badly on the unsprayed trees that the weight of the crop on sprayed trees, regardless of the size or quality of the nuts, may and frequently does show the real protective value of the spray. Figures covering such unmistakable control by weight are given in tables 2 and 3 (pages 40 and 42, respectively). Counts Alone of Diseased Nuts Do Not Tell the Extent of Control. — Counts made of diseased nuts in or under sprayed and unsprayed trees may be very misleading when unsupported by other data. It is easy to count the diseased nuts lying on the ground, less easy to count them while they are still hanging in the trees, because they are not so easy to see and many may be overlooked, thus leading to incor- rect conclusions. When the count of diseased nuts lying on the ground under un- sprayed trees or hanging in them is vastly greater than that made in or under sprayed trees, as is often the case, there can be no doubt as to the BUL. 564] BaCTERIOSIS OF THE ENGLISH WALNUT 53 protective value of the spray. The difference in the weights of the crop will usually substantiate the proof obtained with counts. At times, however, the weight of crop from sprayed and unsprayed trees may not show the great difference that the count of diseased nuts in or under the trees seemed to forecast. This puzzling fact may be ex- plained in part on the grounds that severe infection of the crop may have taken place after the count was made and much of the crop de- stroyed. A count merely indicates the amount of disease visible at the time it is made. In 1929, for example, the loss in the Linden area was largely due to late infections which followed one of the wettest Junes ever recorded there by the United States Weather Bureau. Counts made in one orchard before the rains showed little disease in either the sprayed or unsprayed trees, but counts made after the rains showed a severe infection of the unsprayed nuts. At harvest results were considerably different than anticipated on the basis of counts made before the rains. Most counts of diseased nuts are made only after they are large enough to be discerned readily on the ground or recognized in the trees. Such counts cannot and do not reveal the loss of very small nuts early in the season. Theoretically the loss of very small nuts affected with the disease should be less from sprayed trees than from unsprayed. Accordingly it is reasonable to suppose that the weight of good nuts at harvest from sprayed trees would be even greater than percentage estimates based on counts made fairly late in the season would seem to forecast. Actually this seldom proves true; the factor of overloading usually enters and causes the nuts to be smaller and less filled so that there is ordinarily no more gain in weight than the counts would indicate. On the other hand, unsprayed trees with crop materially thinned by the disease early in the season may and frequently do produce larger and heavier nuts and as a consequence may yield almost as much by weight as sprayed trees. But if the disease has been very severe in the unsprayed trees the high count of diseased nuts will indicate a loss that will also show in the weights regardless of size or quality. If large canvases were placed upon the ground under the sprayed and unsprayed trees at the very beginning of the season and counts of the diseased nuts that fell made at short intervals until harvest, a more ac- curate estimate of losses could be made. The difficulties involved make such an experiment impractical. Similarly, if all the healthy and dis- eased nuts in the sprayed and unsprayed trees were counted, the exact percentage of loss due to the disease could be determined, but the job would be an exceedingly laborious one. 54 University of California — Experiment Station Counting the diseased and healthy nuts in certain areas or at certain levels in the trees or on a given number of limbs is apt to lead to incor- rect conclusions unless the work is done on a very large scale, because the disease often appears unevenly in the trees; it is usually worse at the lower, damper levels and on the north or cooler sides of the tree, but not always. It is not always easy to secure satisfactory weights and counts in the same orchard; the method of irrigating orchards often precludes making accurate counts of the diseased nuts on the ground, as does the presence of weeds in orchards left uncultivated until harvest. In table 9, however, may be seen a striking control based on weights and counts in old seed- ling trees. Counts were made of all diseased and healthy nuts hanging in the trees which could be seen clearly within 15 feet of the ground. The plots were immediately adjacent to each other. TABLE 9 Counts and Weights of Diseased and Healthy Nuts from the Same Plots of Sprayed and Unsprayed Trees at the Bishop Ranch, Goleta, California, in 1930 Control as shown by counts Treatment Number of trees in plot Total nuts counted Number of diseased nuts Per cent of diseased nuts 10 10 2,900 3,563 138 1,618 4 75 45.41 Control as shown by weights Treatment Number of trees in plot Total yield good nuts Average yield per tree, good nuts 10 26t pounds 644 988 pounds 64.4 34.5 * The unsprayed trees not only were larger than the sprayed trees but were in a better physical con- dition, having less heart rot, dieback, etc., thus throwing the burden of proof sharply on the figures ob- tained with the spray. The plots were immediately contiguous. t Whereas the weight of the crop was taken from the 26 unsprayed trees, counts were made in only 10 of these same trees. To make counts carefully is a slow process and the smaller number of trees, typical of the block, was considered sufficient. Similar results may be noted in tables 1, 2, and 3, which contain counts and weights, some of which were compiled in the same orchards. There are other serious obstacles to a correct determination of crop yields on the basis of counts of diseased nuts alone; sprays applied at the wrong time may interfere with pollination and cause a heavy drop of the young nuts. Similarly improperly made spray may burn the nuts and cause many of them to fall. Trees with crop thinned as the result of either Bul. 564] BaCTERIOSIS OF THE ENGLISH WALNUT 55 or both may show very little disease indeed when counts are made, and yet at harvest yield a weight of nuts that is very disappointing. For in- stance a count of several thousand nuts made in unsprayed trees may show 20 per cent to be diseased. A similar count in sprayed trees may show only 10 per cent. But if 15 per cent of the crop was destroyed at the beginning of the season on the sprayed trees as the result of spray burn or interference with pollination by the spray, then the weights of crop at harvest may be less than that from the unsprayed trees in spite of the control of the disease. Examples can be given : In Oregon the or- chards of R. Forbis at Dilley and J. 0. Holt at Eugene showed a note- worthy control of the disease on the basis of counts alone (see table 1, p. 38). At harvest, however, the average yield per tree by weight was very much less than that from unsprayed trees. In the Holt orchard the sprayed trees averaged only 22 pounds, the unsprayed 41 pounds. The trees were sprayed twice, the second spray having been applied when the nuts were about the size of peas, a stage now known to coincide roughly with the period of fertilization. The spray also severely burned the trees according to H. P. Barss, who cooperated in this experiment. In the writer's opinion the apparent control of the disease indicated by counts and the loss of crop indicated by weights may be explained on the basis of spray burn or the interference with pollination by the spray, or both. Very serious spray burn also was reported in the Forbis or- chard, which may have been responsible for the similar situation there. In 1929 certain blocks of seventeen-year-old Payne walnut trees in the Anderson Orchard Company's orchard at Linden were sprayed ex- perimentally during the pollination period. A heavy drop of small nuts followed. The remaining nuts developed very little disease. In midsum- mer the count of diseased nuts under the sprayed trees averaged 24, under the unsprayed trees 300. Mr. Charles Anderson, in charge of the orchard, made a count at a different period and found 500 diseased nuts under one unsprayed tree, 8 under an adjoining sprayed tree. At har- vest, however, the sprayed trees yielded a smaller crop by weight than the unsprayed trees in spite of the severe attack of the disease in the latter. Interference with fertilization by the spray applied at the wrong time and consequent heavy drop of nuts is the probable explanation of the results obtained. A crack test of the crop thinned by spray may show a distinctly im- proved size and quality. This was true in the Anderson orchard just re- ferred to where the unsprayed trees were overloaded to begin with and not appreciably thinned by the disease until late in the season. Thus the nuts lost by spray injury may have been numerically greater than indi- cated by weight alone. 56 University of California — Experiment Station Weights of nuts from sprayed and unsprayed trees are concerned with quantity and tell little or nothing about the quality. Counts on the other hand are very untrustworthy as an index of quantity, but in mak- ing them a clue often may be revealed as to what the quality of the nuts will be ; nuts infected very late usually are not destroyed, but they do not often escape being shell-stained, and stain throws them at once into culls, the lowest-priced merchandise. A count of the spotted nuts made late in the season will give some idea as to wiiether much of the crop will be shell-stained or not. For instance in the Anderson Orchard Com- TABLE 10 Yield of Shelled-Stained Nuts from Sprayed and Unsprayed Trees in the Anderson Orchard Company's Orchard at Linden, in 1929 Number of trees in plot Total nuts harvested in plot Weight of shell-stained nuts Treatment Total in plot Average yield per tree Wet weight Dry weight 11 28 pounds 1,867 4,268 pounds 255 85 pounds 23+ 3 pounds m 2} pany's orchard just referred to where the weight of nuts from un- sprayed trees exceeded that of the sprayed it took four men working at top speed to pick the shell-stained nuts from the belt as they came through the vacuum machine and huller. It was one lazy-man's job to pick the few shell-stained nuts from the sprayed plot when they came through. Table 10 gives the figures obtained in the experiment. In table 10 an allowance of 20 per cent for shrinkage in dehydrating has been made. Shell-stained nuts averaged 16 pounds per tree less in the sprayed plot than in the unsprayed. Shell-stained walnuts were worth 8 cents a pound that year at the cracking plant of the California Walnut Growers Association. The 16 pounds therefore were worth only $1.28. If they had been protected against the disease they would have brought about 20 cents a pound, 19 which was the average price for good Payne nuts, orchard run in that year, or $3.20 for the 16 pounds. Thus, there was a loss of $1.92 a tree due to stained shells alone. It cost between 70 and 80 cents a tree to make and apply the spray. A net gain of $1.12 to $1.22 a tree could have been realized on the basis of reduction of shell- staining alone. 