Evaluation of fungicide programs for control of watermelon downy mildew, 2007

摘要

The experiment was conducted at the Oklahoma State University Entomology/Plant Pathology Research Farm in a field of Norge loam previously cropped to winter peas. Granular fertilizer (56-86-86 lb/A N-P-K) and lime (1.2 ton/A) were incorporated prior to direct seeding on 16 Jul at a rate of 3 seeds per ft. The herbicides Dual Magnum II at 1 pt/A and Sandea 75DF at 0.75 oz/A were broadcast after planting to control weeds. Plots were top-dressed with additional granular fertilizer (37-0-0 lb/A N-P-K) on15 Aug. Plots were single rows, 25 ft long and spaced 15 ft apart. Plots were thinned to a 2-ft within row spacing. Squash bugs were controlled with Ambush 2E at 12.8 oz/A on 14 Sep. The original objective of the trial was to evaluate fungicide programsfor control of gummy stem blight caused by Didymella bryonae. Plots were inoculated by sprinkling oat kernels colonized by D. bryonae along the center of each plot on 17 Aug. Treatments were arranged in a randomized complete block design with four replications. Fungicides were applied using a CO2-pressurized wheelbarrow sprayer equipped with flat-fan nozzles (8002VK) spaced 18 inches apart. The sprayer was calibrated to deliver 24 gal/A at 40 psi. Fungicides were applied six times on 7-day intervals beginning at flowering on 17 Aug. Rainfall during the cropping period (16 July to 2 Oct) totaled 1.2 inches for July, 1.31 inches for Aug., and 4.6 inches for Sept. Plots received sprinkler irrigations at 0.5 inches per application to promote plant growthand disease development on 29 Jul, 3 Aug, 7 Aug, 10 Aug, 14 Aug, 1 Sep, and 24 Sep. Disease incidence was periodically assessed by visually estimating the percentage of leaves with symptoms (including defoliation) and defoliation alone in three areas ofeach plot. Yield of marketable melons weighing at least 14 lb was taken on 2 Oct.