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Evaluation of weather-based foliar fungicide applications for soybean in the mid-Atlantic U.S

Tian Zhou: Virginia Tech

<div>Foliar fungicide applications are a standard practice for some growers, however, fungicides increase soybean yield less than one third of the time in the mid-Atlantic U.S. Yield response to fungicides depends, in part, on the presence of a pathogen and conducive environmental conditions for disease development. The objective of this study was to compare crop developmental stage-based fungicide applications to weather-based applications for foliar disease control and yield response in soybean. On-farm replicated strip trials were conducted at 21 locations from 2014 to 2016. Treatments included no fungicide, fungicide applied at beginning pod (R3), and fungicide applied when environmental conditions favored disease (18-26°C and ≥ 10 hours relative humidity ≥ 95% for 2 consecutive days). Foliar disease was rated bi-weekly and yield was measured at harvest. Frogeye leaf spot and Cercospora leaf blight were the major diseases observed. Environmental parameters triggered fungicide applications at 20 of the 21 locations, but yield response was observed at only 7 locations. Weather-based fungicide applications did not differ in yield compared to R3 applications. However, when environmental parameters conducive for disease occurred within 2 weeks of the R3 stage, R3 applications were more likely to increase yield. Results indicate both crop developmental stage and environmental conditions should be considered prior to applying foliar fungicides in mid-Atlantic soybean.</div>