Best timing of fungicide application for control of narrow brown leaf spot in rice in Texas, 2016

摘要

An experiment was established in a field of League-type clay soil (3% sand, 32% silt, and 64% clay) at the Texas A&M AgriLife Research and Extension Center, Beaumont, TX. The field had been cropped to rice for many years and naturally infested with the narrow brown leaf spot pathogen. Plots consisted of seven 16 foot rows, and spaced 7-in. between rows. This experiment was conducted as a randomized complete block design with four replications. The experiment consisted of eight fungicide timing treatments based on the stage of rice growth: a fungicide application made 1) at 7 days after panicle differentiation (PD + 7), 2) at boot, 3) at heading, 4) at 7 days after heading (Heading + 7), 5) two applications at PD + 7 and heading, 6) two applicationsat boot and heading + 7, 7) three applications at PD + 7, boot and heading + 7, and 8) unsprayed control. Rice was drill seeded at 80 lb/A on 12 Apr. Plots received 50 and 150 lb N/A of urea (46-0-0, N-P-K) on 6 May and 5 Jun, respectively. For weed control, plots were applied with Command (0.3 lb a.i./A) and Permit (0.05 lb a.i./A) on 12 Apr. Irrigation and other agronomic practices followed local recommendations. Narrow brown leaf spot developed from natural inoculum. At the stages of PD + 7 (30 Jun),boot (6 Jul), heading (20 Jul), and heading + 7 (27 Jul), plots were sprayed with PropiMax (propiconazole) at 10 fl oz/A using a CO2 pressurized sprayer equipped with a boom of three TeeJet 8002 nozzles spaced 16-in. apart that delivered at 32 gal/A. On10 Aug, severity of narrow brown leaf spot was rated on a 0 to 9 scale where 0 = no symptoms and 9 = the most severe symptoms (leaves dead). Plots were harvested using a plot combine on 31 Aug. Grain yield and moisture were determined, and rice yield was adjusted to 12% moisture content.