Winter Cover Crop Impacts on Weed Dynamics in Eastern and Central Nebraska

Reducing tillage in cropping systems causes weed management to be dependent on chemical and cultural methods for weed control. Over time, herbicide-resistant weeds have developed due to the continuous selection pressures from herbicides, particularly in the Midwest Corn Belt. Integrated weed management strategies, such as cover crops, can be used to mitigate some of these issues. Cover crops are primarily known for their soil health benefits, but there is evidence that cover crops can suppress weeds. However, less research has been done at the field-scale level to address cover crop impacts on the weed seedbank and aboveground weeds during the growing season. In response, two experiments were designed to investigate above and belowground weeds in eastern and central Nebraska. The soil seedbank was germinated from soil samples and weed density and biomass were measured at two points during the growing season. Our results show that cover crops did not influence the total seedbank density, but increased the density of Amaranthus spp. seeds in the seedbank. Aboveground, reductions in weed density and biomass reductions occurred at two sites. More importantly, larger pigweed seedbank densities in the cover crop treatments were not expressed aboveground, signifying cover crop suppression of the weed seedbank through reduced germination withdrawals. This research provides insight on above and belowground weed dynamics under cover crops and shows that cover crops may be a viable integrated weed management tool for Amaranthus spp. management and mitigating risks of herbicide resistance over time by preventing seedbank withdrawals through germination. Advisor: Andrea D. Basch