Cover Crop Interseeding to Manage Herbicide-Resistant Weeds

This project explores a potential solution to a practical challenge of using cover crops as part of an integrated weed management program. Such integrated programs contribute to the management of herbicide resistant weeds, which are major problems in grain crop production in Kentucky and throughout the Southern region. Glyphosate-resistant marestail is now widespread in the south and is very difficult to control in no-till soybeans. This weed traditionally emerges in the early spring, though cohorts of fall emerging marestail have been noted recently in Kentucky and other Southern states, necessitating additional fall herbicide applications. Integrating cover cropping with good chemical control may contribute to management of this species (and other winter annuals) as marestail is sensitive to competition when small. However, there are challenges to integrated management of this weed. Timing of cover crop establishment relative to weed emergence is critical. Cover crops are typically drilled after cash crop harvest. Depending on residue cover, soil moisture, and ambient temperature, cover crop establishment and early growth may be limited severely in the fall and ground cover may be slow to develop. If marestail emerges prior to or soon after harvest, it may be well-established by the time the cover crop is established and may not be effectively out-competed. Cover crop interseeding is a technique in which cover crop seed is sown into a standing cash crop. A modified grain drill that plants cover crops into corn when it is about 1’ tall has been developed by researchers and extension agents in Pennsylvania. Since seeds are sown directly into the ground, establishment is less reliant on soil moisture conditions than broadcast seed. Establishing cover crops in this way may improve their competitive ability against weeds, help further protect soil from erosion as continuous ground cover is maintained, and improve excess nutrient capture. This proposal seeks to generate baseline data on this approach in the Southern region. We also seek to draw on the expertise of the forage breeding program at the University of Kentucky to identify cover crop species that are suited to Kentucky and will work well when interseeded (e.g. they are shade tolerant and have low moisture requirements to limit competition with the cash crop). This technique is a great example of Integrated Pest Management—a science-based approach to pest management that addresses environmental, economic, and human health concerns through the potential reduction in herbicide use and improvements in the overall sustainability of weed management. If this technique proves viable in Kentucky, it could reduce or eliminate the need for fall burndown herbicide applications if winter annual weeds are successfully managed by an early-established competitive cover crop stand; contribute to managing glyphosate-resistant fall-emerging marestail and other herbicide resistant winter annuals weeds; and improve delivery of other ecosystem services provided by winter cover crops, including excess nutrient capture, soil erosion prevention, and maintenance of soil organic matter levels.