Oral: Schroth Faces of the Future Symposium: Epidemiology and Management
Integrated disease management for optimizing soybean yields and profitability.
H. MEHL (1) (1) Virginia Tech Tidewater AREC, U.S.A.
Over the past decade, soybean producers have increased inputs, including foliar fungicides, to maximize yields. Typically, fungicide applications are made at beginning pod (R3), but yield responses are inconsistent. One contributing factor may be application of fungicides when disease pressure is low and conditions do not favor disease development. A second is the occurrence of fungicide resistant pathogens. Objectives of this work were to 1) develop a weather-based decision aid for foliar fungicide applications in soybean, 2) quantify frequencies of fungicide resistant pathogens, and 3) assess profitability of different foliar fungicide programs. R3 and weather-based fungicide applications were compared at a total of 15 on-farm locations in 2014 and 2015. Dominant foliar diseases were frogeye leaf spot (Cercospora sojina) and Cercospora blight (C. kikuchii). Yield response to fungicide applications was significant in 5 of 15 trials. R3 applications were equal to or better than weather-based applications, but yield response was greatest when weather conditions conducive to disease development occurred within 7 days of R3. Based on a survey of C. sojina populations in Virginia in 2015, 25% of the population had the mutation conferring resistance to QoI fungicides. Implications of environmental conditions and fungicide resistance for cost-effective, sustainable management of soybean foliar diseases will be discussed.