Effect of mechanical cutting, planting population and foliar fungicide on soybean white mold and yield

Abstract

<p><em>Sclerotinia sclerotiorum</em>, which causes white mold, is a damaging fungal disease in soybeans [<em>Glycine max </em>(L.) Merr.]. White mold occurs regularly in the upper corn belt of the United States where yield loss from outbreaks routinely occur due to the climate with high humidity and moderate temperatures. Many cultural practices can be implemented to mitigate the negative effect of white mold. This study investigated a novel cultural practice by using mechanical cutting, henceforth referred to as mowing, as a white mold defense practice. Mowing the soybean plant during early vegetative growth alters the plant architecture and growth habit that would allow for better air movement within the canopy, reduce humidity and modify the micro-climate in a way that is less suitable for disease development. Mowing was paired with two other treatments, fungicide application and lowered population density, to observe how treatments interacted. Research was conducted in Iowa, Illinois, Michigan and Wisconsin in 2017 and 2018. The experimental design was a randomized complete block with at least 4 replications. Treatments included mowing, seeding rate (80,000, 110,000 and 140,000 seeds per acre) and fungicide (boscalid, Endura®). Mowing of soybean plants was done at the V4 growth stage when the apical meristem of the plants was removed, and the crop was set back to the growth stage V3. Data collected included yield, response to mowing, disease severity, and plant height. Mowing reduced disease in mowed plots in multiple locations; however, it also reduced yield in all locations. There was less white mold pressure in plots with lower seeding rates and fungicide significantly reduced white mold in two of the locations. These results indicate that cultural practices such as mowing, reduced plant population and fungicide may reduce white mold severity but may not increase yield either in the presence or absence of the crop disease.</p>