AGRICULTURE LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN no. 338 - 353 NOTICE: Return or renew all Library Materials! The Minimum Fee for each Lost Book is $50.00. The person charging this material is responsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for discipli- nary action and may result in dismissal from the University. To renew call Telephone Center, 333-8400 UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN 1116 05 1999 L161 O-1096 UNIVERSITY OF ILLINOIS Agricultural Experiment Station BULLETIN No. 340 EXPERIMENTS WITH BLISTER CANKER OF APPLE TREES BY H. W. ANDERSON URBANA, ILLINOIS, JANUARY, 1930 CONTENTS PAGE ECONOMIC IMPORTANCE OF BLISTER CANKER 55 HISTORY AND DISTRIBUTION 57 LIFE HISTORY OF THE FUNGUS 58 Spore Germination 61 Dissemination of Disease 61 How Inoculation and Infection Occur 63 INFECTION EXPERIMENTS 63 OBSERVATIONS AND EXPERIMENTS ON THE ORIGIN OF CANKERS : 65 Development in Host Tissues 71 Cause of External Fruiting 73 INFLUENCE OF ENVIRONMENT AND TYPE OF GROWTH ON PREVALENCE OF BLISTER CANKER 75 EXPERIMENTS ON CONTROL OF BLISTER CANKER 79 Plan of the Experiment 80 Methods Used 80 Tools Employed for Excision 81 Excision of Cankers 82 Wound Treatment Experiments 84 Results of Excision Experiments 85 Results in Check Orchards 86 Experimental Work on Removal of Cankered Limbs 88 SUMMARY AND CONCLUSIONS 88 RECOMMENDATIONS FOR CONTROL.. 89 EXPERIMENTS WITH BLISTER CANKER OF APPLE TREES By H. W. ANDERSON, Associate Chief in Pomological Pathology An investigation of the life history of the fungus causing apple blister canker was initiated in 1917, but before sufficient progress had been made to warrant publication, the comprehensive investigations of Cooper 1 were published. As a result, this phase of the investigation was discontinued and stress was laid on control measures. No one had determined whether excision 2 of the cankers and removal of dis- eased limbs in an orchard over a period of years would successfully prolong its productive period. This phase of the subject received the major emphasis and as a result a popular circular was published in 1922, 3 giving the grower the methods employed in the investigations together with general advice on the care of the orchard to prevent infection. The purpose of the present publication is to give the data on which the former publication was based and to present additional facts resulting from a continuation of the investigations. During the eight years covered by this experiment, certain facts in regard to the etiology of the disease and the environmental factors inducing canker development were secured and will be here recorded. ECONOMIC IMPORTANCE OF BLISTER CANKER The loss from blister canker consists almost entirely of the direct elimination of bearing surface, altho there is some evidence that trees in which the disease is established thruout the wood are thereby weak- ened and bear inferior fruit. Observations of the author have shown that diseased trees, where external cankers are not present, are equally productive with those not diseased, and it is only when a limb is almost completely girdled by a superficial canker, that the apples become inferior in quality. Wood infection in no wise stunts the growth of the tree. Since limbs and entire trees are killed during their most produc- tive period, it is evident that heavy losses must result when this dis- ease is prevalent in an orchard (Fig. 1). Most of the loss in Illinois at present is confined to a few susceptible varieties, such as Ben Davis and Gano. In orchards planted to these varieties, it is estimated that 'Cooper, J. R. Studies of the etiology and control of blister canker on apple trees. Nebr. Agr. Exp. Sta. Res. Bui. 12. 1917. 'The term "excision" is used in this publication to designate the process of removing bark in the diseased area and does not imply the removal of dis- eased wood or the eradication of the canker. 'Orchard practice for the control of blister canker of apple trees. 111. Agr. Exp. Sta. Circ. 258. 1922. 55 56 BULLETIN No. 340 [January, 10 percent or more of the bearing wood is unproductive as a result of blister canker. Other varieties suffer no appreciable loss, altho blister canker may be found to a limited extent on most of our stand- ard varieties. The greatest loss by far results from the early decline of Ben Davis plantings. An orchard of this variety soon becomes so badly diseased that it is no longer profitable to care for the straggling trees (Fig. 2). The average life of a Ben Davis in Illinois is about twenty-five years, while orchards planted to other varieties are at their maximum period of production at this age. Where alternate blocks of Ben Davis and other varieties are planted, the loss of the FIG. 1. A COMMON SIGHT AROUND AN OLD BEN DAVIS ORCHARD All these limbs and many more were removed on account of blister canker. trees in the Ben Davis rows is especially serious since the owner rarely replants and the orchard is retained on account of the nonsuscept- ible varieties, thus resulting in a waste of valuable space. In one county during the past four years about 50,000 trees have been removed largely because of blister canker. Most of these or- chards were less than thirty years old. Fifty-year-old Ben Davis trees bearing excellent crops have been observed, and there is no reason why orchards of this variety could not be producing after half a century were it not for this disease. It is rare to find a Ben Davis orchard over thirty-five years of age and if found, it is seldom profitable because of the numerous missing or crippled trees. To no other cause than blister canker can the early decline of Ben Davis orchards in this state be ascribed. Ben Davis and Gano constituted 30 percent of the bearing apple trees of Illinois in 1920. Owing to the nature of the disease, it is impossible to calculate the exact financial loss, but it is evident that it must be very great. Fortunately the younger orchards are not so heavily planted to these varieties, and the loss 1930] APPLE BLISTER CANKER EXPERIMENTS 57 will decrease after the present old orchards are moved. 