Cover crops are an accepted integrated weed management practice for their ability to reduce emergence and growth rate of driver weeds such as Palmer amaranth and waterhemp. However, there is little information about how cover crops affect the viability of weed seeds present in the soil. Reducing the weed seedbank has the potential to improve management of herbicide-resistant weeds by reducing weed density in the years following cover crop use. This project will investigate Palmer amaranth and waterhemp seed germination following burial in plots with and without a cereal rye cover crop. The study will be conducted in five states, with two locations in Kansas and Wisconsin. Germination results will be evaluated in the context of soil temperature and moisture at the field sites.

Compare the effects of a cereal rye cover crop prior to soybean on weed seed germination and viability over time.

Data from the study will be shared with farmers through the investigators’ extension activities, including field days, newsletters, social media, and radio. Less traditional outreach, such as webinars and podcasts will be used as well.

Updated April 1, 2022:
Palmer amaranth and/or waterhemp were collected from all states and shipped to KSU during fall of 2021. Seeds were cleaned, packaged, and returned to all states and planted as planned. Weather data are being monitored at each site, and communications have been initiated regarding retrieving seeds prior to soybean planting.

Updated March 17, 2023:
Samples that were collected at the time of soybean planting and harvest have been collected and analyzed. The graduate student managing the project is currently synthesizing data for her M.S. thesis. One collection date remains (the 12 month collection) and these are beginning sent to the lab. A copy of the poster presented at WSSA (and recognized as first place in the division) is attached. As described on the poster, cover crops are changing the weed seedbank. Cereal rye increased the dormancy of amaranth, probably extending the time that management is required. Cereal rye increased the viability of two waterhemp populations, which may mean larger populations will emerge in the crop following soybean. These results illustrate the need for more research to verify this observation and determine contributing genetic and environmental factors.

View uploaded report

Seven months after burial of weed seed packets, a cereal rye cover crop had no effect on the seedbank viability of seven Amaranthus spp populations across seven states. At 12 months after burial, when analyzing each population individually, there was an effect of cover crop on seed viability of Missouri and Indiana waterhemp. These two populations exhibited higher viability in cover crop than with no cover crop treatments. Moreover, seed dormancy was also impacted by burial location and removal timing at several locations. However, Palmer amaranth from North Dakota had greater dormancy under cereal rye. These findings are contrary to our hypothesis, that an expected increase in microbial activity would result in seedbank decay.

A better understanding of seedbank dynamics of Palmer amaranth and waterhemp will improve weed management programs designed for multiple years of a cropping system.