Evaluation of several fungicides, alone and in tank-mixtures with the phosphonic fungicide Rampart, for control of lettuce downy mildew, Winter 2007.

摘要

An unspecified variety of ‘Chinese leaf lettuce’ susceptible to downy mildew was planted in a 0.4-A commercial field 25 miles south of Clewiston, FL on 3 Dec 2007. The soil, classified as Immokalee fine sand with a soil pH of 7.4, was fertilized according to soil test recommendations. Lettuce was direct-seeded in fourrows with a 10-in. row spacing on top of 8-in. raised beds formed on 6-ft centers. Plants were densely planted for leaf production and final plant spacing within the row was approximately 1-in. The experiment consisted of a randomized complete block design with three replications of ten treatments. Experimental units were 4-row 6-ft bed sections, separated on the end by 5-ft alleys. Chemical treatments were applied using a CO2 backpack sprayer. Two passes were made over each experimental unit, with thehand-held boom spraying two lettuce rows per pass. The boom was equipped with three Tee-Jet 11003 flat-fan nozzles. Foliar sprays were applied at 30 psi, delivering a final spray volume of 62 gal/A. Fungicide treatments were applied on 28 Dec 2007, and on 4 and 10 Jan 2008. The nonionic s urfactant, Induce, was added to all fungicide mixtures at a rate of 0.125% v/v. Diseasepressure arose from natural inoculum and downy mildew lesions were first observed in the trial area on 2 Jan. Downy mildew incidence and severity were assessed on 10 and 18 Jan 2008. Percent disease incidence was measured by examining ten randomly selected lower leaves for the presence of visible downy mildew infection.Disease severity was calculated by visually estimating the percent leaf area exhibiting downy mildew symptoms on the ten randomly selected leaflets. Disease control was visually rated on a 0-10 scale with 0 representing no control and 10 representing total control. Ratings were performed relative to the untreated control on 22 Jan 2008.