By Chelsey Teachout

Weed control is an ongoing challenge for row crop farmers, and herbicide programs are the primary way many farmers are fighting weeds. However, cover crops such as cereal rye are showing promise as a way to outcompete weeds and allow farmers to rely less heavily on herbicides.

Practical Farmers of Iowa member Sam Bennett of Bennett Farms has been experimenting with cover crops in conjunction with his herbicide program on 80 acres of his family’s sixth-generation farm to help manage weeds.

Bennett farms with his dad and brother outside of Galva in northwest Iowa. He first became interested in cover crops to help build the soil. “We’re no-till, but I thought it’d be a good opportunity to build soil health, break up compaction and add organic matter,” he says. The Bennetts started using cover crops about 15 years ago.

These 80 acres are part of a PFI Cooperators’ Program trial to see how changes in herbicide programs affect weed control while using cover crops. On the trial field, Bennett has been gradually reducing the amount of herbicide he applies and is hoping to reduce it to a burndown-only program. He’s trying to see how weed control for each of the field strips in the trial works side by side.

Reducing need for herbicide

Bennett spends about $35 to $40 per acre for his herbicide program, which includes Prowl, Authority and Metribuzin. And he spends about $20 per acre on cover crop seed. Bennett uses Elbon cereal rye for his cover. His goal is to try to offset the cost of the cover crop with cost savings from reducing the need for herbicide.

Early last September, Bennett had the cereal rye seeded into standing corn using a modified Highboy Hagie seeder. There are a lot of factors that affect how evenly a cover crop will emerge, including seeding rate, rainfall amounts and corn leaf architecture.

“Leaf architecture of a corn plant makes a big difference in how even emergence is and the start of the cover crop,” he says. If you have really broad-shaped corn leaves, the seeds can catch on them. So, rainfall is an important tool to help redistribute the cover crop seed.

Let cover suppress weeds

Bennett let his cover crop grow past the soybean planting date to achieve more growth and better weed control. Because of the cold spring, Bennett says he hasn’t had much luck with pushing up the soybean planting date.

This spring the best growth on the cover crop reached about 2 to 3 feet tall. Bennett collected biomass samples on it for the trial to see how dense it was. On average, the cover crop put on just under 4,000 pounds of aboveground dry matter per acre. The denser the rye, the easier it can outcompete weeds. He often battles weeds such as tall waterhemp, marestail and giant ragweed.

CLEAN BEANS: Bennett’s cover crop trial strips are nearly weed-free in mid-July, as weeds have been suppressed by the rye cover.

“My hope and goal with this cover crop was to produce enough biomass to get it to roll flat, and then I could crimp it,” Bennett says. That amount of cover crop growth did not occur this spring because of the cooler-than-normal temperatures. However, he says the weed control so far has been excellent, and the fields that had cover crops on them are the cleanest.

Teachout is digital media coordinator for Practical Farmers of Iowa in Ames.

Choosing and using cover crop to fight weeds

Cover crops may not be the total answer for weed control, but they can go a long way in helping to keep weeds in check. By planting cover crops, you reduce the density of weed populations, as well as the size of the weeds, explains Sarah Carlson, cover crop specialist with Practical Farmers of Iowa.

While trying to compete with the cover crop, the weed seedlings get less moisture, less nutrients and less sunlight. Because the weeds remain relatively small, the herbicides can provide better control.

To help the cover crop effectively compete with weeds, you need to seed it well in advance of the time the problem weeds begin to emerge, she adds.

Also, choose a cover crop species that produces a significant amount of biomass. Cereal crops, such as oats, wheat, barley, triticale and cereal rye, can do that. But you need to choose a cover crop species that will meet your goals — a species with growth habits that closely match the time when you need to control weeds.

For example, oats won’t overwinter, but they can effectively control weeds if planted early enough in the spring to outcompete spring-emerging weeds. Cereal rye will overwinter and provide weed control in the spring.

For help in choosing cover crops, the Midwest Cover Crop Council has an online decision-making tool to help you select a cover crop species best suited to your region and goals. The interactive website lets you give it your location, crop rotation and objectives. The site will then list the cover crop options that best match your needs. Visit mccc.msu.edu/selector-tool.

Source: PFI