We’ve often heard from no-tillers that one of the many benefits they see from cover crops is weed suppression, and a Penn State University study currently in progress is confirming just how effective they can be.
In spring 2015, Penn State started evaluating how effectively 1- or 2-species mixes of grass (rye or oats), legumes (hairy vetch or crimson clover) and brassicas (radish) suppressed marestail at the time of a typical spring burndown application before planting.
Preliminary results from the first 2 years of the study show covers provided at least a 75% reduction in marestail populations at the time of a spring burndown, with cereal rye providing the most suppression of the covers. The researchers note that sufficient fertility — especially nitrogen — allowed for vigorous cover crop establishment and growth, which helped suppress weeds.
In addition to a reduction in population, they also found the marestail that was still present at burndown was a smaller size. They believe that spraying smaller-sized weeds will result in greater herbicide control, which could likely reduce herbicide resistance.
These results support what growers are witnessing on their own farms. According to the Sustainable Agriculture Research & Education’s 2015-16 Cover Crop Survey Report, 82% of cover crop users indicated that cereal rye helped reduce weed problems, while 26% reported that cereal rye helped improve control of herbicide-resistant weeds.
Cereal rye has also shown promise in controlling Palmer amaranth. Researchers with the University of Tennessee looked at how cover crops suppressed glyphosate-resistant Palmer amaranth in cotton, and found a grass and legume combination provided the most biomass and reduced emergence by half compared to test plots with no cover crops. They also note that cereal rye and wheat provided the best control 28 days after a pre-emergence application.
“While there was no single solution for season-long control of glyphosate-resistant Palmer amaranth, cover crops used early in the growing season in conjunction with pre-emergence herbicides can help growers diversify their weed management practices to improve sustainability,” says weed scientist Larry Steckel.
Have you seen cereal rye or any other cover crop provide weed control on your no-till operation? Share your success in the comments below.