Downy Mildew Control New Chemicals Greatly Reduce Damage from Downy Mildews of Leafy Garden Vegetables

Downy Mildew Control new chemicals greatly reduce damage from downy mildews of leafy garden vegetables

C. E. Yarwood

Zineb spray is the best fungicide yet was divided into treatment plots four feet Of the three dusts tested, a mixture of tried for the control of the downy mildews long with a two-foot row of buffer plants 5% spergon-tetrachloroquinone-and of spinach, beets, lettuce, and hops. between each treatment. 95% dusting sulfur was the best. Sulfur Zineb is the compound zinc ethylene Plants in the buffer areas were inocu- alone gave significant control. bisdithiocarbamate. lated by spraying them with downy mil- In the 1949 test at Milpitas, 10 plots Studies have been underway on spin- dew sporangia collected in another field. of spinach 16 feet long were marked out. ach downy mildew for 15 years. No On March 3d, and weekly thereafter Five alternate plots were treated April method of fungicidal control of the dis- until April Sth, duplicate randomized lst, 7th, and 14th with 0.2% zineb plus ease was known in 1939. plots were sprayed or dusted with a va- spreader. There was a slight but un- The studies were made because downy riety of fungicides. Seven randomized counted amount of mildew in the field mildew occurs each year in places where plots were left untreated. On April 11th when the test was started. spinach is grown. It is also frequent on incidence of disease and yield of plants On April 21st, the mildew lesions on beets and lettuce. Sometimes it causes were recorded. seven random leaves per plot averaged great loss to these crops in California. 11 for the untreated areas. None was Downy mildew appears as pale spots found on treated areas. on the upper side of leaves and as fuzzy, Spinach Test Results gray-looking spots on the lower side. It All fungicides tested reduced signifi- occurs chiefly on the older but still vigor- cantly the amount of disease as compared Tests on Beets and lettuce ous leaves and slowly kills them. with the untreated plots. The same treatments with sprays and In 1946, greenhouse trials showed that Sprays used included 0.1% phygon dusts were used in 1947 for the control several spray and dust fungicides control with spreader, 0.2% zineb with spreader, of beet downy mildew and lettuce downy downy mildew under conditions of heavy and 0.2% bismuth subsalicylate with mildew. inoculation. Sulfur dust was apparently spreader. Also tried were 0.3% bordeaux On the highly susceptible beet variety, more effective than copperlime dust.. with spreader, 0.3% bordeaux with 0.3% Asgrow Canner, downy mildew was more cottonseed oil, 0.57, resin soap with 0.5% severe and fungicidal control was less lime sulfur, and 1% lime sulfur with successful than with spinach mildew. On Trial Conditions at Milpitas 0.1% zinc sulfate. the untreated plots, 84% of the plants Four trials under natural conditions The dusts used were sulfur, 5% sper- became systemically infected. were undertaken at Milpitas in 194749. gon with 95% sulfur, and 6% zerlate Zineb spray reduced systemic infec- In two trials the incidence of disease was with 94% inert material. tions to 29%, while spergon-sulfur dust too low to yield dependable results. Zineb was the most effective spray. reduced them to 61%. Only these two In the 1947 plot, two varieties-Blooms- Bismuth subsalicylate was the spray next treatments gave good control. dale and Viroflay-were seeded in raised most effective. This compound must be On Imperial No. 615 lettuce the con- double rows on January 24th. The area finely divided for best results. Continued on page 16

WACNUTS the information obtained is given in the resistance is at a high level, but when it is accompanying table. It should be noted low, timely and thorough applications Continued from page 7 that approximately 50% of the eggs laid are necessary for successful control. tors becomes more apparent with an in- were parasitized. Because of the powerful natural en- crease in population. This is particularly Although the amount of parasitism was vironmental factors that tend to regulate true in regards to predators and para- insufficient to successfully control the codling moth population efforts should sites, which often occur in large numbers codling moth, the data show that the large be made to avoid practices that might when their host becomes very abundant. codling moth population created condi- shift them to favor the codling moth. To some extent this happened with the tions favorable for a rapid rise in a para- Control measures should be used with codling moth during the 1949 season. site population. discrimination,applied only when needed, There was a very large second brood of The conflict between the codling moth and the insecticide used at a rate no codling moths, and in the experimental and its natural controlling factors is al- higher than necessary to insure satisfac- orchard at Linden there was a heavy dep- ways present, but the value derived is torv control. osition of eggs. The average number of seldom clearly seen. A more thorough A. E. Michelbacher is Assistant Professor of eggs per nut was something more than knowledge concerning the relations that Entomology and Associate Entomologist in the 1.75, which was considerably higher than exist between the two is certainly deserv- Experiment Station, Berkeley. usually encountered. The eggs were heav- ing of intensive investigations. W. W.Middlekauff is Assistant Professor of ily parasitized by Trichogramma embryo- Environmental resistance appears to Entomology and Assistant Entomologist in t.+e Experiment Station, Berkeley. phagum Hartig. Parasitized eggs usually play an important role in the success of Donald Davis is Research Assistant in En- contained three parasites. a codling moth spray control program on tomology in the Experiment Station, Berkeley. A number of surveys were made to walnuts. Apparently satisfactory control The authors are staff members of the Univer- determine the degree of parasitism and is easily obtained when environmental sity of California College of Agriculture.

