Evaluation of fungicide alternations for control of downy mildew on broccoli, Spring 2009.

摘要

Broccoli of the downy mildew susceptible variety ‘Bluewind’ was planted in a 0.5-A field at the Everglades Research and Education Center in Belle Glade on 5 Feb. The soil, classified as Pahokee Muck with a soil pH of 7.0, was fertilized according tosoil test recommendations. Broccoli was direct-seeded in two rows with a 12-in. row spacing on top of 6-in. raised beds formed on 3-ft centers, and was thinned to stand on 3 March, with a final in-row plant spacing of 9-in. The planting was hand-hoed for weed control and insects were controlled using standard insecticides as needed. The experiment consisted of a randomized complete block design with four replications of ten treatments. Experimental units were 2-row 12-ft bed sections, separated on theend by 5-ft alleys. Chemical treatments were applied using a CO2 backpack sprayer. The hand-held boom was equipped with three Tee-Jet 11002 flat-fan nozzles. Foliar sprays were applied at 30 psi, delivering a final spray volume of 60 gal/A. A nonionic surfactant, Induce, was added to all fungicide treatments at a rate of 0.125% v/v to facilitate foliar wetting and adhesion. Fungicide treatments were applied on 9, and 17 Mar. Disease pressure arose from natural inoculum and downy mildew lesions were observed in the trial area at the time of spray initiation. Disease was assessed by visually examining the entire plant canopy in a 2 sq. ft. section of bed at two randomly selected locations per experimental unit on 18 and 27 Mar. Mildew was rated on a 0-5scale, with 0 = no disease and 5 = downy mildew severe throughout the entire plant canopy. Disease severity was estimated using the Horsfall-Barratt rating scale to assess the percentage of foliage affected by downy mildew at two randomly selected locations per experimental plot. Percentage data were transformed using the arcsine transformation to facilitate analysis.