Influence of Winter Annual Weed Removal Timings on Soybean Cyst Nematode Population Density and Plant Biomass

Abstract

Soybean cyst nematode (SCN) is one of the most yield limiting pathogens in U.S. soybean production. Henbit and purple deadnettle are winter annual weeds shown to facilitate SCN reproduction after crop harvest in the eastern Corn Belt. These weeds, along with volunteer soybean that germinates in autumn after harvest, are common to postharvest soybean production fields and provide an opportunity for SCN reproduction and population increase outside of the typical soybean production season. The objective of this experiment was to determine if autumn removal of these weeds and volunteer soybean can influence the winter weed seedbank, plant biomass, and SCN population densities. Microplots were established with or without Lamium spp. and volunteer soybean, and four winter weed removal timings (none, October, December, and May). Dry weights of autumn Lamium spp. were reduced 50% in October when grown in competition with volunteer soybean. SCN juveniles were found in henbit roots at higher densities in October (42 per gram of root) than December (5 per gram of root) and were also found in the roots of volunteer soybean (14 per gram of root) in October. SCN egg population densities were 50% lower in August after the summer fallow period. The results of this experiment suggest that autumn removal of winter annual weeds and volunteer soybean did not reduce SCN populations.