10 CALIFORNIA, AGRICULTURE, JULY, 1950 DONATIONS FOR AGRICULTURAL RESEARCH Gifts to the University of California for research by the College of Agriculture accepted in May, 1950

BERKELEY -now ready for distribution- American Cyanamid Company...... 24 pounds aerocyanate weed killer Single copies of these publications or a cata- Agricultural Extension Service logue of Agricultural Publications may be oh- E. S. Browning Company...... 6 pounds larvicide tained without charge from the local office of Division of Plant Pathology the Farm Advisor or by addressing a request to: Dr.WilliamH.Boynton ...... $134.51 Publications Office, 22 Giannini Hall, Uni- Division of Veterinary Science versity of California, College of Agriculture, California Spray Chemical Company...... 10 pounds Lindane Berkeley 4, California. Agricultural Extension Service Contra Costa Vegetable Oil Corporation...... ,100 pounds almond meal GUM DISEASES OF CITRUS IN CALI- Division of Poultry Husbandry FORNIA, by L. .I.Klotz. Exp. Sta. Cir. Dow Chemical Company...... Dowfume W-40, Dowfume N, Dichloro Butene 396, June 1950. Contains the latest avail- 15 Ibs. DN dry mix 1 gal Amine salt of 2 4-D 1 gal. DN-289, able injormation on the cause, prevention !h gal. Gen. Weed Killer,’ 2 Ibs. 50% wettable IPC, 20 lbs. Dow STCA and treatment of gum diseases on citrus Agricultural Extension Service trees in California. Julius Hyman & Co...... 25 pounds of Dieldrin Compound 497 Division of Entomology & Parasitology Lederle Laboratories Division American Cyanamid Company. .20 Ibs. Aureomycin primary cake 2.5 % MILDEW Division of Poultry Husbandry Mr. George E. Lodi...... ZOO pounds Urea type Nitrogen Fertilizer Continued from page 10 Agricultural Extension Service Monsanto Chemical Company...... 2 pounds 100% 2,4-D, 2 pounds Santo Merse wetting agent trols averaged 49 downy mildew lesions Agricultural Extension Service on eight heads per plot. Zineb spray with Naugatuck Chemical Company...... 10 pounds Beta-Chloroethyl-Beta-Alpha-Methyl,Ethyl Sulfite three lesions, spergon-sulfur dust with Agricultural Extension Service three lesions, and sulfur dust with 15 Rohm & Haas Company...... ds Dinitro Capryl Phenyl Crotanate lesions per eight heads, gave clearly significant control. Rohm& Haascompany ...... $1,000.00 Division of Food Technology Shell Oil Company...... 20 gallons Shell Oil Weed Killer No. 10 Tests on Hops Agricultural Extension Service The trials with hop downy mildew were Shell Oil Company...... 5 gallons 0.5, 840 (Chlorobromopropene) Division of Plant Pathology independent of the other tests. Stauffer Chemical Company...... 20 gallons carbon bisulfide Field results under epidemic condi- Division of Plant Pat tions for hop downy mildew were difficult Strawberry Institute of California. .... 00 strawberry plants, variety Lassen to obtain. The disease was severe in only Div two of the 15 years of the studies. Thompson Horticultural Chemicals Corporanon...... l pint 2,4-D In one test, 0.8% tribasic copper sul- Agricultural Extens fate, 0.6% spergon, and 0.2% zineb were Yoder Brothers ...... : ... 300 Albatross chrysanthemums 600 Indianapolis pink fhqsanthemums applied May 25th and 30th; and June Division of Plant Pathology 4th, 9th, and 14th, 1948 to adjacent single rows of hops 26 hills long. DAVIS On June 14th the untreated vines California Fertilizer Association...... 512,000.00 Division of Truck showed 63% of the trained terminal Crops Donsing Breeding Farms...... ,100 White Leghorn Chickens shoots with systemic infection, 52% of Division of Poultry Husbandry the untrained basal shoots with systemic Lederle Laboratories Division American Cyanamid Company. .50 grams Aureomycin Hydrochloride infection and an average of 312 downy Division of Animal Husbandry mildew lesions per leaf on the lower Lederle Laboratories Division American Cyanamid Company 10 pounds Animal Protein Factor Supplement, Lot 30 leaves. Division of Poultry Husbandry The row treated with tribasic copper Merck & Co., Inc...... 6 pounds experimental animal protein factor supplemental sulfate showed 4% of trained and 4% of Division of Poultry Husbandry the basal shoots with systemic infection Naugatuck Chemical Company...... ,220 pounds Aramite and 38 lesions per leaf. The row treated Division of Pomology with spergon showed 7% of the trained Research Corporation ...... and 9% of the basal shoots with systemic Division of Chemistry infection and 21 lesions per leaf. Western Condensing Company...... Zineb again gave the best control. The Division of Dairy Industry zineb-treated row showed 8% of the LOS ANGELES trained and 3% of the basal shoots with American Cyanamid Company...... 200 pounds Aero Cyanamid Granular 3 cases Insecticides systemic infection and two lesions per Division of Ornamental Horticulture leaf. W. Atlee Burpee Company...... $50.00 This result was similar to that on all Division of Ornamental Horitculture the other tests in the studies in that zineb Northrup, King and Company...... 1 bag Highland bent proved itself the most effective fungicide. 3 pounds extra fancy Kentucky bluegrass 1 pound Meadow fescue Division of Ornamental Horticulture C. E. Yarwood is Associate Professor of Plant Pathology and Associate Plant Pathologist in Pacific Toro Company, Inc...... 1 sod lifter the University of California College of Agri- Division of Ornamental Horticulture culture Experiment Station, Berkeley.

16 CALIFORNIA, AGRICULTURE, JULY, 1950