Integration of Row Spacing, Seeding Rates, and Fungicide Application for Control of Sclerotinia Stem Rot in Glycine max.

Soybean (Glycine max) farmers in the Upper Midwest region of the United States frequently experience severe yield losses due to Sclerotinia stem rot (SSR). Previous studies have revealed benefits of individual management practices on SSR. This study examined the integration of multiple control practices on the development of SSR, yield, and the economic implications of these practices. Combinations of row spacings, seeding rates, and fungicide applications were examined in multi-site field trials across the Upper Midwest from 2017-2019. These trials revealed that wide row spacing and low seeding rates individually reduced SSR levels but also reduced yields. Yields were similar across the three higher seeding rates examined. However, site-years where SSR developed showed the highest partial profits in the intermediate seeding rates. This indicates that partial profits in diseased fields were negatively impacted by high seeding rates, but this trend was not observed when SSR did not develop. Fungicides strongly reduced the development of SSR, while also increasing yields. However, there was a reduction in partial profits due to their use at a low soybean sale price, but at higher sale prices fungicide use was similar to not treating. Additionally, the production of new inoculum was predicted from disease incidence, serving as an indicator of increased risk for SSR development in future years. Overall, this study suggests the use of wide rows and low seeding rates could be useful in fields with a history of SSR, while reserving narrow rows and higher seeding rates for fields without a history of SSR.