19 The prices for Payne walnuts, orchard run, for 1931 and 1932, which are the lowest ever set by the Association for this variety, would be less than the 20 cents average given above. Incidentally the culls would be worth less also. BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 57 Control Estimates Based Upon Personal Observations Are Not Al- ways Reliable. — Control estimates made by merely looking at the trees are very untrustworthy when unsupported by other data such as weights and counts. Only when the control of bacteriosis in sprayed trees is extreme can one be reasonably sure that it has occurred at all or that proof will be found in increased weights at harvest. An increase in numbers is more apparent to the eye than the slight decrease in size of the nuts and plumpness of the kernels which frequently result when trees are over- loaded, factors which may influence the weights unfavorably. On the other hand weights taken at harvest may reveal a certain amount of control by spray not appreciable to the eye when the crop is on the trees. COST AND PROFIT OF SPRAYING In tables 2, 3, 4, 6, and 7 the net gain in weight of nuts obtained by spraying has been shown. The question at once arises as to how much it costs for materials, labor, etc., to get the nuts. In short, does it pay to spray ? Bordeaux 8-4-50 is made of bluestone, lime, and water. Its prepara- tion is discussed further on page 71. The prices of bluestone and lime fluctuate both with the year and with the locality in which it is pur- chased; they are higher in some years and in some localities than in others. Bluestone costs from 6 to 6% cents a pound in barrel lots (552 pounds). Good lime may be had from % to 2 cents a pound in barrel lots (180 pounds). One gallon of bordeaux 8-4-50 at top prices costs a little more than 1 cent. The cost of applying the spray varies greatly. It is cheaper in the long run to own one's spray equipment, particularly if the orchard is a large one. It is absolutely imperative to get the spray on at the right time if the best results are to be obtained. This is not always possible when the spray equipment must be rented. The prices charged by professional sprayers who furnish all necessary equipment and labor but not the spray material vary greatly according to the requirements of the work and the way the contract is drawn up. Ordinarily it costs from % to l 1 /^ cents a gallon to have the spray applied. These prices naturally include the sprayer's profit. For average working purposes the writer estimates the cost of mate- rials at 1 cent a gallon and the cost of applying the spray at 1 cent a gallon, or a total of 2 cents for each gallon of spray applied. 20 20 The average prices quoted above for labor and raw materials are considerably higher than those prevailing in 1931, 1932, and 1933. Bluestone could be had in large lots in some localities in 1932 and 1933 for one-half the price given above. The cost of a gallon of spray was less than 1 cent in 1931 and still less in 1932 and 1933. 58 University of California — Experiment Station The Amount of Spray Needed. — All parts of the tree must be thor- oughly drenched with the spray. A mist or light fog which merely dam- pens the twigs and nuts will not do. A tree may be considered well sprayed only when all parts of it, inside and out, including the wood, foliage, and nuts, shine mirror-like in the sunlight. Unsprayed portions of the tree have a dull appearance in contrast. Excess spray that runs off is wasted. Typical Examples of Spray Costs and Profits. — In table 11 typical examples of spray costs and profits realized by individual growers of TABLE 11 Cost and Profit of Spraying in Individual Orchards Orchard Bainbridge Visalia Orchard Company Anderson - Barngro- ver Ranch Com- pany Orchard J. G. Miller J. G. Miller Bowman-Kuhn Orchard 1928 1929 1927 1929 1930 1929 Complete data in table No. 1, 2 4 Number of appli- cations of spray given 1 1 1 / 1 \ 2 Total spray applied per tree Amount Cost gallons 15 dollars 30 0.80 20 0.50 0.60 0.36 1.26 Increase in yield per tree Weight Value pounds 20 dollars 4.00 1.20 4.00 6.60 4.80 7.20 Net gain per tree from spraying dollars 3.70 3.00 1.00 3.50 6.00 4.44 5.94 Payne and Concord walnuts are given. Profits have been computed on a basis of 20 cents per pound, orchard run, for good nuts of these varie- ties. 21 Cost of the spray has been estimated on a basis of 2 cents per gal- lon applied. Mr. R. E. Barrett, entomologist of the Saticoy Walnut Growers Asso- ciation, has submitted additional cost and profit data which he secured experimentally in three different orchards in Ventura County, Califor- nia, in 1932. See table 12. Cost of making and applying the spray was 1% cents a gallon. Profits have been computed on a basis of 10 cents a pound for the walnuts, orchard run. In a third orchard Mr. Barrett secured additional cost and profit data. See table 13. The net profits indicated in tables 11, 12, and 13 are real or absolute only as far as the size and quality of the nuts were not impaired as the result of increasing the crop. An increase in quantity to the point of 2i This estimate furnished by officials of the California Walnut Growers Associa- tion is the average price of a great many years. The price may be expected to fluc- tuate in individual years. In 1931 it was lower than the average, in 1932 still lower. Bul. 564] Bacteriosis of the English Walnut 59 o P w M P p Eh w W QQ ^> 3 5Z5 o 1* Fh n «J CO o CO 1° CO CM d "S o CO CO CD (H 3 03 0> "© CO o 00 od Average increase yield per tree CO © co CO CO Total increase in yield, good nuts §•5 o oo 00 id T3 0> 3 £ a S o r-- S o> CO oo o> ^ o> US CO o © co co cm" cm S CM O t- CM © t>T N « cm" a 1 13 .2 "a a a o> T3 S a aj o -a co 3 "5 | JOS S a « 73 S a al 2 ja a J2 A « 2 to 3> Ph >> OS j-. ft x t3 x 'd - CB 3 01 -0 ■>* £< T3 -* £< ooo fl co o<» s co PQ P> PQ P> CO 0> S ft OO 00 CO CC CT> OS CO co V V S °2 (/}■ >> & O OS >> V 'u 3 C '42 co -S § T3 12 Ph T3 i- C3 o - CM 60 University of California — Experiment Station overloading the trees will result in decreased sizes and even decreased quality of the entire crop on the tree. Therefore an increase in quantity with no decrease in size or quality of the nuts may alone be considered TABLE 13 Additional Cost and Profit Data Secured by E. E. Barrett in an Orchard in Ventura County, California, in 1932 Trees Treatment Total yield Average yield per tree Increase in yield per tree Cost of spray per tree Net gain per Age Num- ber Spray Stage of trees whenapplied tree as Variety Weight Value result of spray Placen- tia 21 years 301 24 Bordeaux 8-4-50 Unsprayed Pre-bloom and post- bloom stage pounds 52,830 3,618 pounds 175.52 150.75 pounds 24.77 dollars 2.48 dollars 1.20 dollars 1.28 TABLE 14 Loss Sustained in 1930 in the Seedling Orchard Belonging to Russell Rowe, Goleta, California, as the Result of Impairment of Nut Sizes Owing to the Control of Bacteriosis Which Caused the Trees to be Overloaded* Nut yields, sizes, and values Cost of spray per tree applied Treatment Grade eizesf Per cent of cropj Pounds Opening price of seedling nuts per pound in 1930§ Value of the nuts at 1930 prices Gross gain per tree as result of spray Net loss per tree as result of spraying f Baby 14% 25% 38% 21% 7% 15% 32% 44% 19.636 34.935 52.516 29.907 7.751 15.179 32.339 43.724 dollars 0.15 \ 0.23 0.15 [ 0.23 dollars 2.95 26.99 1.16 20.99 dollars I 0.65 dollars 1.10 dollars Sprayed^ I Fancy ] Large [ Jumbo ( Baby 0.35 Unsprayed I Fancy | Large [ Jumbo * For complete conditions of the experiment see table 2, p. 40. t Seedling walnuts are graded according to size merely as Large and Baby. They have been graded here as if they were a fancy budded variety merely to show the great fluctuation in sizes of nuts from sprayed and from unsprayed trees. X The average of six crack tests is given. § Large-sized seedling nuts may be packed as Diamond or Emerald according to the quality. In this experiment the Large-sized nuts from both the sprayed and unsprayed trees were Diamond and worth 23 cents per pound that year. The Babies were worth 15 cents. 1 The oil combined with the bordeaux cannot be held responsible for the reduction in nut sizes. A considerable accumulation of data reserved for another paper shows that oil such as was used in this experiment usually tends to stimulate the production of large-sized nuts. an absolute net gain. In table 14 the undesirable effect on nut sizes and values that may result when trees become overloaded as the result of controlling bacteriosis is shown. While the example is extreme it clearly illustrates the truth of the statement just made. Bul. 564] BACTERIOSIS OF THE ENGLISH WALNUT 61 HOW TO SPRAY TO CONTROL BACTERIOSIS Because walnuts are grown in California under widely diversified climatic conditions, any spray schedule proposed for the control of bac- teriosis should be broadly applicable to the state as a whole and at the same time sufficiently flexible to permit of easy adaptation to the pe- culiarities of each individual locality. The problems of the damp coastal regions of northern and central California are considerably different from those met with in the drier portions of the great Sacramento and San Joaquin valleys or in the arid interior counties of southern Cali- fornia. Even the strength of the spray is subject to considerable change. For the state as a whole, bordeaux 8-4-50, which may be regarded as full strength, is recommended. For its preparation see page 71. Experi- mentally the writer has obtained good control at times with spray at half this strength, namely, bordeaux 4-2-50, but several growers have reported unsatisfactory results with it. Since the stronger mixture has consistently given the best results over a period of years the general recommendation is for the stronger spray. There is no point, however, in using the spray at full strength if a