J m* V . S. I DEPARTMENT ( >F AGRICULTURE, Bl T RKAU OF PL \.\T INDUSTRY Circular N T o. 23. B. T. GAIXOWAY, Chief i. POTATO DISEASES IN SAN JOAQUIN COUNTY, CALIFORNIA. W. A. OKTON, Pathologisi i\ Charge oi Cotton vnd Truck Diseases \m> Plant Dise \>i: %\ k\ i 5 . rON : GOVERNMENT PKiMTINQ OFFICE : 1909 D#CUm£nT F J- hfpT OEPOSITORY BUREAU 01 PLANT INDUSTRY. Physiologist and Pathol Bureau, Beverlj T Galloway. Physiotogm mid Pathologist, mid Vssistani Chief Albert P. Woods. Laboratory of Plant Pathology, Erwin I-'. Smith, Pathologist in Charge. Fruit Disease In n . Merton 1'.. Waite, Pathologist in Charge. Laboratory 0/ Forest Pathology, Haven Metcalf, Pathologist in Charge. ■1, at Truck Diseases and Plant Diseasi Survey, William a, Orton, Patholo; Charge. • Pathological Collections anil Inspection II 01 I. . Flora \V. Patterson, Mycologist iu Charge. Plant Lift History Investigations, Walter T. Swingle, Physiologist in Chat Cation Breeding Investigations, Archibald D. Shame) and Daniel N. Shoemaker, physi- ologists in Charg investigations, Archibald D. Shamel, Wightman W. Garner, and Ernest II Mathewson, in Charge. Col l7ivcstigations, Charles P. Hartley, Physiologist in Charge. .ml Drought Resistant Plant Breeding Investigations, Thomas II. Kearney, Physi- ologist in Charge. Soil Bacteriology and Water Purification Investigations, Karl F. Kellerman, Physlolo in Charge. Bionomic Investigations of Tropical and Subtropical Plants, Orator F. Cook, Bionomist in Charge Drug and Poisonous Plant and Tea Culturi •lions. Rodney II. True, Physiologist in Charge. Physical Laboratory, Lyman .1. Briggs, Physicist in Charge. Agricultural Technology, Nathan A, Cobb, Crop Technologist in Charge Taxonomic and Rangi Investigations, Frederick V. Coville, Botanist iii Charge. Farm Management, William J. Spillman, Agriculturist in Charge. Grain Investigations, Mark Alfred Carleton, Cerealist in Charge. Arlington Experimental Farm und Horticultural Investigatioi . I ■ C. Corbett, ll.irti- culturist in Charge VegetabU Testing Gardens, William W. Tracy, sr., Superintendent. Sugar-Beet Investigations, Charles Townsend, I'athologisl in Charge. H'i tern \in ii nil in a/ Extension, Carl S. Scofield, Agriculturist in Charge Dry-Land Vgriculturi Investigations, E. Channing chile. 11. Agriculturist in Charge. Pomological Collections, Gustavus B. Brackett, Pomologist in Charge. Field Investigations in Pomology, William A. Taylor and G. Harold Powell, P ogists in Charge. Experimental Gardens and Grounds, Edward M. Byrnes, Superintendent. Foreign Seed and Plant Introduction, David Fairchild, Agricultural Explorer in Charge. fun,, 1, cop Investigations, Charles V. Piper, Agrostologist in Charge Seed Laboratory, Edgar Brown, Botanist in Charge Grain Standardisation, John 1 >. Shanahan, 1 cop fochnologist in Chargi Subtropical Garden, Miami, Fla., P. .1. Wester, in Charge. Plant Introduction Garden, Chico, Vol., W. W. Tracy, ir Assistant Botanist in Charge. South Texa Garden Brownsville, Tex., Edward C. Green, Pomologist In Charge. Cooperative Demonstration Work, Seaman A. Knapp, Special Agent in Charge Seed Disti iimti o, 1 (Directed i; 1 hiel of Bureau), Lisle Morrison, Assistant in General Charge. Editor. .1. E. Rockwell. Chit 1 Clerk, James E. Jones. [Cir.23] B. P. I i"" POTATO DISEASES IN SAN fOAOUIN COUNTY, CALIFORNIA. INTRODUCTION. During recent years an important center for vegetable growing has developed in San Joaquin County. Cal.. through the reclama- tion of the lulc ni- peat hind- in the deltas of the San Joaquin and Sacramento rivers. The potato is the principal crop, about 25,000 ai r. - being planted. It is also one "I' the most profitable crops under normal conditions. The agriculture of the region is remarkable for tin' large areas under one management, reaching several thousand acre- in some cases. Most id' the land is cultivated by renters who arc not perma- nent residents. The tide land- lie for the most part near of below the high-tide level of the river. They were originally partially over flowed and covered with a dense growth of marsh plant-, but arc now reclaimed by the construction of levee? along the river bank and the installation of pumping plants to remove the water. The soil consists of a deposit of several feet of the peal formation locally known as tide, which contain- a large amount of organic matter only partially decomposed, formed by the decay of rushes, sedges, and other plant- native to those warm valley mar-he-. Under cultiva- tion and irrigation this soil work- down to a ven fine and uniform texture. I>nt i- at first quite rough and lumpy. Since the rainfall is only about lo inches, irrigation i- essential for crop production on these peat soils. Water for this purpose i- ad- mitted from the river and distributed over the level fields in small ditches BO to V(| feel apart. The