Evaluation of fungicides for gray leaf spot control in field corn in Ohio, 2007.

摘要

The trial was conducted at the Ohio Agricultural Research and Development Center near Wooster. The soil type was a Ravenna silt loam. Seeds of Pioneer Brand Hybrid 33J56, susceptible to gray leaf spot, were planted on 24 Apr. Each plotconsisted of four 30 ft long rows spaced 30-in. apart. The experimental design was a randomized complete block design, with four replicate blocks. Standard herbicides (2-4 D, Roundup) were used to control weeds, and fertilizer was applied based on asoil test (400 lb/A 19-19-19 and 200 lb/A Urea). Fungicide treatments were applied with a high-clearance sprayer fitted with 8 nozzles adjusted to deliver approximately 20 gal/A at 40 psi. A single application was made, either at V10 (approximately10-13 days before tasseling, (3 Jul) or at R1 (16 Jul). Plots were inspected for disease (gray leaf spot) development during the months of Aug and Sep (between late dough and early dent plant growth stages). Six plants were arbitrarily selected from thetwo center rows of each plot and the percentage of leaf area covered (severity) with lesions of GLS was estimated on the ear leaf and the first (ear -1) and second (ear - 2) leaves below the ear leaf. Rainfall for the months of Jul, Aug, and Sep was 6.46,1.26, and 2.86-in, respectively. Total rainfall for the period between 9 Jul and 23 Jul (V10 to one week after R1) was 2.82-in. Minimum, average, and maximum temperatures for Jul, Aug, and Sep were 47, 70, and 91; 50, 73, and 92; and 35, 65 and 92 F, respectively. Due to the warm, dry conditions, disease levels were very low in all plots. Average gray leaf spot severity was less than 1% in the untreated check plots, and even lower in the fungicide-treated plots.