Cropping sequence and fungicide effects on gray leaf spot and yield of field corn in Ohio, 2007

摘要

Trials were conducted at the Ohio Agricultural Research and Development Center (OARDC). Seeds of Pioneer Brand hybrids 35A34, susceptible to gray leaf spot (GLS), and 34A20, moderately resistant to GLS, were planted on 9 May in Ravenna silt loam at OARDC. Two separate trials were conducted. In the first trial, corn was planted after corn (corn-on-corn), and in the second, corn was planted after soybean (corn-on-soy). The experimental design was a split-plot with replicated blocks (three for the corn-on-corn trials and four for the corn-on-soy trial). Hybrid served as the whole-plot treatment and fungicide application timing as the sub-plot treatment. In the corn-on-corn trial, each experimental unit consisted of four 35 ft long rows spaced 30-in. apart, whereas for the corn-on-soy trial, each plot consisted of four 25 ft long rows spaced 30-in. apart. Standard herbicides 2, 4-D and Roundup were used at label rates, and fertilizers were applied based on a soil test (400 lb/A 19-19-19 and 200 lb/A Urea). Fungicide treatments were applied using a high-clearance sprayer fitted with eight nozzles adjusted to deliver approximately 20 gal/A at 40 psi. Applications were made to separate plots of each hybrid either at tassel emergence (VT, 23 Jul), early silk emergence (R1, 25 Jul) or 50% brown silk (late R1 - early R2, 31 Jul), constituting three fungicide treatments. A fourth plot of each hybrid was left untreated, serving as the check. Plots were inspected for disease (gray leaf spot) development during Aug and Sep (between milk and dent plant growth stages). On 19 Sep, six plants were arbitrarily selected from the two center rows of each plot and the percentage of leaf area covered (severity) with lesions of GLS was estimated on the ear leaf (E) andthe first (ear–1), second (ear–2), and third (ear–3) leaves below the ear leaf. Leaves were also inspected for other foliar diseases. The two center rows of each plot were harvested on 1 Nov, with grain moisture levels ranging from 15 to 18%. Yield is reported as bu/A adjusted to 15.5% moisture.