weaker and cheaper mixture will meet the requirements of the control consistently and regularly year after year in any given variety or in any particular locality. The grower who has had no especial difficulty in controlling the disease with bor- deaux 8-4-50 might try a few tanks of weaker spray in an experimental way. The weaker spray should be used alongside of the mixture at full strength under similar conditions and the results compared. Whatever the reduction in strength, the same 2 to 1 ratio between the bluestone and the lime should be observed; for instance, 6-3-50 or 4-2-50. No at- tempt to secure results with weaker mixtures should be made in advance of trials with the spray at full strength. It is impossible to state the exact number of applications of spray necessary to guarantee a satisfactory or practical control of the disease in any one year or in any one locality, but at least two must be consid- ered the minimum as a general recommendation. These may be insuffi- cient in very damp regions or in years of greater rainfall in those regions normally dry. Many instances of striking control obtained with only one spray have been observed. Satisfactory control, however, with one appli- cation of spray must be regarded as the exception rather than the rule. There may be years when even two, three, or more sprays may fail to give the practical control sought for, although each additional applica- tion will help. Analogous examples are found in other well-known dis- 62 University of California — Experiment Station Fig. 14. — The pre-bloom stage in the development of the new growth when the first spray must be applied for best results in controlling bacteriosis. (Natural size.) Bul. 564] Bagteriosis of the English Walnut 63 eases such as pear scab, Coryneum blight of peach and apricot, etc., which stubbornly resist control in spite of many applications of spray when climatic conditions are particularly favorable to their develop- ment. The following general recommendations are based upon the personal observations of the writer and experimental data obtained at widely separated localities in California. Winter Sprays. — The disease cannot attack mature or old wood, there- fore it is unnecessary to protect it with winter or dormant sprays. The new growth (including the foliage and nuts) alone is susceptible. Sprays applied in midwinter largely will have lost their strength or disappeared by the time the new growth which needs protection breaks the bud. The First Spray. — The first application of bordeaux 8-4-50 should be given in the spring when the buds are expanding and some of the new growth has developed but when few or none of the nuts have appeared. See figure 14. This is the strategic period for securing the maximum re- sults with any one application of spray. This spray, which has been given the name of "pre-bloom spray," is absolutely indispensable, and it must not be omitted under any conditions in any part of the state or in any year, if spraying is to be done at all for blight. It is a clean-up spray that disinfects the trees, covers over the lesions which have been exuding the living parasites during the rainy winter months, and destroys any great accumulation of the latter on the buds and in more protected parts of the trees. Subsequent sprays are valuable, but each must be regarded merely as an auxiliary or helper to the first one. To delay the application of the first spray beyond the general period described may result in a severe loss, particularly if many of the young nuts have become visible. The young nuts are exceedingly susceptible and may become infected as soon as they appear if climatic conditions are favorable. Incidentally the time it takes the nuts to develop to a point where they are ready for fertilization after their first appearance is very brief indeed. In some varieties the flower lobes actually are al- ready expanded and receptive to pollination when the nuts are first exposed. Spray residue on exposed flowers may easily prevent fertiliza- tion and result in loss of the nuts. Hence the urgent need of a sufficiently early clean-up spray in the trees so that the nuts may be produced under conditions as disease-free as possible and without the risk of interference with their fertilization. See figure 15. If the orchard is large and the spray equipment too limited to permit of spraying all the trees during the critical period mentioned, or if weather forecasts indicate that the weather will be stormy, then it is ad- G4 University of California — Experiment Station BuL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 65 visable to start spraying a little earlier than usual to insure the comple- tion of the job on time. In general to meet emergencies it is better by far to spray just a little too soon than just a little too late. If the orchard consists of seedling trees, which characteristically do not start growth activities in spring as a unit, the first application should be made when a few of the earliest trees have reached the pre-bloom Fig. 16. — Young nuts of the English walnut after they have been pollinized. The dead flower parts are still visible. In some instances the fertilized fruit may be smaller or larger than that shown here. The second spray should be applied just as soon as the flowers have faded regardless of the size of the fruit. (Natural size.) stage. Poor control will result in most years if spraying is delayed until the latest trees have reached this stage ; the crop on the earliest ones may become badly infected while the grower is waiting for all of them to reach the proper stage for spraying. Best results will be obtained if the owners of seedling groves can apply the pre-bloom spray at intervals as the trees reach the proper condition for spraying. This will entail the expenditure of extra time and money, however. The first spray should be applied when the vegetative or fruit buds have reached the critical stage described without consideration of the catkin development during this same period, because the time of catkin production varies greatly with the variety as well as with the season. 66 University of California — Experiment Station The Second Spray. — A second application of spray at full strength should be made as soon as possible after the fertilization period has passed. Figure 15 shows young nuts with flowers in bloom, the critical period in their development, when sprays must be withheld. Not until the bulk of the flowers have faded and turned brown is it advisable to spray the trees again. 22 At this time the nuts will vary in size from a pea to a small olive, according to the variety. See figure 16. The problem presented by the second set of nuts which ordinarily may be expected complicates the situation considerably, but it will be necessary to concen- trate attention on the first set, which usually is the largest. This is par- ticularly true if the weather has been wet. To delay because the second set of nuts is still receptive to pollination may mean an attack of disease that will occasion the loss of more nuts than the second set would ordi- narily produce. The second spray, like the first, is practically indispensable. Whereas the first spray disinfects and cleans up the trees, the second spray is the first to coat the young nuts with a layer of protective poison and give them individual protection. The tendency of most growers is to wait too long before applying the second spray. The Third Spray. — Whether a third spray will be required will de- pend on the locality or the climatic conditions that prevail at the time. If the weather remains damp and there is much fog and rainfall it may be necessary to spray again, particularly if bacteriosis has started to appear and apparently is making headway. It should be remembered that from nine days to several weeks may elapse between the time the initial infection takes place and the time the spot first becomes visible. Consequently there may be many more diseased nuts in a tree than can be seen at any one time. Likewise it should be remembered that neither the spray nor its effects last indefinitely; the residue is constantly being shaken and washed off, and what little remains steadily loses its strength. Also as the nuts expand in size they grow away from the spray residue upon them, exposing new susceptible surface all the time. To hesitate about applying a third spray may mean a loss of much of the beneficial results obtained with the first two. Most orchards are irrigated in late May or early June for the first time. Almost invariably there is a flare-up of bacteriosis after irriga- tions. The application of water to the trees causes the lesions on the nuts 22 In a personal conversation with the writer Mr. Milo N. Wood of the United States Department of Agriculture, who has made intensive studies of walnut pollina- tion, expressed the opinion that as long as any portion of the flower remains green there is still a chance for fertilization of the nut to take place if it has not done so already. Ordinarily the number of nuts fertilized after the flowers have faded per- ceptibly is not great, however. BUL. 564] BaCTERIOSIS OF THE ENGLISH WALNUT G7 and shoots to ooze a black slimy sap that is swarming with the disease- producing bacteria. It collects in drops and spatters down onto healthy nuts below (fig. 8, page 20). Insects also track it about. Probably many of the late infections can be traced to this source. If a third or another spray is considered advisable it should precede rather than follow the irrigation. It will be some little time after irrigation before the ground will be firm enough to bear the weight of a spray rig, and much infection may take place in the interim. By spraying just before irrigation all new as well as old susceptible surfaces will be given a fresh coating of protective material that will enable the nuts to withstand the effects of the irrigation better. For practical purposes, regardless of whether irrigation is practiced or not, the third spray should be applied when the nuts average ] /2 to 1 inch in diameter. It should be kept in mind that there is a greater possi- bility that infection will take place while the season is damp and the nuts still small, than later, when it is dry and the nuts are larger. There is no objection to using as many sprays as may be necessary to control the disease. Whether it will pay to spray two, three, or more times will depend upon the size of the crop, the value of the nuts, etc. If the crop set is small it may not pay to spray more than once. On the other hand the