1 On the other hand, new varieties of recent introduction have not been subjected to adequate tests to determine their resistance to this disease, so that there is a possibility of future heavy losses if care is not taken to follow correct cultural practices. HISTORY AND DISTRIBUTION A detailed history of apple blister canker in America is given by Gloyer 2 and others and need not be repeated here except as to its FIG. 2. AN ADVANCED STAGE OF BLISTER CANKER It is doubtful if a tree such as this will produce enough to justify saving it. bearing on Illinois conditions. The disease has been known to occur on the apple since 1831, when Schweinitz first described the fungus, but it was not until 1900 that its serious nature in the Middle West was recognized. Hasselbring 3 observed the disease in Illinois orchards 'Ben Davis is still recommended for the river bluff sections of western Illi- nois (see 111. State Hort. Soc. Trans. 62, 33. 1928), and there it is being planted by progressive fruit growers in preference to the newer varieties. 2 Gloyer, W. O. Blister canker of apple and its control. N. Y. (Geneva) Agr. Exp. Sta. Bui. 485. 1921. 'Hasselbring, H. Canker of apple trees. 111. Agr. Exp. Sta. Bui. 70. 1902. 58 BULLETIN No. 340 [January, during the summer of 1901 and first called attention to the parasitic nature of the fungus and the fact that it was the real cause of the death of many apple trees. He gave a good description of the symp- toms of the disease and observed the penetration of the mycelium into the wood, a fact of fundamental importance when control meas- ures are considered. He gave little information concerning the history of the disease in Illinois. Older fruit growers interviewed by the writer all stated that blister canker has always been a serious problem in Ben Davis orchards. Since this variety was introduced into the state shortly after the Civil War, it is probable that the disease has been present in com- mercial orchards since that time. There is every reason to believe that it was to be found on several wild hosts, including wild crab and mountain ash in the neighborhood of the cultivated apple trees, previous to this time and only awaited the appearance of a susceptible variety to become destructive and generally distributed. Blister canker is more prevalent and destructive in southern than in northern regions, but is found in all sections of the United States east of the Rocky mountains. It seems to be more destructive in the drier regions of the Great Plains than in the comparatively moist regions of the central and eastern states. The fungus causing blister canker, Nummularia discreta (Schw.) Tul., has been found on a number of woody plants such as June berry (Amelanchier canadensis) , mountain ash (Sorbus americana and S. hybrida), honey locust (Gleditsia tricanthos), white birch (Betula alba), white elm (Ulmus americana), redbud (Cercis canadensis), and magnolia (Magnolia glauca), as well as various species of Malus. It is reported to occur on pear, but has not been observed on this host in Illinois. It is common on apple and mountain ash in this state and has been observed on honey locust and elm. The disease is of economic importance only on the apple. LIFE HISTORY OF THE FUNGUS In order to make clear the nature of the problem involved in the experimental work, it is necessary to present certain facts in regard to the life history and habits of this organism. No attempt is made to present all of the experimental work on which these facts are based. Where the writer has arrived at conclusions at variance with other investigators, a more detailed discussion is presented. The fungus causing blister canker is an Ascomycete, Nummularia discreta (Schw.) Tul., and like most fungi of this group has two types of spores conidia and ascospores. The conidia are produced in lenticular fruiting bodies, usually distributed over the new part of the canker. The outer covering of the lens-like structure breaks and the 1930} APPLE BLISTER CANKER EXPERIMENTS 59 edges roll back forming a star-shaped opening and exposing the honey- colored masses of conidia which are produced over the entire inner surface of the fruiting body (Fig. 3, a). Thus the rolled-back seg- ments carry the spores into the open, where they can be easily scat- tered. While these spores may produce infections, their role in the life history of the fungus is not important and will be disregarded in the subsequent discussion. FIG. 3. SPORE STAGES OF BLISTER CANKER (a) "Blisters" with rolled-back edges exposing dust-colored masses of spores; (b) "nail heads" of perfect or winter stage. Mottled inner bark with black rings of sectioned blisters is shown at c. The other spore stage is produced in the upper layer of the "nail heads" which characterize this disease. 1 (Fig. 3, b). Both conidia and ascospores may be found in the same canker, but many cankers can be found with only the conidial stage, which is always produced first. That it takes at least two years to produce 'For a complete discussion of the symptoms and a description of the fungus, see Circular 258 of this Station, already referred to. 60 BULLETIN No. 340 [January, the ascospore stage is evident from numerous observations made on excised cankers and on new cankers over a period of years. In the experimental orchard described later, about 100 cankers were excised in February and March, 1919. They were examined in October, 1919, and again in March, 1920. In late August, 1920, con- siderable advance of the cankered area had occurred but no fruiting bodies were found. In a neighboring orchard a number of cankered areas were marked as doubtful blister canker in March, 1919. These were examined several times during the summer of 1919. In July, 1920, a few of these had developed conidial fructification, but it was not until the late summer of 1920 that any ascospores were produced on these cankers. This point is important in the control of the disease. If a canker is excised one year, it may be safely left for two seasons with- out danger of ascospore production, altho as pointed out later, it is best to make annual surveys of the orchards. The ascospores are ordinarily mature and discharging during the months of July, August, September, and October. Mature viable ascospores, however, may be found at any other