water passes quickly through the loose peat soil until the water table i- raised nearly to the surface, making in effect a system of subirrigation. A- the land lies too low for water to run off, a system of drainage is essential. This i- ac- complished by mean- of large pumps which discharge the water into t he ri\ it. Potatoes are planted in March and April as a rule, and are har- vested as the market requires them, from the la-t of September through October and Xovember. While several other crops are grown on the peat land-, including barley, beans, onion-, and asparagus, no 4 POTATO DISEASES IX CALIFORNIA. fixed system of rotation of crops is practiced. It is customary to plant potatoes when the lands are first cleared, and usually for two or three years, after which the diminished yield and inferior quality of the potato crop cause the land to be put into barley or beans. A fter an interval of one or more year- potatoes are again planted, since, as this crop returns the largest profits, the growers desire to plant it a- continuously as possible. This, id' course, is not good agricull ural pract ice. It Inn: been found impossible to grow potatoes continuously on these peat lands in spite of their apparently inexhaustible fertility. The first crops grown after the land i- reclaimed are phenomenally large, •'Win to 800 bushel- per acre, and of good appearance. After the first or second year, however, the yield diminishes rapidly and the tubers become rough and scabby to such an extent a- to wipe out all profits. In the summer of 1908 the Bureau of Plant Endustry was called on to determine the causes of this condition. An inspection of the fields brought out the fact that several plant disease- appear to con- stitute the principal limiting factor- in this industry. A diagnosis of the troubles, with some suggestions for their treatment, i- given herewith. Entirely adequate measures for their control are not yet a\ ailable, but may perhaps be worked out by further experimentation. POTATO WILT. THE iaisi: or " POTATO-SICK " LANDS. Idie principal cause of the marked decrease in the yield of old potato land is the presence of a fungous disease, the wilt, or dry-rot (Fusarium oxysporum Schlecht.). The connection of such a parasite with the troubles experienced had not been realized by the growers, nor had the fungus been reported from the Pacific coast, but a careful study of it had been made in the east by Dr. Erwin F. Smith and Mi-. Deane B. Swingle," of this Bureau, who worked out quite fully the nature and cause of the disease and the character and life history of the fungus causing if. The wilt is apparently not as prevalent or a- injurious in the Eastern State- ;,- on the Pacific coast, and but little work has yet been done on methods for controlling it. DESCRIPTION 01 I ill: WILT. The effects of the wilt a- observed in California are exactly as described by Smith ami Swingle from plant- grown in the District of Columbia. The disease first becomes noticeable when the plant- are about a foot high, though in mild cases it may not appear nil "Bui. 55, Bureau of Planl Industry, "The Drj Ro1 oJ Potatoes Due to Fusarluiu Oxysporum." 1904. I r. 23] POTA L'O DISK \sl S l.\ CALIFORNIA. f> near maturity. The leaves have a lighter green color and slowly assume a dull, unhealthy appearance, with a rolling or curling of the argins. The progress of the disease is slow. Gradually the tops n lll "' r '"' fall over and the general etl'ecl is of |)reniature ripening. diseased plants are easily pulled up; the roots are partly dead and brittle. The will fungus frequently appears on them as a white or pink mold, and when the underground portion of the stem is cut aero - a pron iced hrov n discoloration is visible. This brown stain is also found in the branches leading to the tubers, and a thin slice across ''"' -!'' 111 end of the tuber will often reveal its presence there as well. Examination of thin sections of these browned stems under the microscope shows the fungus to be abundant in the water-carrying vessels of both underground stems and roots; where ii appear- a- delicate, colorless threads, bearing tiny elliptical spores. The yield from diseased hills is greatly diminished, particularly if the attack begins early in the season. I in urn ROT or THE 11 B] I."