beneficial effects obtained may be lost if adequate protec- tion to the crop is not given later on. The individual grower must solve this problem for himself. See "Cost and Profit of Spraying," page 57. The Cumulative Effect of Sprays. — There seems to be a cumulative control produced by sprays applied to the same trees year after year; already certain growers who have been spraying regularly for four and five years have noted a marked annual decrease in the amount of bac- teriosis in their orchards. It does not stand to reason that such a disease can be wiped out in one year once it has become firmly established, but time may show, as it has already shown in cases of other serious diseases, that persistent and correct spraying may gradually reduce its incidence to a point where costly multiple-spray methods no longer will be neces- sary and the disease will be held in check with a single spray. REASONS WHY SPRAYING MAY FAIL Many growers not wholly familiar with the details of bacteriosis fre- quently associate other walnut troubles, either vague or definite, with it that have no connection whatever. Since the spray schedule devised for the control of bacteriosis cannot possibly prevent or remedy these troubles it may be well to mention them. First, spraying will not bring- about an increase in the natural set of nuts on the tree. It merely pro- 68 University of California — Experiment Station tects those set by nature itself. Spraying will not make light kernels out of "ambers" or prevent the light kernels from turning dark. Darkening of the kernels is occasioned largely by delays in harvesting, unfavorable climatic conditions, etc. Bordeaux can neither make plump kernels out of shriveled ones nor prevent the kernels from becoming shriveled. In- ferior quality of this sort frequently is traceable to insufficient irriga- tion, sunburn, etc. Similarly bordeaux cannot be relied upon to increase the size of the nuts, although some growers believe they have seen evi- dences of its having done so. Spraying will not prevent moldiness of the shells or of the kernels of nuts which have lain on damp ground or which have become moldy in the husks while waiting to be gathered. The use of bordeaux is designed primarily to prevent, not cure, bacteriosis. No spray can cure the disease already established in the nuts, twigs, or leaves. The following discussion is pertinent only to bacteriosis and its con- trol. Careless Spraying Leads to Poor Results. — Unless the entire surface of susceptible tissue is thoroughly coated with spray it is possible for it to become infected. It will pay the grower, therefore, to make every effort to spray his trees as thoroughly as possible. See "The Amount of Spray Needed," page 58, and "The Cost and Profit of Spraying," page 57, for further information on this subject. Too Few Applications of Spray May Lead to Failure. — A typical ex- ample of failure to control bacteriosis satisfactorily as the result of the use of an insufficient number of sprayings may be seen in results ob- tained experimentally in the Campbell Orchard at Goleta (table 3, page 42), where the excellent control afforded by the first spray was lost in one block of trees when no additional sprays were applied. Trees sprayed twice in this orchard yielded an increase in crop that more than paid for both sprays, whereas. those sprayed once did not produce enough extra nuts to pay for the single spray. Delay in Application of the Sprays May Lessen Their Value. — In table 3, page 42, and table 4, page 43, examples of striking control with two sprays are shown. However, in certain instances, even better results could have been had if the second spray had been applied earlier than it was. In one or two cases the second spray was not applied until the disease had reached epidemic proportions. Estimates of the amount of infection in the trees based upon the amount of disease that is visible are untrustworthy. In addition to the nuts actually showing the disease there may be many more that are already infected but which will not develop lesions for some time to come. BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 69 The tendency on the part of growers is to hesitate about making a second or third application of spray largely for financial reasons. Their viewpoint is not difficult to appreciate, but unless bacteriosis is kept under constant vigilance and the trees protected properly with sprays applied at the right time, the money spent will not bring satisfactory returns. Sprays Too Weak in Strength May Fail to Produce Satisfactory Re- sults. — The advisability of using weak spray mixtures is discussed under the heading "How to Spray to Control Bacteriosis," page 61. SPRAY DAMAGE The Interference with Fertilization of the Nuts by Spray Applied During the Pollination Period. — Heavy losses may be occasioned by the interference of spray applied to the open flowers during the pollination period. Heavy losses may also be occasioned by imperfect pollination that has no connection with spraying. Some varieties are notorious for their failure to produce pollen at the time the flowers are open. Others fail only in certain years to release their pollen at the time the flowers are receptive. Growers should not blame losses of this kind on spray that has been applied at the correct time for the control of bacteriosis. Spray Burn and Other Undesirable Effects. — The walnut is peculiarly sensitive to injury by spray materials that ordinarily have no bad ef- fects on most other plants. Bordeaux 8-4—50 was found to be the least injurious of the many materials tried in the course of the experiments. In fact over a period of five years at widely separated points in the state and under the most diversified climatic conditions no spray burn was observed in any of the experiments. The possibility of bordeaux spray burn is acknowledged, however. From time to time growers cooperating with the writer reported burning of the foliage by the spray. Ordinarily the burns occasioned by properly made bordeaux spray are of no great consequence. The damage is quickly outgrown and the crop in no way affected. Improperly made bordeaux may burn the wal- nut severely, or any other plant, for that matter. The new tender foliage is susceptible to burn while it is still reddish in color. As it matures and turns green its resistance increases greatly. Fully developed foliage will tolerate repeated applications of bordeaux at full strength. Spray burn usually manifests itself by a withering and drying out of the leaflets (fig. 17). Frequently the margins alone are killed and distortions result when the living tissue grows away from the dead areas. Killed spots, circular or irregular in outline, may also de- velop on the blades. The killed tissue may fall out after it dries so that 70 University of California — Experiment Station the leaf becomes perforated and ragged in appearance. No actual de- foliation in any appreciable amount occurs. The factors that lead to spray burn of walnut foliage are imperfectly understood. Trees may be susceptible to the injury one year in a certain locality but not the next. This suggests the possible influence of climatic Fig. 17. — Spray burn of English walnut foliage. The shoot on the right is normal. The shoot on the left shows the characteristic perforation and desic- cation of the leaflets. (Two-thirds natural size.) factors. Most burning seems to take place when the sprays are applied during hot windy weather when the humidity is low, but exceptions to this observation have been noted. It might be advisable to avoid spray- ing on warm days when the humidity is low, such as prevail at times in southern California. Mr. Floyd Stone, in charge of one of the Bowman-Kuhn orchards at San Jose, has sprayed with bordeaux 8-4-50 for a number of years (see table 2, page 40, and table 3, page 42) with and without spray burn. His crop yields have been excellent. At the writer's request Mr. Stone tried different bordeaux formulas on large blocks of trees in an effort to find a mixture that would not burn the foliage under the conditions pe- culiar to the orchard. The results were unsatisfactory. When equal amounts of Milestone and lime were used, the spray burn was just as severe as when bordeaux 8-4—50 was used. Similarly, bordeaux used at half the usual strength, namely 4-2-50, occasioned as much burn as the mixture used at full strength. The method of mixing the spray seems to Bul. 564] BACTERIOSIS OF THE ENGLISH WALNUT 71 have little bearing on the matter; the addition of either the lime or the bluestone to the tank first will not render the spray less likely to burn the foliage when climatic conditions are conducive to it. Some growers have reported that bordeaux spray to which about 1 per cent of highly refined emulsified oil (100 per cent unsulfonated residue) has been added is less likely to burn the foliage than the straight mixture. Mr. Stone tried less highly refined oil emulsions at the same strength with the same object in view. 23 These oils were used because they are considerably cheaper. There seemed to be less burning where the combination was used, although it was not entirely prevented. The Franquette, Mayette, and Eureka varieties seem more suscep- tible to spray burn than either the Payne or the Santa Barbara Soft Shell. Mechanical Injuries Occasioned by the Spray. — Spray applied under pressure is likely to bruise and tear the foliage, particularly on the lower branches. Bruised and lacerated tissue may die and leave spots or per- forations. Injured tissue may be damaged further by spray burn. Me- chanical injuries of this kind are quickly outgrown and may be ignored. The proper manipulation of the spray gun when spraying the lower limbs will obviate much of this kind of damage. THE PREPARATION OP BORDEAUX SPRAY The ingredients which make up bordeaux spray are bluestone (copper sulfate), quicklime (calcium oxide), and water. To designate the proportions of bluestone and quicklime used it is customary to write the formula immediately after the name of the spray, such as bordeaux 8-4-50. In such a formula the first figure always indi- cates the number of pounds of bluestone used, the second figure the number of pounds of quicklime, and the third figure the number of gal- lons of water. The grower who intends to spray regularly, particularly if the or- chard is a reasonably large one, should familiarize himself with the great advantages of an elevated platform from which concentrates or stock solutions can be run directly to the spray tank with less trouble, delay, and muss than when the spray must be mixed from barrels on the ground. An overhead water supply of good volume is practically indis- pensable. Also, for cleanliness and convenience, a level concrete base and 23 The oil emulsions used were Ortliol-K-Medium and Medium Summer Oil, manu- factured by the California Spray Chemical Company, Berkeley, California, and the San Jose Spray Manufacturing Company, San Jose, California, respectively. Ordi- narily neither emulsion is toxic in itself to walnut foliage. 