time of the year, both in the perithecia and on the surface of the stromata. During periods when ascus production is not active, the perithecia are found crowded with ascospores freed from the asci. These evidently would not be discharged from the perithecium, but they might escape by the wearing away of the surface of the stromata, which occurs within a relatively short time after the greater portion of the ascospores are discharged. Discharge of ascospores takes place only when the bark is well soaked with water. Glass slides placed over the stromata on limbs in the orchard were examined at regular intervals during the summer of 1918 at Centralia, Illinois. It was found that very few ascospores were obtained except at intervals of two to three days fol- lowing a heavy rain. Usually a day elapsed before discharge began, but occasionally it was initiated within twelve hours. Many mature perithecia were observed which did not discharge ascospores. The exact cause of this is not evident. A continuous supply of ascospores for infection is provided in several ways: (1) not all ascospores mature at one time in a single perithecium; (2) not all perithecia are in the same stage of develop- ment even in a single stroma; (3) when discharged, not all asco- spores are carried into the air or washed from the surface of the canker. In some cases all the discharged spores are prevented from reaching the outer air by a thin membrane covering the surface of the saucer-like stroma. The masses of purple spores may be seen, with the naked eye, heaped about the ostiole of the perithecium. Gloyer 1 has shown that on a single limb of mountain ash about a foot in length, on which there were 88 stromata, at least 350 million *N. Y. (Geneva) Agr. Exp. Sta. Bui. 485, 39. 1921. 1930] APPLE BLISTER CANKER EXPERIMENTS 61 spores were exposed at one time. In attempting to wash these off, it was found that only a limited number could be washed off at one time, and that each washing over a period of weeks removed several hundred thousand additional spores. Thus, at all times, in an orchard where ascospores are being produced, there is an abundance of inoc- ulum for infection. Spore Germination While conidia germinate with difficulty and soon lose their via- bility, the ascospores germinate easily and retain their viability over at least a year. Ascospores on a limb left on an outside window ledge in October of 1918 germinated the following October. Stromata were collected from a pile of branches which had been left in an orchard for three years and from these, viable ascospores were readily ob- tained. The date when these ascospores were formed was uncertain, but it is probable that they were at least a year old before the limbs were cut. Stromata collected and placed in a vial showed viable asco- spores eight months later. Dissemination of Disease Observations and experiments over a period of ten years failed to give conclusive information concerning the methods of dissemination of the fungus, altho there seems every reason to believe that ordinary agents are operative. In the early part of these investigations, before the uncertainty of infection was realized, a number of experiments were tried to determine methods of dissemination. These resulted in failures, none of the inoculations, however made, producing infection. Ants, bees, flies, woolly-bear caterpillars, and various undetermined insects were found to retain ascospores on their legs after walking across a number of damp stromata on which ascospores were abund- ant. A finger pressed against a mass of the ascospores retains thous- ands of these, and man is probably responsible for a general dissemi- nation of the ascospores during the various operations about the orchard. The sawdust between the teeth of a pruning saw was cul- tured in 1919 and found to yield the organism, but the chance of infection by this means is probably far less important than by natural means. Water carries enormous numbers of spores from cankers to lower limbs, but since infection in a tree is general by the time the cankers produce ascospores, this fact is of little importance. It is evident, from observations as to the initial infection, that many of these take place near the top of the tree or far out on the branches, and that spores that are washed down the limbs play no part in such infections. Shortly after the spores become massed on the surface of the stromata, they become dried, and later the whole surface weathers away. The spores actually discharged into the air, and those resting on the 62 BULLETIN No. 340 [Januai oe@*oooooooeooeoeo " oe@oooooo*oo**o* oooooo@oooo*ooo eooo@ooe**oe oooooo*ooeee e@oeeeoooooeooooooo< oooooooooooooooo0o*oepoeo oooooooooo*oo*oooogoo*o** oooooooooo*o*ooooop*opoo ooooooooooooooooooeeooboe ooooooooooooooooooooooooo ooooooooeoooooooooooooooooo OOOOO*OOOOOOOOOOOOOOOOOO0ft* OOOOOOOOO0OOOOOOOOOO@OOOO oooooooooooooooooooeoeeeeo o@ooooooooooooooooooo oooooooooooooeoooope0ooo oo0oooooooooooooooeopeoooo ooooooooo*ooooo*ooo*5ooeooo ooooooooooooooeooooeoo ooooooooooooooooooooo*oo oooooooooooooooooo$o*oooe ooooooooooooooooooi5**oo ooooooooooooooooeooooooooooo oooooooooo*ooooooooo*oooo ooooooooooo 00000*00000000 oooooooooooooooo@oooeooooo oooooooooooooooooooooooo* oooooooooooooooooooooooooooo OOOOOOOOOOOOOOOOOOOOOOO0OOO* ooooooooooooooooooooeoooeooo ooooooooooooooooooooeoooeo ooooooooooooooooooooooooooo ooooooooooooooooooooooooooo eooooooooooooooooooooo*oooo 00000000000000000000000*0000 OOOOOOOOOOOOOOOO0OOOOOOOOO* ooooooo@ooooooooooooooooooo oooooooooooooooooooooooooo ooooooooooooooooooooooooo*o ooooooooooooooooooooooooooo* oooo@oooooooooooooooooooooo oooooooooooo*oooooo*ooooooo . ooooooooooooooooooooooeo*e*o o@ooooooooooooooooooooooooo ooooooooo@oooooooooo*oo*ooo F!G. 4. -DIAGRAM or LxptRincNTAL. ORCHARD , CARRY, IUJNOO O Healthy tree 1921 1923 1925 & 1926 Infected prior to 1921 1922 192.4 19Z7 1930] APPLE BLISTER CANKER EXPERIMENTS 63 surface of the weathering stromata, may be carried by air currents to other trees. That these spores rarely find conditions suitable for infection is evident from the comparatively slow spread of the disease. The location of diseased trees in an orchard indicates that the chances of