Add Cover Crops to Your Weed Control Strategy

Cover crops can serve as a viable solution to help combat pesky weeds

Farmers have heard about the soil health benefits of cover crops for years. Now, some farmers who add cover crops to their rotation also see opportunities for greater weed control. When incorporating a new practice into an operation, it’s important to consider both risks and benefits to decide what works best for each individual field.

Match the Cover Crop with the Cash Crop

Dr. Larry Steckel, row crop weed specialist with the University of Tennessee, has done a lot of research on cover crops. Steckel says there are many different cover crop options for farmers to consider using on their operation.

“We’ve settled on a blend of legumes, like a vetch or crimson clover, mixed with wheat or cereal rye. Cereal rye is better in terms of weed control, but most farmers in my region have wheat in the bin, so it’s economical and easy to get. Cover crop mixtures like this can provide good shade on the ground. It helps combat against horseweed and suppresses pigweed early in the season.”

Steckel says the cover crop really needs to be tailored to the cash crop. “For corn you would want to steer away from grasses. I would use a legume, that’ll help the corn get an early start, which helps in a weed control perspective. For soybeans, I really like grasses, mixed with legumes. You plant soybeans later in the season and by then, you have good growth of the cover crop. Most of the growth happens in April. That gives you good weed suppression in the summer.”

However, Dr. Steckel cautions that there are some instances where cover crops can spur weed growth.

“With just a straight legume cover crop, you don’t get a lot of growth and you don’t shade the ground. It gives off nitrogen and nitrogen helps to promote pigweed seedling growth. With soybeans, you need to have a legume and grass cover crop mixture to get any type of good weed control benefit out of it.”

Cover Crops Help Curtail Weeds

Dr. Steckel says there are three key ways cover crops suppress weeds. In his research, he found these three components combined helped cut down germination of pigweed by up to 50%:

1 – Keep light from hitting the ground. “There’s been a lot of research, particularly on pigweed. If light hits the ground, it promotes germination of pigweeds. Shading the ground with the cover crop and cash crop will help curtail germination, which means you can use less herbicide.”

2 – Soil temperature swings. “We’ve done research that shows pigweed germs at a higher rate if you have a fluctuating soil temperature in a 24-hour day. I did some research simulating a 24-hour day, where the soil temperature goes up until noon when the light is hitting the ground and drops by midnight. We saw higher germination of pigweed with that type of temperature variation, versus a constant temperature. Cover crops help mitigate the natural 24-hour temperature swing you get in soils that aren’t covered.”

3 – The Allelopathy effect. “Cereal rye gives off a chemical from the roots that suppresses other plants from germinating. This isn’t as well known or well-studied, but it does have an impact on seed germination of weeds.”

Herbicide Resistance and Cover Crops

Steckel says because of the weed resistance issues with herbicides, farmers have to implement cultural practices.

“We are losing herbicides to resistance at an alarming rate. Cover crops help you mitigate resistance. If you get a good cover crop, you expose less of the weed population to the herbicide, so you cut down selection pressure and give the herbicide a longer effective life because of it. This is a benefit to cover crops that farmers don’t always think about. It can give farmers a few more years of life to a good herbicide that otherwise they would’ve had resistance to earlier.”

If you’re interested in using cover crops on your farm, start with a few test plots to get a better understanding of how cover crops work with your soil, crop rotation and overall operation.

For more information on cover crops, see https://extension.tennessee.edu/publications/Documents/W417.pdf.

For more information on strategies to manage herbicide resistance, visit www.IWillTakeAction.com.

Links embedded on this page may take you away from the Take Action website. The United Soybean Board/Take Action is not responsible for the content and/or claims made by websites not overseen by the soy checkoff.