72 University of California — Experiment Station drain for the spray rig to stand upon when the spray is being made, or when the tank is being washed out, is much to be recommended. The following method is designed for the grower who has few or none of the conveniences described above, but in general the principles in- volved are the same as used in any method of making bordeaux. Preliminary Preparations. — First, secure at least 4 water-tight, clean wooden barrels of 50-gallon capacity. To work with less than 4 barrels will delay the work of spraying, and since the nature of the disease is such that everything must be done to facilitate the job of spraying, it is poor economy to work with too few barrels. If the orchard is large and much spray is to be used, 6, 8, or even more barrels, will be found to be none too many once the work is under way. See that the barrels are thor- oughly clean and well soaked up. Provide a coarse bristle brush and an extra barrel of water for the purpose of washing buckets, etc. Place the barrels on level ground in a position convenient to the water supply. With a bucket or other liquid measure, the capacity of which is definitely known, very accurately pour 40 gallons of water into each barrel. Drive in two brass or copper nails opposite each other on the inside of each barrel at the 40-gallon level. Do not remove the nails, be- cause the barrels will be used again and again. Empty the barrels. Preparation of Stock Solution of Bluestone. — In each of two or more barrels, in which the 40-gallon level has previously been determined, dis- solve 80 pounds of bluestone. The bluestone should be of good grade, which may be recognized by its deep blue or sapphire color. A green color indicates the presence of iron impurities, and such bluestone should be rejected. Place the bluestone in a clean, fairly loosely woven gunny sack free of holes. Avoid the use of heavy interwoven sacks which do not permit of free circulation of water within. Tie the sack closely to a wooden bar of some sort such as an old axe, pick, or broom-handle and suspend the bluestone in the middle of the empty barrel in such a way that it touches neither sides nor bottom. Pour boiling hot water into the barrel to dissolve the bluestone. Boiling water is easily obtained as follows when no more convenient source is at hand : Dig a fairly deep trench close to the water supply and away from the wind. Place four iron bars or pieces of pipe across it to support two ordinary 10-gallon wash tubs full of clean water. The tubs should be provided with flat tin lids. Build a good fire in the trench, which for the sake of convenience should be dug not wider than the tubs. The contents of the two tubs (roughly 20 gallons) will quickly come to a boil and will be sufficient to dissolve the bluestone in one barrel in a few minutes. Cold water may be added either before or after all of the blue- stone has dissolved to bring the water level up to the 40-gallon mark. If BUL. 564] BACTERIOSIS OF THE ENGLISH WALNUT 73 hike-warm water is used it may take several hours to dissolve the blue- stone. If cold water is used it may take several days, according to the chill of the water. To speed up the solution of the bluestone, the sack may be shaken from time to time. When the last bluestone crystals have disappeared remove the sack from the barrel. Carefully note whether the solution has reached the 40-gallon mark. If not, add the necessary amount of cold water to bring up the level. Stir the solution with a wooden paddle until it is evenly mixed throughout. Once thoroughly mixed it needs no further stirring at any time, and the paddle may be removed. The barrel now contains 40 gallons of bluestone stock solution (not 40 gallons of water) in which 80 pounds of bluestone have been dissolved. Each gallon of solution, therefore, contains 2 pounds of bluestone. The stock solution is ready for use. Under no circumstances prepare bluestone stock solution in an iron barrel or other vessel in which iron is exposed because the bluestone will destroy it. Even iron nails used to mark levels in barrels will disappear, necessitating recalibration of the 40-gallon level. Preparation of Stock Solution of Lime. — Since only one-half as much quicklime is used as bluestone in the bordeaux 8-4-50 formula, smaller quantities of lime stock solution may be made. In one or more clean, empty wooden or iron barrels, the 40-gallon level of which has previously been determined, dump 80 pounds of good- quality, freshly burned quicklime (unslaked lime). Add cold water until the quicklime is almost covered, and allow the mixture to come to a boil of its own accord. Sluggish lime which will not raise the tempera- ture of the water to the boiling point should be returned to the dealer who supplied it. Quicklime rapidly deteriorates on exposure to the air and becomes "air-slaked." As the quicklime air-slakes it sloughs away from the lump form in which it usually comes, into a very fine, flour- like, white dust. The presence of much of this white dust in the barrel should cause it to be looked upon with suspicion. Air-slaked lime is utterly worthless in the preparation of bordeaux, and serious burns may result if it is used. Many companies manufacturing quicklime realize the difficulty of keeping it fresh in wooden barrels and now pack their product in air-tight tin drums. Such quicklime if originally obtained from a good quarry is apt to be the best. Some companies using metal drums pulverize the quicklime to conserve space. Such pulverized or powdered quicklime is as good as any provided it is fresh. In such cases the readiness and thoroughness with which it reacts with water will be the sole proof of its freshness. 74 University op California — Experiment Station Some pulverized quicklimes of high purity, packed in metal drums, are so violent in their reaction with water that it is often desirable to start with the barrel about two-thirds full of cold water instead of empty as described above. The requisite amount of quicklime should be poured into the water at a rapid rate. Ordinarily the entire amount can be in- troduced into the barrel before the temperature of the water is raised to the boiling point. If the mixture becomes violent before all the quick- lime has been introduced, the worker should wait a moment until the reaction subsides. Or the temperature can be lowered by the addition of more cold water to the barrel, after which the remainder of the quick- lime may be added conveniently. The quicklime should be stirred occasionally while it is being slaked to insure that water reaches all of it. Add water from time to time to prevent the mass from drying out and finally enough to bring the level up to the 40-gallon mark. After the reaction is complete and boiling has ceased, the mixture should be stirred vigorously for a few minutes until all lumpy material or paste in the bottom of the barrel has disappeared and a smooth "milk of lime" obtained. Small quantities of impurities such as grit, rock, or unburned lime may be ignored. The barrel now contains 40 gallons of lime stock solution (not 40 gal- lons of water) in which 80 pounds of quicklime have been slaked. Each gallon therefore contains 2 pounds of quicklime. The lime stock solution is ready for use. Preparation of the Spray from the Stock Solutions. — The stock solu- tions of bluestone and lime should be made at a convenient time before they are apt to be needed. Each one separately keeps practically in- definitely but when one is added to the other the resultant mixture must be used at once, as it deteriorates rapidly on standing, losing both its adhesive properties and its value as a disinfectant. The spray should always be prepared with cold water. There is no objection to using the stock solutions while they are still hot, however, if the following method of mixing the spray is observed. First determine the amount of bluestone and lime stock solution that must be used to make a tank of bordeaux 8-4—50. The formula itself provides for 50 gallons of spray only. Multiply the numbers of the for- mula by the number of times that 50 gallons will go into the spray tank. The calculations for 200, 300, and 400-gallon tanks would be as follows : 8-4-50 8-4-50 8-4-50 X 4 X 6 X 8 82-16-200 48-24-300 64-32-400 Thus for a 200-gallon tank, it will be necessary to use 32 pounds of bluestone and 16 pounds of quicklime as shown above. Since each gallon BUL. 5C4] BaCTERIOSIS OF THE ENGLISH WALNUT 75 of the stock solutions contains 2 pounds of either Milestone or quicklime, it will be necessary to take 16 gallons of Milestone stock solution and 8 gallons of the lime stock solution to give the requisite amounts. The amount of stock solution to use in tanks of other sizes is deter- mined in exactly the same way; thus for a 400-gallon tank, take 32 gal- lons of the bluestone stock solution and 16 gallons of the lime stock solu- tion to give the requisite amounts of Milestone and quicklime. Dip the bluestone solution with a wooden bucket; it destroys iron pails quickly. Always wash the pails after finishing with one solution before using them in the other. To mix the spray proceed as follows : First fill the tank y 2 to % full of clean, cold water. Next add the bluestone stock solution through a sieve of about 20 meshes to the inch, to exclude grit and other foreign sub- stances which otherwise may reach the valves or nozzles and give trouble. Start the agitator running, and add the requisite amount of lime stock solution last. Always stir the lime stock solution vigorously before drawing, because the lime tends to settle out on standing. If the solution is thoroughly stirred each time before using it will be no more concentrated at the bottom of the barrel than at the top. When the lime stock solution is thoroughly mixed it should run freely through the sieve into the tank. Lime stock solution that is pasty may be hosed through the sieve easily. Carefully remove the sieve and shake out the grit, dirt, and other debris. Fill any space that may remain in the tank with water and proceed to spray at once. Never stop the agitator at any time after starting to mix the spray until the last of it has been applied to the trees. Opinions are divided as to whether the bluestone or the quicklime should be added to the tank first, There seems to be little difference in the bordeaux produced by the two methods or in the effects produced on the walnut tree. The writer has always added the bluestone to the tank first and the lime last with excellent results. Stock solutions left over may be saved for use later on. Drive a copper nail at the level of the solution when finished with it. Just before using the solution add water to bring the level up to the nail, to replace the water that has been lost by evaporation. Stir the mixture vigorously, and the original 2-pounds-to-a-gallon ratio will be restored. The Use of Commercial Bordeaux. — The use of bordeaux powders in which the Milestone and quicklime have been combined chemically is not advised. The adhesive properties of such powders are very poor and their value as disinfectants distinctly inferior to those of freshly pre- pared bordeaux. 