infection in the neighborhood of ascospore-producing can- kers are greater than in remote portions of the same orchard. The grouping of diseased trees in the accompanying map (Fig. 4) of a typical orchard indicates this. On the other hand, the occasional scat- tered infections in this orchard can be explained only by assuming that the spores may be carried a considerable distance by air currents or other agents, but that the chances of infection are inversely propor- tional to the distance from the source of inoculum. Clustering of in- fections in an orchard may be explained in part by soil conditions, but this is by no means always true. Since the maximum number of spores are on the surface of the stromata during harvest time, it is probable that the pickers play some part in disseminating the spores. At this time, also, broken limbs resulting from the weight of the fruit and carelessness of pickers are so general that chances of infec- tion are exceptionally good. How Inoculation and Infection Occur Infection takes place only on the "wood" of the tree, never on the fruit, leaves, or current season's growth. Repeated attempts by the writer to produce infection by inoculations on the unwounded surface, in the bark, cambium, and young xylem have always re- sulted in failure. This has also been the experience of other investi- gators, so that it may be stated with certainty that natural infection is always in the xylem or wood of the tree. Cooper 1 has produced artificial infection with both conidia and ascospores in the cambium of older limbs, but the percentages of success were low. He shows further that in two-, three-, and four-year-old wood the percentage of infection is much greater. The numerous experiments of Gloyer and Cooper indicate that infection takes place only where the spores are protected from drying and where continuous moist conditions pre- vail. Such conditions were produced by boring holes in the limbs and, after inoculation, covering the wounds with grafting wax, or with cloth coated with paraffin or grafting wax or both. While under these conditions infection with conidia could be easily produced in wood, it is evident that natural conditions are not simulated. INFECTION EXPERIMENTS Attempts were made to determine whether infection could occur on new and old pruning wounds where no protection was afforded. 'Nebr. Agr. Exp. Sta. Res. Bui. 12, 16. 1917. 64 BULLETIN No. 340 [January, These experiments were made under conditions favoring infection by the fungus, but owing to the fact that trees of a susceptible variety were not available in quantity, only a limited number of inoculations were possible. At Barry in 1920, in August and again in September, inoculations were made on 34 trees of nineteen-year-old Ben Davis in a block of this variety which up to that date had not showed evi- dence of blister canker either in the appearance of cankers or of slime- flux from the wounds. The owner had pruned the trees a few years before, removing a number of large limbs. In 1919 a few more limbs had been cut off, and a few days previous to the first series of inocu- lations, ten limbs varying in age from two to six years were removed. No attempt was made to sterilize the wounds, since any disinfectant applied to the surface would have soaked into the cut surface and thus vitiated the experiment. The inoculum was secured by crushing in rain water a large num- ber of stromata containing perithecia from which ascospores were shooting. A soft brush was used to distribute the spores over the surface of the wounds. The wounds were then covered with several layers of paper towels soaked in water. Since the weather was cloudy at the time of inoculation, these coverings remained damp for two days and were then removed. The total number of inoculations was 132, ten of which were made on recently cut wounds and the re- mainder on wounds of at least one year of age. Very little cracking of the wood was observed in these wounds. Where it did occur, efforts were made to force the inoculum from the brush into the cracks. These inoculated trees were watched from 1920 until 1927, since it was realized that infections may take several years to appear externally. Of the 34 trees thus inoculated, only one showed evi- dence of canker in later years. In 1924 one tree developed a canker near the top. The limb was removed and the infected wood traced. No evidence of any connection with the inoculations could be found. In 1926 four limbs were removed where inoculations had been made on branches from these limbs, and cuts were made across the limbs near the points of inoculation. No evidence of infection could be found. These infection experiments were too few in number and made over too limited a time to draw any safe conclusions, but they do indi- cate that infection thru even large pruning wounds is not common. One could surmise this from observation, since thousands of pruning wounds made in this same orchard and exposed to infection over a period of years, resulted in comparatively few diseased trees. Another series of inoculations was made on four twelve-year-old Ben Davis trees at Urbana in 1918. The results of these experiments bear out those obtained by Glover and Cooper and need not be given in detail. Forty wounds made by inserting ascospores, conidia, and pure cultures of the fungus under the bark, resulted in no infection. 