Evaluation of premix foliar fungicides at the R4 growth stage for management of frogeye leaf spot on soybean in Arkansas, 2018

摘要

Foliar fungicides were evaluated as a solo and tank mix for control of strobilurin-resistant frogeye leaf spot. This trial was located at the Newport Extension Station in Newport, AR in a field of Dundee silt loam previously cropped to soybean. The soybean cultivar 'GoSoy 4814' was planted on 8 Jun at a seeding rate of 150,000 seed/A. Weeds were controlled using Liberty (1 qt/A), Roundup (1 qt/A), and Boundary (1 qt/A) applied pre-plant on 6 Jun followed by Roundup (1 qt/A), Prefix (2.3 pt/A), and ENC (1 qt/A) applied post emergence on 2 Jul. Plots consisted of four, 27-ft-long rows spaced 30-in. apart. The experimental design was a randomized complete block design with four replications separated by 3-ft fallow alleys. Plots were inoculated with approximately 4,000 spores/A of several different isolates of strobilurin-insensitive Cercospora sojina on 1 Aug through a mudmaster sprayer and irrigated overhead to promote disease development. Rainfall and Irrigation during the cropping period totaled 26.14 in. with monthly totals as follows: Jun, 2.0 in.; July, 3.8 in.; Aug, 8.2 in.; Sept 7.4 in.; Oct, 4.8 in. Monthly average maximum air temperatures were 92oF Jun, 91oF July, 88T Aug, 84oF Sept, and 72oF Oct. Monthly average minimum air temperatures were 72oF Jun, 72oF July, 69oF Aug, 66oF Sept, and 52oF Oct. Fungicides were broadcast through flat-fan nozzles (Tee-Jet 110015VS) spaced 30 in. apart on the two center rows per plot using an air pressurized multi-boom plot sprayer. The sprayer was calibrated to deliver 15 gal/A at 32 psi. Treatments were applied at R4 growth stage on 14 Aug. Frogeye leaf spot severity was assessed at 0, 7, and 22 days after treatment (DAT) based on percent leaf area affected of the upper 1/3 of the plant canopy. Diseaseseverity ratings were collected using a 0-100 percent scale. Plots were harvested on 4 Dec using a K Gleaner combine equipped with a HarvestMaster Single BDS HiCap Weighing System. Data was subject to ANOVA using Agricultural Research Manager Software (version 9.0) and means were compared using Tukey's honest significant difference test (P = 0.05).