Consider Cover Crops as Weed Control Tool
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Growers with cover crop experience in the Corn Belt know firsthand the soil health and other benefits the practice brings. Many also see cover crops as a tool in their weed control arsenal.
In her 10 years of research and teaching about cover crops, University of Nebraska agronomist and cover crop specialist Andrea Basche believes that weed suppression can be a goal and a tipping point leading to more cover crop acres in corn and soybeans. (The 2022 Ag Census showed that cover crops were seeded on only 5.1% of U.S. farmland.)
“I hear from farmers doing a lot of cover cropping that they’re achieving valuable weed suppression, learned through experience,” she points out.
Mindset and perspective are essential when using cover crops as a weed suppression tool.
“We have to be realistic, as cover crops add complexity to management as farmers learn a new practice where knowledge, confidence and economics play into decision-making,” she says, pointing to reasons for low adoption of cover crops.
Basche encourages growers to understand that growing a plant (biological tool) to compete with weeds leads to variable outcomes.
“One year, your cereal rye could produce 3,000 pounds of biomass or more and another year, you might achieve 500 pounds biomass, even though you seeded and terminated on the same days,” she says. “But we’ve learned that weed suppression is not all about biomass.”
Improving Herbicide Tools
Cover crops can make weeds easier to control with herbicides even when biomass is diminished. Basche says research shows that cover crops are more effective at reducing weed biomass than weed density. By limiting weed growth — rather than reducing the number of weeds — it’s possible to achieve more effective herbicide programs.
“Since cover crops delay weed emergence and keep weeds smaller, farmers can benefit from the expanded spraying window,” Basche says. Even smaller amounts of cover crop biomass can shade weed seeds to increase seed predation, reduce weed germination and shift weed populations.
Basche says that farmers with years of cover crop experience report other herbicide benefits, like reducing the need for a second application. “So, cover crops are not just a one-year return on investment like nitrogen or fungicide. It’s a longer-term mindset wanting to make this practice work.”
Start Small
Basche says the best way to succeed with cover crops is to start small and ease into management. Consider seeding one, five or 10 acres in a field where weed problems are most difficult. Find a local cover crop mentor or specialist and create a two- to three-year plan.
“By starting small, you have time to work on management while keeping crop profitability risks low. Various issues can arise, like termination, possible yield drag or dry weather that impedes germination or stifles an attempt to plant green,” she says.
A grass cover crop ahead of a legume (soybeans) makes learning management practices easier with less risk of failure. When rotating back to corn, it pays to experiment with seeding into standing corn or right after harvest, depending on the weather. Check the Midwest Cover Crop Council’s ‘Cover Crop Recipes’ page for recommendations by state.
Termination Advice
It’s also good to test different termination timings of a cover crop like cereal rye going into corn planting. Most university specialists recommend terminating cereal rye 10 to 14 days before planting to ensure available nitrogen and water at planting.
More experienced cover croppers have learned how to plant green and then terminate cereal rye before it reaches 12 inches tall, often adding some supplemental nitrogen. This taller cereal rye residue creates an armor on the soil to optimize weed suppression, while holding in moisture for the corn crop.
“Our research with cereal rye ahead of corn showed that planting green during dry years reduced corn yield. We recommend terminating ahead of planting to save moisture for the crop, particularly in drier conditions,” Basche says.
University of Nebraska research has shown success planting green with corn using a legume cover crop like hairy vetch. “Our study demonstrated that we could achieve more hairy vetch biomass by terminating after planting without corn yield loss, and providing additional N into the system,” she says.
Basche firmly believes that cover crops, while challenging, are good agronomy. It’s so important to Midwest row crop production that she created a national cover crop course involving seven universities in 2021.
“What’s most rewarding is we’re now seeing graduates put this cover crop knowledge to work, bringing the next generation of professionals who should be competent and confident in this management practice,” she adds.
Resources:
- Grow Cover Crops in Corn
- Can Cover Crops Lower Your Herbicide Costs in Corn?
- Cereal Rye Cover Crop for Reducing Herbicides in Soybeans
- Using Herbicides and Cover Crops in Corn and Soybeans
- Do Diverse Cover Crop Mixtures Perform Better than Monocultures?
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