1930] APPLE BLJSTEB CAXKEB EXPERIMENTS 65 These wounds were all cut out the following spring and no growth of the fungus into the surrounding tissue was observed. Ascospores placed on an old pruning wound covered with waxed paper and then with grafting wax gave a positive infection, but this did not become evident until two years later (1921). Seven attempts to infect newly cut stubs in the same manner resulted in failures. A broken stub in the top of the tree was also inoculated and covered. Infection occurred in this case, but there was no external evidence until 1921, when a canker appeared around a wound two feet below the point of in- oculation. The infection was traced in the wood to the point of inocu- lation. At various times during the past ten years additional infection experiments were carried out, but the results were negative and gave no additional light on the conditions favorable to infection except that they indicated the difficulty of producing infection by super- ficial inoculations. Attempts were made to produce natural infection by sawing first thru a cankered branch and then thru a healthy branch or stub. The number of such trials was limited, owing to the fact that the work had to be done in a commercial orchard. Seventy-four such cuts were made where the limbs used were alive and from three to seven years old. Eighteen were made on limbs that had died from various causes, mostly from being shaded by higher branches. Active cankers were selected, and after the diseased limb was removed, sawdust was moist- ened and placed between the teeth of the saw. Three of the trees so inoculated developed cankers within the next six years, but in no case could the infected area be traced to the limbs removed altho one was so generally diseased as to render the point of primary infection doubtful. In the face of these generally negative results it would appear that statements to the effect that large pruning wounds result in infection are to be discredited. However, where conditions are par- ticularly favorable, as when there is cracking and subsequent inocu- lation followed by closing of cracks thru a prolonged wet period during the critical time for infection, it is not at all improbable that such wounds may be responsible for infection. OBSERVATIONS AND EXPERIMENTS ON THE ORIGIN OF CANKERS From 1917 to 1928 a study was made of blister canker in the Ben Davis orchards of this state. Surveys were made of four large or- chards, including a total of over 10,000 trees. From 1919 to 1928 more detailed observations were made of the orchard in which the experimental work on canker control was carried out. During the course of this work each one of nearly 1,600 trees had to be carefully BOJJOTX Xo. 3*1 and, wime cankered, the extent of the cankered area had to be defeenmnoL These extensive field observations gave an opportunity to study the conditions under which natural infection occurs. When the study was initialed, it was thought that the external canker indi- cated the point of infection, but it was soon realized that this is by no means always true. In fact, huge cankers are rarely formed about the primary point of infection. In makmg these examinations, it was necessary to have a method for distinguishing betmeen infected and uninf ected wood. Cooper 11 sections of the infected wood and stained the fungus to deter- course. This method was considered too laborious for the It was found possible to secure cul- tures off the blister canker fuugua from small blocks of the infected wood, and this method was used until the writer had become so fioJBiM ilh Ifci il lui iii nf ili i ii nl 1 Ihni hi fill ju lifinl in *"**iKitinTnof the ^nitnral method. At first a large number of cultures were made from diseased wood on agar plates. The agpr used was a prune agar with lactic acid added to diHUMiage bacterial growth. The mycelium of \*mmmlaria discrete in this medium is characteristic, and it was possible to make determi- nations with ease where the wood was sufficiently isolated from ex- ternal aumcca of i iiii iCMiHtt were obtained in aD the cnltnres. The presence of sfime-vkrx mdication of blister canker, as evidenced by this similar experiments and ooservatBons. These iDustiations indicate the iinjililj of the the origin of infection in the H. " ..-. ..__"*'. , ,__ was not always possmte to oetcf - point of infection, since the trees would tone had to be severely crippled by numerous cuts but. when possible, suftoent cuts were made to drttirmmr the extent of the diseased tissues. Ouwy those trees were used on which not more than one or two cankers were found and those in such a position m to allow the fimbs to be cut off witiftont 'seriously injuiiwi, the trees. In a number of cases entire trees badly cankered were cut down and fimbs sawed off at various points to *V*^ **> the cihjwl off the diseased area. In every case it was found that the disease wasyanilly the larger branches and usually extended to near the fop off the top- most branch. In some cases the three- and four-year-old showed no evidence off - ::' -_"^7 L~":~~.: :.., i.-:.-. :e: ..*?-.. ~ m tfce loor looc VDBI^BK Buun OKUBCDES with A finiobBd BHBHMSF off Fig. 10| r wfcflc the tan it the Omofc portion, vine 'i i_-,i: type. 1 iliiilj ii f IhjM Ijpm iiiiahii 111 fill lint eaniDEEft ocennBu m trees nawnv? a am ~*~ "* * ~ ; *.-- - . _ _ _ . . : . . .__ "j."ne pid'alenoB of cankers m trees of this type is not related to Ike ^pjar off the tae, omee amne wrj ^aemmm central-deader trpe aie to be foond m the area wfcei Inn of the other type are conmmn- The iBMBm for OB abomdance of cantos and their tan of the m^eht. type may be explained m part by the fact r.rf. "~ :r_i>.i.iTi. :ri_:i^ ::^-.LL :f '"7" 7i--_/ JL :,:,_f .,-* - - _ m ... S_^^_JS__ ^J " _ giving cnances tof uueFuon. ano nBDnaau unc sapwou on. mes right branches is Toy Aim M emptied with that at a c EXPERHTEMTS OM COMTROL OF BUSTER CAJTKER The object of tiub phase of the e^petiantel wk was to de- termine whether it is possible to reduce the niBher of diseased inn :, -_ - - 1_^.. ^ "" - .... wrmcn exc^sHm nas ueen uKacu^cu VBCUWT UHC " B TB M MIMlMLM^ - - II B^^^ ^W^J^^ m mxucn exnanni nas nm neen pnE _ .