Effects of Mowing, Seeding Rate, and Foliar Fungicide on Soybean Sclerotinia Stem Rot and Yield

Abstract

Sclerotinia stem rot (SSR or white mold), caused by Sclerotinia sclerotiorum (Lib.) DeBary, is an economically important fungal disease of soybean. SSR routinely causes yield loss in the upper Corn Belt of the United States due to wet, humid conditions that coincide with moderate temperatures. This study investigated the novel cultural practice of mechanical cutting, or mowing, as an SSR management practice across multiple seeding rates. Mowing soybean during early vegetative growth alters plant architecture and growth habit. This results in a microclimate within the canopy less suitable for disease development. Field trials were conducted in Iowa, Illinois, Michigan, and Wisconsin in 2017 and 2018. Experimental design was a randomized complete block with four replications. Treatments included mowing (mowing and no mowing), seeding rate (197,684, 271,816, and 345,947 seeds/ha), and fungicide application (boscalid, Endura, and no fungicide). Soybean was mowed at approximately the V4 (four unfolded trifoliate leaves) growth stage. Mowing reduced disease in multiple locations; however, it also reduced yield in most of the locations. In general, there was less SSR in plots with lower seeding rates. Fungicide significantly reduced SSR in two of the five site-years for which disease was observed. Significant yield response to fungicide was also observed in two of the nine total field trials. Results indicate cultural practices such as mowing and reduced seeding rate can decrease SSR severity but also can impact potential yield. Additionally, yield response to SSR management practices may not be observed if disease is absent or at low levels.