76 University of California — Experiment Station So-called "two package," "twin," or "instant" bordeaux more closely approximates the freshly prepared spray than does the powdered form. In such preparations the bluestone is contained in one bag, lime in an- other. The bluestone is powdered fine enough to dissolve readily in cold water when added to the tank, thus obviating the use of hot water as described earlier in this section. The lime is already slaked (hydrated) and need not be prepared in advance as when quicklime is used. Some bordeaux chemists not averse to commercial bordeaux of this type recommend soaking the hydrated lime overnight in water, however, be- fore making the spray, for best results. This, of course, necessitates the use of barrels as when bordeaux is made from quicklime. The greatest recommendation of commercial preparations of this type is the ease with which bordeaux spray can be prepared from them. They possess certain objectionable features, however, which may lead to serious trouble at times. Dry hydrated lime when exposed to air is read- ily converted into a carbonate and as such is utterly useless in the prep- aration of bordeaux. The paper bags in which the hydrated lime is sold are not wholly impervious to air. Likewise they are easily punctured; this permits air-slaking to take place, though the change is not evident in the appearance of the material. The more reputable manufacturers recognize this danger and replace it in the market with fresh material after a reasonable length of time. Severe burns may result when old lime is used. There can be no objection to the use of pulverized bluestone in the preparation of bordeaux spray provided the price is satisfactory and the material ground fine enough to permit of complete and immediate solution in cold water when it is added to the tank. The writer has used some commercial products, however, which did not dissolve readily but collected in the corners and bottom of the spray tank. This may happen even with the best material if sufficient agitator blades are not used or if some of them are not properly adjusted. Undissolved bluestone sprayed on the foliage will cause burns. Freshly prepared bordeaux spray was used exclusively in all the experiments reported in this paper, but cer- tain excellent results have been obtained by walnut growers with the two-package type. From the standpoint of cheapness and efficacy, home- made bordeaux, the preparation of which is described on page 71, can- not be excelled. BUL. 564] BaCTERIOSIS OF THE ENGLISH WALNUT 77 LIST OF MATERIALS TRIED WITH DOUBTFUL, LIMITED, OR UNFAVORABLE RESULTS For the sake of record a report is given here of the various spray ma- terials tried with limited, doubtful, or unfavorable results. Some of the materials seemingly produced good results on their first trial but failed to repeat them in subsequent experiments. Others burned the foliage or poisoned the trees. As a whole they may be regarded as failures. Indi- vidual materials need be discussed in detail sufficient only to show why they were unsuited. 24 Highly Refined Oil Emulsions (Unsulfonated Residue 100 per cent). — Several types were used at 2 and 5 per cent strengths in single and multiple applications as described on page 33. They afforded no pro- tection whatever. Basic Copper Acetate. — This material was used at the rate of 4 pounds in 50 gallons of water, either with or without ground glue (pre- viously dissolved in hot water) at the rate of 1 pound to 50 gallons of spray as an adhesive. Single and multiple applications were given as described on page 33 for a period of three years. Basic copper acetate afforded an appreciable amount of control at times, but bordeaux 8-4-50 used alongside of it under identical conditions consistently gave better results. At times there was a distinct tendency on the part of the copper acetate spray to russet the foliage and nuts. This was avoided by reduc- ing the strength from 4 pounds to 3 pounds in 50 gallons of water. Ammoniacal Copper Carbonate. — The standard formula was used : Copper carbonate 5 ounces Ammonia (26° Baume) 3 pints Water 50 gallons Used in moving plots over a period of several years, this spray, like basic copper acetate, afforded an appreciable amount of control, but was inferior to bordeaux 8-4-50. Unlike basic copper acetate it did not burn or russet the foliage. Borco, a proprietary product said to produce ammoniacal copper car- bonate when dissolved, was used at the rate of 12 pounds in 200 gallons of water. Borco Spred at the rate of 1 pound in 200 gallons of the spray was added according to the directions of the manufacturers. 25 Used in 24 Many of the chemical and proprietary spray materials reported here as failures in the control of walnut bacteriosis have been found highly effective in the control of other plant diseases. It was their success in other fields that led to their use in the present experiments. The fact that they failed to control bacteriosis should not preju- dice growers against their use in fighting diseases for which they may be better suited. 25 "Borco" and "Borco Spred" are manufactured by the Eex Eesearch Company Inc., of Toledo, Ohio. 78 University of California — Experiment Station moving plots as described on page 33 the results were identical with those obtained with freshly prepared ammoniacal copper carbonate. Acid Bordeaux. — A solution of bluestone (8 pounds to 50 gallons of water) was treated with such small amounts of quicklime (previously slaked in water) that the resultant bordeaux was definitely acid to lit- mus. After 10 minutes' agitation some of the spray was filtered and the filtrate tested with a solution of potassium f errocyanide for the presence of soluble copper. A bright rose or pink color was produced, showing copper to be present in the filtrate. Acid bordeaux was applied in moving plots as described on page 33. Its action was undependable; rather severe burns were occasioned one year and not the next. The worst damage occurred on the trees to which the spray had been applied several times. While acid bordeaux showed distinct disinfectant properties (see table 2, page 40), the control afforded by it was no greater than that of the alkaline mixture. Its greater tendency to burn the foliage and the difficulty of preparing it make its use inadvisable. Neutral Bordeaux. — Prepared exactly like acid bordeaux but with the addition of more quicklime to make the spray neutral to red or blue litmus. The filtrate when tested with potassium ferrocyanide failed to show the presence of copper ions. The results obtained with neutral bordeaux were practically indistin- guishable from those of acid bordeaux. Undependable in its action on the foliage, it sometimes occasioned pronounced burns, at other times no appreciable damage. Its use by growers is not considered advisable. Excessively Alkaline Bordeaux. — Various bordeaux formulas were tried in which the quicklime content varied in weight from an amount equal to that of the bluestone used to twice as much. None of these sprays afforded any greater control than bordeaux 8-4-50. Sprays of this type are harder to apply and leave a very dense, opaque residue resembling whitewash, which is highly undesirable on the shoots and foliage. When bordeaux 6-12-50 was used, the very great excess of lime present was injurious to the valves and pressure regulator of the spray pump. The seating pin in the latter had to be replaced from time to time as the result of the abrasive action of the spray. Semesan. — Semesan (hydroxymercurichlorophenol sulfate 30 per cent, inert material 70 per cent) formerly was manufactured by E. I. Du Pont de Nemours and Company of Wilmington, Delaware, and was used in moving plots on Payne walnut trees at the rate of 0.25 per cent for the first two applications. In blocks of trees receiving the third and fourth applications in summer, the strength was cut to 0.12 per cent, because it was observed that with the approach of warm weather the Bul. 564 j BACTERIOSIS OF THE ENGLISH WALNUT 79 foliage sprayed with the stronger concentration turned yellowish and at times showed a faintly speckled condition reminiscent of, but not always identical with, true spray burn. Even at weaker concentrations the material applied in midsummer induced this same condition in trees sprayed for the first time. In another moving plot, the experiment was duplicated in every detail except that Volck oil, 2.0 per cent in strength, was used in combination with the Semesan. In all blocks of trees sprayed with Semesan alone or in combination with oil, there was no appreciable control of the disease regardless of the number of applications given. The trees appeared to be normal at the close of the season, but during the following winter they died back badly, in many instances almost to the main trunk, regardless of the strength at which the material had been used or whether it had been combined with oil or used in single or multiple applications. The severest damage was observed in the blocks receiving multiple applications of the spray. Symptoms of poisoning were very apparent the following spring; the new foliage appeared much later than that on adjoining un sprayed trees and was yellowish in color. Growth was sluggish throughout the season. Melilotus seed planted for a covercrop during the winter failed to germinate under the trees sprayed with Semesan. Outside of the sprayed plots, however, there was a luxuriant growth waist high. Uspulin. — Uspulin (hydroxymercurichlorophenol sulfate 30 per cent, inert material 70 per cent) formerly manufactured by the Bayer Com- pany of Rensselaer, New York, has been withdrawn from the market. It was used at the rate of 0.25 per cent with and without 2.0 per cent Volck oil in moving plots on Payne walnut trees, from one to four times. As in the case of Semesan the strength of the Uspulin had to be reduced to 0.12 per cent with the approach of warm weather. Uspulin alone or in combination with oil produced highly undesirable effects, identical with those produced by Semesan, regardless of its strength or whether it was used in single or multiple applications. A comparison of the weights of nuts from sprayed and unsprayed plots adjoining revealed no appre- ciable control of the disease. The quality of the nuts from sprayed trees was distinctly inferior to those from unsprayed trees. During the winter following the experiment the sprayed trees died back badly. Melilotus seed planted for a covercrop failed to germinate under the sprayed trees. Dip Dust. — Dip Dust (hydroxymercurichlorophenol sulfate 6 per cent, hydroxymercurinitrophenol sulfate 2 per cent, inert ingredients 92 per cent) formerly manufactured by the Bayer Company of Rensselaer, New York, has been withdrawn from the market. Used at 0.25 per cent 80 University of California — Experiment Station strength it gave considerable promise, but final conclusions could not be drawn under the conditions of the experiments. Large blocks of trees sprayed one and two times with it early in the growing season of 1928 were seemingly unaffected in any way. The crop was lost to frost, how- ever, and the value of Dip Dust as a disinfectant could not be deter- mined. The following year with limited material available, 11 trees were sprayed a single time with it when the nuts were about the size of peas. No ill effects were noted throughout the balance of the season. In a part of the orchard where the natural set of fruit varied considerably, the trees sprayed with Dip Dust produced a huge crop, averaging 216 pounds hulled nuts per tree, wet weight, against 171 pounds average on 11 check trees seven rows away. Dip Dust was very expensive, and it is doubtful whether it would pay to use it regularly. Dip Dust was almost entirely colloidal and practically insoluble in water in contradistinction to Semesan and IJspulin, which were almost entirely soluble. Nelw. — Neko is a germicidal soap containing 2.0 per cent mercuric io- dide manufactured by Parke, Davis, and Company of Detroit, Michigan. It was used at strengths varying from 0.25 per cent to 0.10 per cent on Payne walnuts. Even at the weaker concentration it caused severe burn- ing of the leaves, retarded the growth of the new shoots, and stunted the nuts in size. Pending further experiments its value as a disinfectant must remain undecided. Iodine. — A saturated alcoholic solution of iodine was prepared by placing an excess of iodine crystals in methyl alcohol. The solution was used at 0.50 per cent strength in water in which 2.0 per cent fresh quick- lime previously had been slaked. Also it was applied as weak as 0.06 per cent in water containing 1.0 per cent cooked cornstarch, added as an ad- hesive. At any strength at which it was used the iodine caused severe burning of the foliage of Payne walnuts, delayed the new growth, and stunted the nuts in size. No trees were sprayed more than once with iodine in any dilution because of the severe reactions which it caused. After two years' trial this element was considered unsuited for use as a disinfectant on walnuts. Liquor Cresolis Compound, Surgical. — A liquid soap containing 50 per cent Cresol, IT. S. P., manufactured by the Michel and Pelton Com- pany of Oakland, California, used at 0.5 per cent strength in water, in which 1.0 per cent fresh quicklime had previously been slaked. Payne walnut trees were sprayed with the mixture when the new growth was starting in the spring and again when the nuts were the size of peas. No ill effects were noted. The crop was destroyed by frost, consequently the value of the spray could not be determined. Used the following year only once at 0.35 per cent strength without any lime on 11 trees when Bul. 564] BACTERIOSIS OF THE ENGLISH WALNUT 81 the nuts were the size of peas, the mixture occasioned no injury. The disease developed as early on the sprayed trees as on check trees close by, and a comparison of the weight of nuts from the two plots at har- vest showed no evidence of control. The possibilities of this material were not exhausted, but in view of the volatile nature of its active prin- ciple it is not likely that bacteriosis can be effectively controlled with it. Sodium Fluosilicate. — Sodium fluosilicate was applied at the rate of 8 ounces in 400 gallons of water to Payne walnut trees from one to four times in moving plots. In a similar moving plot the material was applied from one to four times at the same strength in combination with 2 per cent Volck oil. The cumulative effect of the sodium fluosilicate was very bad, either when used alone or in combination with oil. Even at the very weak concentration at which it was used it burned the foliage severely. No control of the disease was effected, there being just as many good nuts harvested in the check plots on all sides as in any of the sprayed blocks. Calcium Chloride. — Calcium chloride was used at the rate of 1.0 per cent concentration in water from one to four times on Payne walnut trees in moving plots. In a similar moving plot this material was used again at the same strength in combination with 2.0 per cent Volck oil. Used alone or in combination with oil the calcium chloride produced undesirable effects on the trees. Less apparent in plots sprayed once, spray burn was very noticeable in plots sprayed several times. The ma- terial effected no appreciable control of the disease; the crop was just as large by weight in check plots on all sides as in the plots sprayed with calcium chloride alone or in combination with oil. Potassium Permanganate. — Potassium permanganate was used at 1.0 per cent concentration in water in limited experiments from which no final conclusions as to its worth as a disinfectant could be drawn. The material occasioned no damage to the trees. Because of the rapidity with which potassium permanganate loses its disinfectant properties it is not likely to prove satisfactory as a spray in the control of walnut bacte- riosis. Zinc Sulfate and Quicklime. — The method of preparing the spray is similar to that of bordeaux. The formula used was 4-4-50. The zinc sul- fate was added to a spray tank about two-thirds full of water. The agi- tator was started and the lime (previously slaked separately) poured in. The tank was then completely filled with water. This mixture was tried only once on Payne walnuts during the pre- bloom stage. There were no appreciable results. The experiment was never repeated and no final conclusions were drawn. 82 University of California — Experiment Station ACKNOWLEDGMENTS Much of the data presented throughout this paper has been compiled by the growers themselves working under my direction. Grateful ac- knowledgment is made to them all collectively at this point. Many of their names appear in the text and in the tables. Acknowledgments should be made particularly to the Anderson-Barngrover Ranch Com- pany, the Anderson Orchard Company, the W. C. Anderson family, and to Mr. Raymond Miller, all of Linden. These growers placed their large orchards entirely at my disposal at the opening of the work, in the face of almost certain damage to their trees by chemicals or spray materials, either new or hitherto untried on walnuts. Some of these materials occa- sioned very severe burns, especially in the Anderson-Barngrover Ranch Company orchard, but every inducement to continue the work was made. Acknowledgment is also made to Dr. E. 0. Campbell, Mr. Russell Rowe, the Bishop Ranch (Mr. W. Main, in charge) and to Mr. W. Hamilton, all of Goleta; to Mr. R. E. Barrett, of Saticoy ; and to the Hurst Brothers, of West Covina; upon whose orchards many of my experiments were conducted, and to Mr. W. Hollister of Goleta for his considerable assist- ance with the experiments in that vicinity. Lastly I wish to acknowledge the help of Mr. W. B. Hooper, formerly Walnut Extension Specialist of the University of California, who assisted both with the spraying experiments and in determining the results over a wide area in southern California. Bul. 564] BaCTERIOSIS OF THE ENGLISH WALNUT 83 BIBLIOGRAPHY 26 i Ames, S. 1928. Spraying for walnut blight. Oregon State Hort. Soc. 19th Ann. Eept. p. 181-184. 2 Ames, S. 1929. Spraying for walnut blight. Washington State Hort. Soc. Proc. 24th Ann. Meet. p. 202. s Anonymous. 1899. Bacteriosis of the walnut. Pacific Rural Press 57(25) :387. 4 Anonymous. 1908. Annual report of diseases and injuries on cultivated and useful wild plants. Russia Dept. Agr. Bur. Mycol. and Phytopath. of the Scientific Committee. (St. Petersburg.) 3rd Rept. (1907). p. 196. 5 Anonymous. 1923. Walnut-blight. The introduction of immune variety by the department. New Zealand Jour. Agr. 27(1) : 25. 6 Anonymous. 1926. Black spot on walnuts. Garden and Field (Australia) 51(1) :13. 7 Barss, H. P. 1913. Diseases of nut crops. Oregon Agr. Exp. Sta. Bien. Crop Pest and Hort. Rept. 1911-12; 1:260-261. 1 fig. s Barss, H. P. 1927. Bacterial blight of walnuts. Oregon State Hort. Soc. 18th Ann. Rept. p. 196-199. 9 Barss, H. P. j 930. Some preliminary experiments on the control of bacterial blight of wal- nuts conducted in Oregon in 1929. Oregon State Hort. Soc. 21st Ann Rept. p. 120-127. io Batchelor, L. D. 1924. Walnut culture in California. California Agr. Exp. Sta. Bul. 379:1-91. 34 fig. Revised by L. D. Batchelor and O. Lee Braucher, 1929. i i Bergey, D. H. 1930. Manual of determinative bacteriology, 3rd ed. p. 240. Williams and Wil- kins, Baltimore. 12 Boucher, W. A. 1900. Bacteriosis of the walnut. New Zealand Dept. Agr. 8th Ann. Rept. p. 334-335. 13 Camacho, C. 1917. Enfermedades del nogal. Bacteriosis o peste negra del nogal [Bacteriosis or the black plague of the walnut]. 13 p. 3 fig. Servicios de Policia Sanita- ria Vejetal. Estacion de Patolojia Vejetal, Santiago, Chile. 14 Capdeville, C. Cesar. 1926. Las enfermedades del nogal [Walnut diseases]. Bol. Soc. Nac. Agr. [Santiago, Chile] 57(9) :595-597. 20 All references are concerned with bacteriosis of the walnut. No attempt to re- view the literature later than 1932, when this paper was written has been made. Occasional later references have been included when convenient. 