^^iJt - ' - *. B J ^ a imuLiion. resom was BBBHOI on me lister canker otcui&. the diseased trees aie tnig a alaw nit Ml from a center of s not iin that nifeetiiom is KoBated dfiseased trees m an orehaid- How- CRg. 4> dhowm on page fe of cfeeased lujuk do OULIH abont at olated diseased inn aone not B Boamrir Siom asoosDove nvocniaiDonKi vie pvodntomi was caKnual j :r 80 BULLETIN No. 340 [January, for the success of the experiment. For this reason it was impossible to leave check trees in the same orchard where the experiments were performed. This was recognized as a weakness in the experimental work, but since neighboring orchards of the same age, on the same type of soil, managed by the same man were available, this weakness was not considered a serious one. Plan of the Experiment The orchard selected for the experiments on control of blister canker is located one and one-half miles southwest of Barry, Illinois. It consists of a solid block of 1,520 trees of Ben Davis. The orchard was planted in 1898, so that at the beginning of the experiments in 1919 the trees were twenty-one years old. They had made a good growth and were in excellent condition at the time the experiments were started. Very little pruning had been attempted until the year 1915-16, when a number of the lower branches and some higher in the trees were cut out. The upper ones were removed following breaking caused by an unusually heavy crop of fruit. The branches removed were usually quite large, that is, exceeding one inch in di- ameter. The manager labored under a mistaken idea that the branches should be sawed, leaving a stub twice the length of the di- ameter of the branch removed. This resulted in leaving numerous stubs and much exposed wood surface. This orchard was selected for the following reasons: (1) the canker had not established itself to such an extent that control meas- ures were deemed impractical; (2) the trees were of the age at which this variety usually begins to develop canker; (3) an orchard of the same age and variety and under the same management bordered the experimental block. Methods Used Some fundamental facts in regard to the control work were recog- nized before this experiment was started, and these need to be em- phasized at this time: (1) Not all infected trees had evident cankers, so that 100-percent elimination of cankers the first year w r ould not mean that cankers appearing the next year on new trees were the result of infection following the excision of the cankers. (2) A few new infections could be expected from outside sources, especially from two neighboring orchards used as controls. (3) The excision of cankers did not imply elimination of the disease in the tree nor a guarantee that new cankered wood would not appear outside the excised cank- ered, area. However, during the first three years, after cutting out a canker the wound and tools were sterilized and the wood was painted later in the season by the manager. After the first three years no attempt was made to sterilize either the wounds or the tools, since the futility of such procedure was realized. The wounds were always 1930} APPLE BLISTER CANKER EXPERIMENTS 81 cut back to healthy bark because it was observed early in the experi- ments that in some cases callus is formed about the edge of the wound and may continue healthy for several years, thus prolonging the life of the limb. Also, the insects commonly found in the dead bark along the edge of the cankers were absent. At first, shellac was used to cover the wounds before painting, but this was discontinued on account of the extra labor, altho it is still recommended. Since it was felt that the success of this plan of blister canker control must be made practical, all operations not essential to the successful re- duction of the canker were eliminated. A series of preliminary experiments on wound treatment were tried in 1919, partly with the hope that a substance could be found which would prevent the extension of the cankered area over a period of years and thus reduce the labor. Furthermore, these experiments were designed to indicate whether or not standard methods of wound treat- ment would prevent the ultimate extension of the cankers. FIG. 13. Two TOOLS USEFUL IN CUTTING OUT CANKERS, A FARRIER'S KNIFE AND A CHISEL Other experiments were designed to answer the question: Can blister canker be entirely eliminated from a tree by removing cankered limbs in an early stage? Certain trees were selected which had single cankers near the top of the tree or far out on side branches, and the entire limb was removed or the cut was made far enough below the canker to be reasonably certain that all diseased wood was removed. Tools Employed for Excision At first a rather elaborate set of tools was carried to operate on the trees, but after two years' experience these were reduced to two instruments, a farrier's knife and a good pruning saw. Limbs too large to be cut with a pruning saw were marked and were later removed by workmen using a crosscut saw. The farrier's knife is the most useful instrument for this work, but it should be of a very good quality steel and should have the curved end ground down until a right-angled bend is secured rather than a hook (see Fig. 13). A -2 BrLLEnx Xo. 310 [January, small drawknife is useful and permits rapid work, but if the ferrier's knife is kept sharp, it serves the same purpose. At the start a map of the orchard was prepared and a number of blue line prints from a Tan Dyke negative were made (Fig. 4). The trees were given numbers and all diseased trees were marked after each survey. The map was carried during the survey, together with the notes of the previous year. Since the number of cankers and their genera] location were given in these notes, it was possible to locate any new cankers on old diseased trees as well as on newly diseased trees. Excision of Cankers Experience is necessary in locating cankers that have not fruited. It was found that the mottled bark was the only reliable indication of canker in the absence of fruiting bodies. In an old orchard where numerous other cankers are to be found, the ability to distinguish blister canker is essential to the success of this program of control. The experience of the writer has been that most orchardists never become skilled enough to locate all cankers, but since the program of control allows excision after the formation of stromata, the im- portance of earlier location of the cankers is minimized. As a rule, the orchardist should employ someone who has had a long experience in this line of work since an unskilled worker rarely locates more than half the cankers. In the orchard adjoining the experimental orchard, the author followed workmen who had helped in the first year's work, and found that approximately 50 percent of the cankers had been overlooked. No attempt was made to destroy the fruiting bodies removed from the canker during the first year's operations. It was realized that there was a possibility of these discharging spores while lying on the ground,, but there seemed to be no practical