Cover crops offer an effective way to protect against soil erosion in the winter and early spring, but what needs to happen when it’s time to prepare the field for corn or soybean planting?
"There are a number of factors to consider when timing the termination of your cover crops," said Steve Berger, a Washington County farmer from Wellman who has used cover crops on a continuous basis for 15 years on all of his farms.
Many of these management factors were addressed during a recent Iowa Farm Bureau Federation webinar on spring cover crop management. Only winter-hardy cover crops need to be killed with herbicide or tillage in the spring, said Tom Kaspar, a plant physiologist at the USDA’s National Laboratory for Agriculture and the Environment in Ames. While oats and radishes winter kill, Kaspar and Berger offered the following tips for terminating winter-hardy cover crops:
1. Understand the nature of your cover crop. Cereal rye terminates easily from any stage of growth with 32 ounces per acre of generic glyphosate, but annual rye grass is a whole different species. Don’t let it get more than 6 inches tall before terminating it, Berger said. When terminating annual ryegrass, add AMS first, increase generic glyphosate rates to 50 to 60 ounces per acre, use a spray solution of 10 gallons per acre, and avoid tank mixes, Berger added.
2. Watch soil moisture, rainfall and cover crop growth. If spring conditions are dry, plan to kill the cover crop sooner than later so it doesn’t deplete valuable soil moisture, Kaspar said.
3. Pay attention to timing. Kaspar recommends terminating grass cover crops 10 to 14 days prior to corn planting, or before the cover crop is 6 to 8 inches tall. "Before soybeans, the biggest concern is dry conditions," Kaspar added. "If conditions aren’t dry, however, the cover crop can be sprayed three days before planting."
4. Be sure to comply with crop insurance termination dates. Check with your crop insurance provider for more details, Kaspar said.
5. Know when to wait. Vigorous cover crop growth is a good thing. That’s why tiling projects and anhydrous applications can make a difference in the timing of cover crop termination. "Let’s say there’s an area of the field where you’ve got a tile project, and you go over the soil with a blade or field cultivator," Berger said. "Sometimes when you disturb a cover crop like cereal rye, it’s harder to terminate when you spray it afterwards. From the time you work those tile ditches down, maybe wait three or four days to get that rye growing again. Then terminate it, and you’ll have no problem." It’s the same with an anhydrous ammonia application. "The soil disturbance from applying anhydrous will sometimes cause a rye plant to harden off and not respond to glyphosate," Berger said. "Wait awhile to let the rye re-establish before terminating the cover crop, and you’ll be fine."
6. Follow good glyphosate application practices. Berger terminates 99 percent of his cereal rye with glyphosate and encourages growers to respect good glyphosate practices. "Whenever possible, try to spray in the middle of the day when the weather is sunny and warm, there’s little wind and the cover crop is actively growing," said Berger, who watches for nighttime temperatures to warm into the upper 40s.
7. Watch for weed and insect issues. When terminating cover crops, be mindful of controlling winter annual weeds and other yield robbers. "This may mean increasing your glyphosate rate or adding some 2, 4-D or LV6," Berger said. "You might also want to add an insecticide to help control pests."
8. Evaluate tank-mix strategies. Along with glyphosate and an insecticide, Berger sometimes adds residual herbicides to his tank-mix. "There are some risks associated with this, but it’s a risk worth taking," said Berger, who also adds UAN to the mix. His 2015 program for acres going into corn included 17 pounds of AMS per 100 gallons, glyphosate with rates increased to 48 ounces, Harness Xtra 6.0 herbicide at 2.3 quarts, atrazine at 0.65 quarts, bifenthrin insecticide at 4 ounces and UAN (25 pounds of nitrogen per acre) at 7 gallons per acre. "We got along fine and had an excellent kill with this program," Berger said.
His tank mix for acres to be planted to soybeans included 17 pounds of AMS per 100 gallons, glyphosate (4 pounds) with rates increased to 50 ounces, Anthem herbicide at 7.8 ounces, and LV6 herbicide at 3 ounces. "This tank mix also worked very well as a pre-emerge spray trip," noted Berger, who said that he only adds the LV6 in the early pre-plant situations when he’s far enough away from planting.
In many cases, cover crops are terminated within a week or less following these programs. "Maximizing your cover crop investment properly will help you reach your goals of profitable crop production, erosion control and improved soil health," Berger said.
Maulsby is a freelance writer in Lake City.
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