84 University of California — Experiment Station is Cole, C. F. 1914. The walnut. Jour. Dept. Agr. Victoria I Australia] 12(8) :445-461. 5 fig. i« Cole, C. F. 1916. The walnut. Jour. Dept. Agr. Victoria [Australia] 14(3) : 154-161. 3 fig. 17 Cook, M. T. 1921. Keport of the department of plant pathology. New Jersey Agr. Exp. Sta. 33rd Ann. Kept. p. 570. isDoidge, E. M. 1918. Walnut bacteriosis, Bacterium juglandis Pierce. So. African Jour. Sci. 15 (6) :407-412. 19 Doidge, E. M. 1918. Walnut blight. So. African Fruit Grower 5:68-69. 2 fig. 20 Doidge, E. M. 1919. The role of bacteria in plant disease. So. African Jour. Sci. 16(2) :69, 73, 84. 2i Elliott, C 1930. Manual of bacterial plant pathogens. 349 p. Williams and Wilkins, Bal- timore. 22 Evans, I. B. P. 1922. Botany and plant pathology. Union So. Africa Dept. Agr. Jour. 4:55-59. 23 Fawcett, H. S., and L. D. Batchelor. 1920. An attempt to control walnut blight. California Dept. Agr. Mo. Bui. 9 (5-6):172-174. 1 fig. 24 Ferraris, T. 1926. Trattato di patologia e terapia vegetale [Treatise on plant pathology and therapy]. 3rd ed. p. 121. V. Hoepli, Milan, Italy. - 5 Galloway, B. T. 1894. Walnut disease. Eeport of the Chief of the Division of Vegetable Path- ology. Report of the Secretary of Agriculture. U. S. Dept. Agr. Rept. 1893:272. 26 Gussow, H. T. 1911. Bacterial blight of English walnut (Juglans regia L., Bacterium [Pseudo- monas] juglandis Pierce). Canada Dept. Agr. Exp. Farms Rept. 1910-11: 252. -~ Jardine, J. T. 1930. Oregon Agr. Exp. Sta. Director's biennial report 1928-30:81. 28 Kirk, T. W. 1907. Plant diseases due to bacteria. Walnut blight {Pseudomonas juglandis) . New Zealand Dept. Agr. 15th Ann. Rept. p. 167-168. 29 Kirk, T. W., and A. H. Cockayne. 1909. Bacterial diseases of plants. New Zealand Dept. Agr. Div. Biol. Bui. 23 : 1-8. 1 pi. so Lake, E. R. 1913. The Persian walnut industry of the United States. U. S. Dept. Agr. Bur. Plant Indus. Bui. 254:1-112. 10 pi. 24 fig. si Lewis, C I. 1906. The walnut in Oregon. Oregon Agr. Exp. Sta. Bui. 92:1-43. 23 pi. 32 McMurran, S. M. 1917. Walnut blight in the eastern United States. U. S. Dept. Agr. Bur. Plant Indus. Bui. 611:1-7. 2 pi. Bul. 564] Bacteriosis of the English Walnut 85 sa Miller, P. W. 1931. A report of progress on studies of the life history and control of walnut blight in Oregon. Oregon State Hort. Soc. 22nd Ann. Eept. p. 142-156. 34 Miller, R. W. 1926. To start new walnut blight investigation. California Cultivator 67(12) : 293, 301. 35 Muller-Thurgau, H., and A. Osterw alder. 1924. Bericht der Schweizerischen Versuchsanstalt fur Obst-, Wein-und Garten- bau in Wadenswil fur die Jahre 1921-1923. III. 1. Pfianzenphysiologische and Pflanzenpathologische Abteilung [Report of the Swiss experiment station for pomology, viticulture and garden culture, at Wadenswil for the year 1921-1923. III. 1. Section on plant physiology and plant path- ology.] Landw. Jahrb. Schweiz 38(5) :573-574. 36 Osborn, T. G. B., and G. Samuel. 1922. Some new records of fungi for South Australia. Part II. Roy. Soc. So. Australia. Trans. 46:166-180. 1 pi. 4 fig. 37 Pierce, N. B. 1896. Bacteriosis of walnuts. California Fruit Grower 19(13) :243. ss Pierce, N. B. 1896. A word more on bacteriosis of walnuts. California Fruit Grower 19(16) : 316. so Pierce, N. B. 1896. Bacteriosis of the walnut. Rural Californian 19(10) :407. 40 Pierce, N. B. 1898. The walnut disease. Pacific Rural Press 55(26) :404. 4i Pierce, N. B. 1899. Bacteriosis of the walnut. Pacific Rural Press 57(25) : 387. *2 Pierce, N. B. 1901. Walnut bacteriosis. Bot. Gaz. 31(4) :272-273. 43 Pierce, N. B. 1909. Walnut bacteriosis. In: Bailey, L. H. Cyclopedia Amer. Hort. 4:1961- 1962. 1 fig. 44 Ramsay, H. J. 1908. The possibility of walnut blight control by use of immune varieties. Pa- cific Rural Press 75(14) :212-213; (15) :228-229. 45 RODWAY, L. 1912. Bacterial black spot of walnut. Tasmania Agr. Gaz. 20(3) :85-86. 46 Rudolph, B. A. 1930. On spraying for blight control. Diamond Walnut News 12(1) :10-11. 47 Rudolph, B. A. 1931. Four years of research in walnut blight control. Diamond Walnut News 13(1) :8-9. 48 S AVAST ANO, L. 1923. Delle epidemie italiane del mal secco negli agrumeti, albicoccheti, ficheti, noceti e gelseti [On the Italian epidemic of the dry disease in citrus groves, apricot orchards, fig orchards, walnut groves, and mulberry groves]. Ann. R. Staz. Sper. Agrumic. e Fruttic. Acireale 7:146-150. 48 Schattenberg, G. A. •■-"■ • 1908: The future of the walnut industry in southwest Texas. Texas Dept. Agr, Bul. 2:42-43. 86 University of California — Experiment Station so Schuster, C. E. 1928. English walnut production in Oregon. Oregon Agr. Exp. Sta. Cir. 91:1-48. 24 figs. 5i Smith, C. O. 1914. Walnut blight or bacteriosis. Amer. Nut Jour. 1:32-33, 67. 3 fig. 52 Smith, C. O. 1915. Walnut blight experimental work. Amer. Nut Jour. 2:46. ss Smith, C. O. 1915. Walnut blight or bacteriosis. California Dept. Agr. Mo. Bui. 4(5 and 6) : 254-258. 1 fig. 54 Smith, C. O. 1921. Some studies relating to infection and resistance to walnut blight. Cali- fornia Dept. Agr. Mo. Bui. 10(9) :367-371. 1 fig. 55 Smith, C. O. 1922. Some studies relating to infection and resistance to walnut blight, Psuedo- monas juglandis. Phytopath. 12(2): 106. se Smith, C. O. 1924. Eecent investigations of walnut blight. Amer. Nut Jour. 20(2) :22. 1 fig. 57 Smith, E. F. 1905. Bacteria in relation to plant diseases. Carnegie Inst. Wash. p. 171. pi. 21 and 22. ss Smith, E. F. 1920. Bacterial diseases of plants, p. 55, 329, 473. W. B. Saunders Co., Phila- delphia. 59 SiMITH, R. E. 1907. Report of tlie plant pathologist. Walnut blight investigation. California Agr. Exp. Sta. Bui. 184:232-236. 3 fig. so Smith, R. E. 1909. Report of the plant pathologist. Walnut blight and culture. California Agr. Exp. Sta. Bui. 203:24-32. fig. 7-12. 6i Smith, R. E., and E. H. Smith. 1911. California plant diseases. California Agr. Exp. Sta. Bui. 218:1039-1193. fig. 102 62 Smith, R. E., C. O. Smith, and H. J. Ramsey. 1912. Walnut culture in California. Walnut blight. California Agr. Exp. Sta. Bui. 231:119-398. 96 fig. 63 Smith, R. E., T. Francis Hunt, and W. H. Nixon. 1913. Spraying walnut trees for blight and aphis control. California Agr. Exp. Sta. Cir. 107:1-8. 64 Smith, R. E. 1927. The walnut blight story to date. Pacific Rural Press 113(3) :71, 78. 1 fig. es Smith, R. E. 1927. Can walnut blight be controlled? Diamond Walnut News 9(5) :4-6. 9 fig. 66 Stapp, C. 1928. Schizomycetes (Spaltpilze oder Bakterien). In: Sorauer, P. Handbuch der Pflanzenkrankheiten. 5th ed. 2:74-77. 2 fig. Verlagsbuchhandlung Paul Parey, Berlin. Bul. 564] Bacteriosis of the Engltsii Walnut 87 «7 Van Poeteren, N. 1923. Verslag over de werkzaamheden van den plantenziektenkundigen dienst over het jarr 1922 [Report on the activities of the phytopathological service in the year 1922.] Verslag. Med. Plantenziektenkund. Dienst Wageningen 31:9. 68 Waite, M. B. 1914. The diseases of nut trees. North. Nut Growers Assoc. Rept. 4th Ann. Meet, p. 50-61. 69 WORMALD, H. 1927. Notes on plant diseases in 1925. East Mailing Res. Sta [Kent] Ann. Rept. 1925(March):76, 85-86. 70 WOEMALD, H. 1927. Walnut bacteriosis. East Mailing Res. Sta. [Kent] Ann. Rept. 1926 (May):59. 71 WORMALD, H. 1928. Plant pathology. East Mailing Res. Sta. [Kent] Ann. Rept. 1927(May) : 55. 7 - WORMALD, H. 1928. Notes on plant diseases in 1926. East Mailing Res. Sta. [Kent] Ann. Rept. 14th and 15th years. II Supplement. (Oct.) p. 75-88. 73 WORMALD, H. 1930. Bacterial "blight" of walnuts in Britain. Ann. Appl. Biol. 17(l):59-70. lpl. 74 WORMALD, H. 1930. Bacterial blight of walnuts. Gard. Chron. 3rd Ser. 88(2281) :216-218. 3 ng. APPENDIX TO BIBLIOGRAPHY Brief reports of the disease have appeared from time to time in the Plant Disease Reporter it These reports frequently are unsigned, and it has been found more con- venient to list them chronologically under the name of the publication and its sup- plements rather than by author. 75 pi. Dis. Bul. 6(10) :159. 1922. 85 pi. Dis. Bul. Sup. 20:135-136. 1922. 76 PI. Dis. Rep. 12(7) :81. 1928. 86 pi. Dis. Bul. Sup. 28:391. 1923. 77 PI. Dis. Rep. 12(8) :92. 1928. 87 pi. Dis. Rep. Sup. 33:146. 1924. 78 PI. Dis. Rep. 12(12) :137. 1928. 88 pi. Dis. Rep. Sup. 47:296-297. 1926. 79 PI. Dis. Rep. 13(2) :22. 1929. 89 pi. Dis. Rep. Sup. 52:107. 1927. so pi. Dis. Rep. 14(14) :132. 1930. oo pi. Dis. Rep. Sup. 60:222. 1928. si PI. Dis. Bul. Sup. 1 :41. 1919. oi PI. Dis. Rep. Sup. 70 :256. 1929. 82 PL Dis. Bul. Sup. 5 : 178. 1919. ^ pi. Dis. Rep. Sup. 75 :39. 1930. 83 PI. Dis. Bul. Sup. 9:179. 1920. os PI. Dis. Rep. Sup. 76:91. 1930. 84 PI. Dis. Bul. Sup. 14:113. 1921. 27 A mimeographed pamphlet issued by the Bureau of Plant Industry, U. S. Dept. Agr. Early issues of this publication appeared under the name Plant Disease Bulletin. 88 University of California — Experiment Station ADDENDA 94 Hamond, J. B. 1931. Some diseases of walnuts. Section IV. Eeport on plant pathology, mycol- ogy and bacteriology for years 1928-1930. East Mailing Ees. Sta. [Kent] Ann. Eept. II Supplement 1928-1930 (Apr.) : 143-149. os Horne, W. T., E. O. Essig, and W. B. Herms. 1923. Plant disease and pest control. California Agr. Exp. Sta. Cir. 265:1-104. Revised 1925, 1927, and 1930. 96 Miller, P. W. 1932. Second report of progress on walnut blight and its control in Oregon. Oregon State Hort. Soc. 23rd Ann. Kept. p. 123-135. 97 Miller, Paul W. 1932. Walnut blight and its control in Oregon. Phytopath. 22(12) :1000. as Miller, P. W. 1933. Walnut blight and its control in Oregon. Oregon State Hort. Soc. 24th Ann. Kept. p. 140-161. 1 fig. 99 Rudolph, B. A. 1930. On the control of bacterial blight of walnuts. Phytopath. 20(10) :856. ioo Rudolph, B. A. 1931. Spraying for walnut blight control. Pacific Rural Press 122(26) :590, 594. 3 fig. ioi Rudolph, B. A. 1932. Bacterial blight of walnuts and its control. Diamond Walnut News 14(1) :4-6. 3 fig. 102 Rudolph, B. A. 1932. The preparation of bordeaux spray for walnut blight control. Diamond Walnut News 14(1): 8-9. 103 Rudolph, B. A. 1932. Walnut blight and its control. California Cultivator 78(4):78-79, 91. lfig. 104 Rudolph, B. A. 1933. Bacteriosis (blight) and its control. Diamond Walnut News 15(1) :9- 10. 3 fig. ion Rudolph, B. A. 1933. Essentials of making bordeaux spray for control of blight. Diamond Walnut News 15(1):10-11. ioc Rudolph, B. A. 1933. For control of walnut "blight." Pacific Rural Press 125(6) :95. 2 fig. 107 WORMALD, H., AND J. B. HAMOND. 1931. The distribution of bacterial blight of walnuts. Card. Oliron. 3rd Ser. 90(2348) :476-77. 3 fig. 18wi-2,'34