-. When the potatoes are dug there is rarely any external evidence of ,Ih ' disease on them. The major portion of the crop produced from lilted plant- is nevertheless infected, the fungus having entered the tubers through their -terns. If these potatoes are stored in a cold place, but little change occur-, as the fungus requires warmth for its development. When infected potatoes are kept in a heated room or outdoors in a warm climate, a dry-rot soon develops. _ As tne fungus spreads through the potato the tuber shrivels, be- ginning at the stem end; the inside becomes brown and light in weight. Occasionally bacteria cause a. secondary soft-rot, which pro- m> ds more rapidly. An earh form of (hi- Fiisarium DISEASES IN CALIFORNIA. '.I '■■'1 in wet soils. It is the experience of growers that n varies greatly in different seasons, yet, nevertheless, it can be pre- vented b\ excluding the germs of the disease. l*RE\ l\ I'M i: MEAS1 RES I in; SCAB. U) Clean seed. The most frequent source of infect ion lies in the seed planted, and the experience of eastern growers has Keen that bv disinfecting the seed and by planting in land free from scab a dean "•op may be produced, it is therefore of the greatest importance* thai those California growers who have land not already infected b\ this disease should seek to keep it healthy by allowing nothing but disinfected seed to be planted. I" the majority of cases, however, it is necessary to deal with land iIk " h » s already been infected h\ the cultivation of one or more potato crops. The disease has already been introduced: the problem lm " u> control it. It goes without saying that additional rein- 11,111 should be avoided by disinfecting all the seed planted, in accordance with directions given later in this publication. Additional means to be adopted comprise : (2) Rotation of crops. Scab tends to diminish when land is planted in crops which do not harbor the parasite. Other root crops, however, such as sugar beets, turnips, etc., must be avoided. The 'ength of time required to i'rrr land from scab varies in different sections, but, as a ride, a period of three years will very greatly reduce the amount of disease, though it may not be entirely exterminated a Iter five, or even ten, vears. The principal point to be kepi in mind in choosing rotation crops is "' increase the amounl of organic acids in the soil by plowing under green crops, such as rye, clover, vetch, etc., which by their decay tend to produce an acid reaction in the soil. It is possible that ,lu ' soil can be further favorably modified by the use of fertilizers. RUch ; '^ acid phosphate, muriate of potash, land plaster, etc.. which leave an acid residue. It seems at first thought illogical to advise plowing under ere,.,, crop, on soils largely made up of organic mat ter and to suggest fertilizers where there appear- to be no lack of plant food. No Mid, positive recommendation is intended, but in the absence of knowledge of the subject such experiments to tesl this should be undertaken. The beneficial effect of such treatment is well recognized in the Eastern States. (3) Soil treatment. The chemical treatment of the soil to reduce promises but little. Applications of sulphur at the rale of 3i pounds per acre have been used with some degree of success in Del ware and New Jersey and might give good results in California. [Cir. 23] 10 POTATO DISEASES IX CALIFORNIA. SEED TREATMENT FOE m All." The most effective method of disinfecting seed potatoes is by the use of formaldehyde gas liberated by mixing the commercial solution with potassium permanganate. This method is adapted to the disinfection of large quantities of potatoes in a short time. To use it. an air-tight shed should he constructed of sufficient size to hold whatever quantity it may lie desired to treat at one lime. This may he made of rough lumber, lined with building paper and provided with a tight door. The potatoes may lie treated in sacks, hut these sacks must be piled so as to allow a free circulation of air all around them. It is suggested that they he piled in tiers, with two 2 by 4 inch scantlings between each layer of sacks. Space should be left in the center of the building for placing the charge of formalde- hyde, which should he set oil' in shallow pans, such as galvanized washtubs. For each 1,000 cubic feet •_;:; ounces of potassium per- manganate and ."J pints of formaldehyde should he allowed. After the potatoes are properly slacked and everything is made ready, the permanganate should lie spread in a thin layer on the bottom of the pan. the required quantity of formaldehyde poured in and stirred quickly, and the building vacated. The building should then he kept closed tight for twenty-four hours, when it may be opened and the potatoes taken out. Formaldehyde i- a nonpoisonous hut highly irritant fluid which can be purchased in -mall lots at about 50 cents a pound, in carboy lots at 20 cents, or in barrel lots at about 12 cent-. Potassium per- manganate is a reddish brown, crystalline substance, purchasable at from 13 to 25 cent- a pound. The precaution should be taken not to pile any potatoes directly over the pans or within 3 feet laterally, as the gas there mighl he strong enough to injure the potatoes and destroy their germinating power. The formaldehyde works best in a humid atmosphere. It i- therefore advised that the floor of the shed !»