Double-Crop Soybean Cultivar Response to Foliar Fungicide.

Foliar applied fungicides may provide an opportunity for greater yields in double-crop soybean when environmental conditions are conducive for disease development.  However, cultivars may have varying levels of disease tolerance and respond differently to fungicide application.  Field experiments were conducted in eastern Virginia in 2012 and 2013 to evaluate disease and yield response of maturity group (MG) IV and V soybean cultivars to foliar applied fungicide application in a wheat-soybean double-crop system.  Measurements included normalized difference vegetative index (NDVI), cercospora leaf and stem blight ratings, leaf drop, seed yield and yield response, purple seed stain (PSS), and seed weight and quality.  Fungicide application increased yield at 4 of 6 and 3 of 6 locations for MG IV and MG V cultivars, respectively.  Fungicide increased seed weight at 5 of 6 locations.  Canopy closure and leaf area were limiting factors in yield increase attributed to fungicide.  Cercospora blight was generally controlled by foliar fungicide; however, improved disease control did not always increase yield.  Optimum fungicide timing depended on soybean growth, environmental conditions, and disease intensity, and rate of disease development.  These results should assist research and Extension personnel, crop consultants, industry representatives, and farmers in making agronomic and plant pathology decisions in double-crop soybean production.