way of catching all the excised bark since it was very brittle and would fly in all directions when cut. Since the cankers were cleaned out the second year and in subsequent years before the fruiting bodies were formed, the chance of infection from the removed materials existed only during the first year. A preliminary treatment of the cankers with a strong fungicide, such as copper sulfate. to kill the spores would probably have reduced the danger of reinfection, but some preliminary experiments in 1918 indicated that this method was unreliable as an orchard practice. An effort was made to see that no particles of bark remained in the limb crotches below where the cankers were excised. Aside from this, no precautions were taken. The first operation in excising the cankers was to cut out all the dead area down to the wood. This can be done rapidly by using the farrier's knife much as one would use a drawknife. After all the dead bark was removed, a stripe was cut about the edge of the canker 1930] APPLE BLISTER CANKER EXPERIMENTS 83 so that healthy bark completely surrounded the wound. The entire wound was then sponged with a solution of mercuric chlorid and mercuric cyanid with some glycerin added. 1 Except between 1919 and 1921, when the treatment of cankers was under investigation, the owner, later in the year, painted all pruning wounds, and the canker wounds were covered at that time. FIG. 14. RENEWAL OF BEARING AREA ON CANKERED TREE WITH MOST OF MAIN STEM REMOVED If properly pruned, the vigorous new branches developed on such trees will yield paying crops before the entire tree ia killed by the disease. No limb was removed by excision which could be saved for another crop. It took only a few minutes more to clean out a large canker than it did to saw off a limb, and the crop of the following year might be well worth saving. When the limb was within an inch or so of being girdled, no attempt was made to save it, since under such con- ditions it will die before the crop of the following year is matured. Another reason for saving limbs is that the removal of large limbs exposes others to serious sun scald (Fig. 14) . A limb which is destined to die within two or three seasons should have a number of the smaller 'This solution was used after 1923. It consisted of a solution of 1 to 500 mercuric chlorid and 1 to 500 mercuric cyanid, the solvent being equal parts of glycerin and water. This solution has less glycerin in it than the California formula for fire blight control and is much more satisfactory for blister canker' work. Previous to 1923 a 1 to 500 mercuric chlorid solution was used. dhnr the fame L m Fdbraaorr. 191* Aft tin nj; -..:: i 7_L : r i . . " _ -: :O-E woe tnali :: 77-7 :.i.:v i.;.i tte ailiaan of Ike aureat moid bedewiaed. tlwt ?jff ar wftath vitib A brash- - - M tretoelt fribved a irh was aUoved to mica' as faedL dt three eais BBi IT '*** & BBBEOU JB9 Bnr D^TB !' ^r: '^-' TT(itail tuns nM*ni% '. ;'! 1 _- Z . ^*- ll ". -'Ill M !4 :: ;i: : r -r 22.17 -J : .4 : ~ i t : : r 1-91 2-3i -ntunt ji IU515. Tie :r bem "."."- " - t L -: ~_ . i ; 1 r' : :-.- -- .-- 7- -: eke pressure of other work prevented the In 1927 the last sorcvy was to Prior to 1931, 9ft tiu* or CLJ8 percent vac evBdentdhr At the cad of seven jean 337 trees, or 8J7 i* m af> wen Tke percentage of newiy infected trees,, it will he table, im n an d at a iilhii naifana rate, and the enee tatiul fittle finan year to year deqpate the art that the of diseased fnniin m the orchaid wis mm^n grpArgr in. ^"^ of the nvFc^atHBB. "iliii iBiatni lint iiniii lir ojseaaed faces dU not increase the chance of mfcctkav the 86 BULLETIN No. 340 [January must have come from sources outside the orchard, or that the trees that later showed evidence of cankers had been infected previous to the beginning of the experiments. This latter assumption is in line with inoculation experiments reported earlier, where the cankers did not develop until four years after the inoculations. It is probable that FIG. 16. CHARACTERISTIC SECONDARY GROWTH ON A DEHORNED TREE If properly trained, such diseased trees may produce abun- dant crops. The water sprouts should have been thinned and headed back at the proper time. a majority of the cankered trees found during the last three or four years were the result of infections from sources outside the orchard. Results in Check Orchards As stated earlier, it was thought best not to leave checks in the orchard where the experiments were carried out on account of the possibility of infection spreading from these check trees. Across the road from the experimental orchard were 40 acres of Ben Davis and Grimes Golden planted at the same time and under the same management as the experimental block. In the spring of 1919 this orchard was surveyed with the intention of using it for blister canker experiments, but so few cankers were found that it was thought best not to use it. In 1920 there was certainly less than 1 percent of blister canker in evidence in this orchard. About 1921 some cankered 1930] APPLE BLISTER CANKER EXPERIMENTS 87 trees were observed by the manager, and he began to cut out all limbs showing advanced canker but did not cut out the incipient cankers. This orchard, therefore, was receiving better care than the average Illinois orchard, so far as canker was concerned, and was selected as a check on the experimental block. On November 1, 1927, a portion of this orchard was surveyed for blister canker. There is a probability that not all trees that had become infected were observed in this survey, since, as stated above, the manager of the orchard had systematically removed cankered limbs each year since 1921, and thus some trees infected at this time would not yet show canker. Seven hundred fourteen trees were ex- amined. Of these 459 were healthy, to all appearances, and 255 showed disease. Thus the check orchard, starting with less than 1 per cent of diseased trees in 1919, showed 35.7 percent diseased in 1927, while the experimental orchard, with 5 percent of diseased trees in 1919, showed only 22.17 percent in 1927. Furthermore the 1927 figure for the check orchard is a very conservative measure of the amount of infection that had actually taken place