• wet down before the treatment i- made. The potatoes, however, should not he wet. i- the disinfection is more thorough if the surfaces are dry. Small quantities of potatoes may he disinfected by soaking in a solution of 1 pint id' formaldehyde to .",(> gallons of water for two hours. Either the gas or the solution treatment may he applied some time previous to planting, provided the potatoes are not exposed to reinfection by being put into receptacle- that have previously held scabby potatoes. The treatment should also he made befor< the potatoes arc cut for -eed. "Adapted from Bulletins lit and tin. Maine Agricultural Experinienl sta- tion, by \V. .1. Morse. 23] 1M . I aim DISI \.-> S IX CALIFOBK IA. II i dm ui SKKD i 1:1 v I \i I \ I . I i. expense connected with the treatmenl of seed potatoes b\ the gas method will vary in different cases according to the amount of labor required in handling and whether a special building has to be erected for the purpose. The cost of labor and of the building will be the principal items. The cost of the materials need not amount in over 1 cent pei sack. For example, a shed \-2 by _l feet and 7 feet high contains 2,01G cubic feet and would require '■) pounds of potassium permanganate, costing GO cents, and C> pints of formalde- hyde, costing $1.20; total. $1.80. Two hundred sacks can easily be treated at once in such a shed. An entire day should be allowed for each treatment. DECAY OF POTATOES. Considerable loss is occasionallj experienced from the rapid decay of potatoes short h after harvesting. It is reported that an entire shipment of potatoes will sometimes '* go down" in a few day- or while en route to market. This trouble is locally known by the issive term " leak." or " melters." The affected potatoes turn a dull brown outside; the flesh i- buff or brown and very soft. When subjected to pressure a copious amount of clear brown liquid is discharged. There is no bad odor in the early stages. CAT SE oi I HE "" l.liAK." This form of decay is due to the invasion of a fungus. RJtizopus cans. This fungus can enter only through wounds, and experi- ments in the laboratory have corroborated the testimony of the grow- er- that potatoes injured by careless digging especially are attacked. The fungus spreads rapidly under favorable conditions, growing between the cell walls. Later the cells are separated, and hence the rapid softening of the tissue. The fungus i- propagated by -pore- produced in large heads or sporangia. It can grow on a great variety of dead organic substances. AYhile it is not usually considered a dangerous parasite, it is known to cause decay in sweet potatoes, apples, and pear-, and a related fungus causes a disease of lily bulbs. Ill \| EDIA] M I \-l RES I ' IK THE " LEAK.*' for the control of this disease may be based on our know ledge of it- cause : Avoid breaking the skin of the potato in handling. Nature has given the potato an effective protection against such fungi in an unbroken epidermis. Rhizopus is a wound parasite, and fork holes and bruises are it- principal mean- of entrance. 23] g - - - - - - - . - Fungus. ] - - _ - that inf eei _ - - . i BOTftTl ■ - - o - - - _ _ _ - - - - - : - - - - : _ " - _ _ - - _ . _ • I i g the f - ' - _ - to diseases ■ h • - _ - • - - -- l tatoe- ' - - - _ - _ E - A- _ - - 2T» - - - - - - - -- - I - " - _ - _ - - - *1 II - _ same g - - - - ------ - - _ : _• Th< _ _ - 14 POTATO DISEASES IN CALIFORNIA. \1.I ALFA. Experimental plantings of alfalfa made at Middle River have suc- ceeded well. In the light of these experiments ii seems probable that alfalfa will do well on the peat lands where the water is not allowed to come too near the surface. The use of alfalfa, however, would probably necessitate leaving the land in this crop for several years, which might be desirable where the land had become badly infested with potato diseases. Among the varieties tested at Middle River the Arabian variety was decidedly better than any other. On November 11. 1908, a few weeks after the last cutting of all of the plots, the Arabian alfalfa was 12 inches high, while the ordinary alfalfa had made scarcely any growth. This ability of the Arabian alfalfa to grow during the cool weather of late fall and early spring would be particularly valuable from the standpoint of winter pasturage. OTHER FOB Ml I ROPS. Doubtless many other forage crops, both legumes and grasses, would succeed on the peat lands. Experimental plantings of a large number will be made. The list of those that are known to be suc- cessful on these lands is sufficient, however, to meet present needs, and the knowledge of each is so definite that no farmer need hesitate to plant those recommended in these pages. Approved : James Wilson. St cretary of . I grieidturt . Washington, D. ('.. January .'', 1909. [Cir. 28] o UNIVERSITY OF FLORIDA 3 1262 08928 9663 t