Field Evaluation of Label-Recommended Contans® Application Rates and Timing for Sclerotinia Stem Rot Management in Soybean

Sclerotinia stem rot (SSR) is a major soybean disease caused by the fungus Sclerotinia sclerotiorum and can reduce both soybean yield and quality. This study evaluated the effectiveness of Coniothyrium minitans, a mycoparasite of S. sclerotiorum formulated as the commercial product Contans®, applied at label-recommended rates ranging from 1.12 to 4.48 kg ha -1 following label-permitted timing recommendations, with sequential applications at planting and one month after planting across two soil types in Wisconsin. Although treatment effects were not statistically significant, numerical differences were observed that warrant further investigation. Higher application rates at planting may reduce SSR incidence and help preserve yield in the low organic matter sandy soils at Hancock, while providing partial disease suppression and moderate yield benefits in the high organic matter silt-loam soils at Arlington. The limited efficacy observed in this study may be attributed to the timing of applications, which, likely provided insufficient time for sclerotial colonization prior to the soybean crop being susceptible to infection by S. sclerotiorum. Consequently, extending the interval between application and planting may be necessary to achieve effective disease suppression. Adjusting application timing, such as in the fall, may improve efficacy by allowing greater sclerotial degradation prior to planting. Collectively, these findings highlight the need to further refine label recommendations to improve the reliability and consistency of C. minitans based SSR management.