in that orchard subsequent to 1919, for the reasons given above. Another and perhaps more accurate check was furnished by a small group of 60 trees belonging to the experimental orchard but separated by a small stream. These trees had been surveyed with the original orchard and the cankers removed in 1919 with the exception of one tree which was to have been cut down but which was not removed as directed. In this block of 60 trees 4 were dis- eased in 1919, or about the same percentage as found in the rest of the experimental orchard at this time. In subsequent years no sur- vey or other work was done on these trees, and on account of their isolation the manager did not give them much care so far as cutting out cankered limbs was concerned. In 1927 a survey was made of these trees and it was found that 36 of the 60 trees, or 60 percent, had blister canker, as compared with 22.17 percent in the experimental block. A comparison of the first check orchard of 714 trees with that of the experimental orchard shows that in eight years there had been an average annual increase of 4.46 percent in the number of diseased trees in the check orchard, as contrasted with an annual increase of 2.65 percent for seven years during which the experimental orchard was observed. In the second check orchard for eight years the annual increase averaged 6.67 percent. This was about what would be ex- pected in an orchard where no attempt was made to cut out the cankered limbs or excise the cankers. In two large commercial orchards in other parts of the state where an attempt had been made by the owners to cut out all cankered limbs but where rigid excision of cankers had not been practiced, surveys made in 1917 and 1918 showed 35 to 38 percent of the trees SOLia .:-,:-, mws woe of the mm* act as the - ^ . . . ,.. - UHC C3W&VH1 tcXSCUSDuU Off f fee or fa* JWMS m tte fife of M anfcud afc the UK of ::.: ::r M'T ..i::: _r." :." : --: _ . ... _- - . - __ _' . _ .1:7^ : : 11 r Kb 11 i.--: :: \:^ ----- :iiz n>T Ow off UK two trees treated in 1921 am ffte oppoatte adr of -,- _ ~ ___.. - 1 - 1.1 1 I J " : .__'-'' .' ., *" v T*T'.. . -" _ * I *1 T - *T J _ ' ' _ ...'I ... T ' "^ _ _- _ _ __ _ _^. . _ . _1 _ I 1:- IT'" K.'i.. ~ ^ - ~ - . -* ' '* * . _ .'" ' . T . -. . , , , . . . _ , ,..-.,. _ - ___.,__.. .. _.... _ . . . .,.,.. . _,.,_ , ,,-_..__ _. . -.._ ... HJH^SVf ^H2B^^DK3BMBMU BHK.~ HV^IR Jw UB^BClBE9il. SB^^DO^POE^Bt m^BS mfKmj ^BflS 0KOC ","- !_>'' '" r'*^ "I -1 .'. -''"-.' " '1 1 " i -" /ZI 1 ' .-: 1" ." ; " : i ..*'."" i loan IB IffiwK onhads :: ^- " -- iJi-: l-u:.- ----. .- -,- . 0f wvod boBft lauviy if ever : : ,'/; ; Ama. BLISTER. CUTEK EOTHoacns .- OL Bdost infections in. ti. broken limbs, especially in the tops of the trees. 7. Cankers about wounds do not riiHMiiiy indicate flat the wound was the original seat of iniection- & Cankers ordinarily appear htii the lilinlj dry jjifcam is cloae to Hie gnrfacr of the fimb. 9. Wood atwaaiua is extensive before the irflrr'T appeal on tte snrface. 10. Physical faefton, soch as types of aofl, ate of oMAaid, and amount of rainfall. : canker. 11. Drainage seems to hare some eanker in that poorly drained areas eased trees than those wefl diaiafd 12. Type of tree growth: is am important factor in that- trees having a uniform growth thruout their derelopnenk are IBB Eoxlr to de- velop cankers than tiiose rmkrrg a rapbi ZTIJ-^-JI i" <:OT cerl.;ii :>L- lowed by restricted growth, at another. 13. pitting oS diseased Iimbe r practiced by many lailnuliulm,, does not eliminate the rfii**B. from the tree. 14. Excision of raaini is caTtLliii. is redocmg the anaaber of newly infected trees if ^nnTBal exoaons are made aad if no eaafeers are overlooked. 15. Proper attention, to prnning and eare of woraids in the eariy lif e of the orchard will assure the owner of an onhaid trees that are free from this disease, 16. The only satisfactory method of control in infected ondbanfe is careful and consistent p-Irm : ~ . : RECOMMENDATIONS FOR COMTXOL Details concerning control of bonier canker are gjhren in Orcolar f this Station. Following is a brief aaaaaaiy of these r some modifications made necessary by more recent 1. Varieties susceptible to blister canker, such as Ben Davis and Gano. should be avoided. 2. If Ben Dave is planted, hignlhr iiiiinliai taiietie^, sack as Grimes, York Imperial, Ofckaliuft, or Winesap, ^knwld be planted the adjacent rows rather than moderately uu\M,piMi TarietK&. as Delicious. Yellow Transpcire-nfe^ or Jonathan. Lit growing varieties with *1wBnjf* l^ptft of gnmth are leas naneptible than rapid-growing varieties with: n^g^*- gpuatb 3. If new orchards of susceptible varieties are pkwte4 ttey afe - should not be planted near older orchards la which is prevalent. 90 BULLETIN No. 340 4. Young trees should be pruned and trained early in their de- velopment so as to avoid the need for heavy, pruning later. 5. Susceptible varieties should not be stimulated to make exces- sive growth at any one period in their development. Soil treatments should be regulated so as to secure an even growth during the life of the orchard. 6. Good drainage should be assured before the orchard is planted, but if the orchard is already established, care should be taken to se- cure adequate underground drainage in all parts of the orchard. 7. Frequent inspections of the trees should be made and all sus- picious cankers carefully examined. If they are blister cankers, efforts should be made to cut out the limbs on which they occur, or the trees, if young, should be destroyed and replaced. 8. When the trees begin bearing, the branches broken by an over- load of fruit or by the carelessness of pickers should receive special attention during pruning operations the following winter. The pruners should be instructed as to the proper method of treating such wounds, as given in the preceding discussion of the subject. 9. If the disease has been established in an orchard, the annual excision of cankers as outlined in this bulletin and in Circular 258 of this Station should be followed. Success depends upon complete elimination of spore-bearing surfaces. A few cankers overlooked during a season may result in numerous new infections. UNIVERSITY OF ILLINOIS-URBANA