Cover crops planted last fall need to be managed this spring. How to successfully manage cover crops in spring will differ based on the fall planting date, spring growth conditions and goals established by the farmer.

The Iowa Department of Agriculture and Land Stewardship, which coordinates the Iowa cover crop working group as part of the Iowa Conservation Initiative, offers information and resources to help farmers manage cover crops this spring. 

“Cover crop acres in Iowa have seen a 256% growth from 2012 to 2017, according to the U.S. Census of Agriculture,” says Iowa Ag Secretary Mike Naig. “Cover crop acres saw another increase last year, boosted by the record number of prevented planting acres for corn and soybeans due to last spring’s wet weather and flooding. Many of the prevented planting acres ended up being seeded to cover crops.” 

In addition to enhancing soil health and improving water quality, cover crops have benefits for weed control and can provide forage for livestock. “It’s important to follow best practices in order to maximize your return on investment,” Naig says. “There are a lot of novice cover croppers this spring, as a result of the increased prevented planting acres for row crops last year.” 

Follow recommendations 

Some cover crops will winter-kill, leaving only the crop residue to manage in spring. But for common overwintering covers like cereal rye, wheat or hairy vetch, a lot of work lies ahead before the spring crop can be planted. By following these steps suggested by IDALS and the Iowa cover crop working group, farmers can maximize cover crop benefits while protecting cash crop yields: 

1. Evaluate for winterkill. Scout the cover crop fields and check the crown of the plant for green plant tissue. If the leaves are brown and there is no visible green material near the soil surface, the plant may have winter-killed. Oilseed radish and oats typically winter kill and do not need to be terminated. Winter cereal rye, winter wheat and winter triticale often need to be terminated in the spring.  

2. Consider termination options. The Conservation Systems Best Management Practices Manual provides termination guidelines with the intent of minimal impact to cash crops that follow cover crops. Applying herbicides or using a roller can be an option for termination. Tillage can also be used but is not recommended because planter challenges may occur. Tillage also disrupts the cover crop residue and makes it less effective in preventing soil erosion and suppressing weeds.  

If tillage termination is required, more than one pass may be needed to effectively terminate the cover crops. If herbicides are used to terminate the crop, it is best to spray when the crop is actively growing, during the middle of the day and when overnight temperatures are above 40 degrees F. 

3. Allow for growth. To see maximum benefits in the field, allow cover crops to grow as long as possible. Plan to terminate cover crops near soybean planting dates. If planting corn for the first time after an overwintering cover crop, terminate 10 to 14 days before the estimated corn planting date. 

4. Adjust planter setups. A field planted after a winter cereal cover crop will be in a different condition than a tilled or no-till field with no cover crop. Evaluate the planter setup and make sure that the seed slot or trench is properly closed at planting and seeds are at proper depth. An open seed slot can be especially damaging to corn seed. 

5. Understand crop insurance requirements. Crop insurance plans will mandate when cover crops must be terminated. Some policies require that cover crops are terminated five days before planting your cash crops. These timelines will vary based on insurance policies, planting zone and whether tillage is used. Contact an insurance agent to discuss the details of a policy. 

6. Plan ahead for future planting. Cover crop management plans may need to be adjusted based on type of cover crop planted and how it was terminated. For example, some residual herbicides have carryover restrictions for certain species of cover crops. Talk to an agronomist or cover crop seed representative about specific management systems and how to integrate cover crops. 

IDALS offers annual funding to assist farmers with implementing cover crops into their operation. To learn more or participate in the cost-share opportunities, visit your local soil and water conservation district office.  

How about ‘planting green’? 

There are several ways to terminate a cover crop. You can use tillage, crimping or spraying the cover with herbicide before planting corn or soybeans. Planting the spring row crop into a live, growing cover and spraying it shortly afterward, called “planting green,” is another option. 

For first-time cover croppers, and particularly those planting corn, terminating before planting is probably the safest bet, says Mark Licht, Iowa State University Extension cropping systems agronomist. If you choose this option, try to terminate the cover at least two weeks before planting to give it plenty of time to dry down before you plant the row crop. Some farmers who plan on using tillage to kill a cover crop spray it first with herbicide if the cover has grown very tall and thick before the farmer can get into the field with tillage equipment. 

What can you do if wet weather doesn’t permit this timely termination? Planting into a living cover crop is possible, and the living cover crop can actually help dry the soil as it pulls moisture from the ground. If you use this option, time the termination of the cover crop so it takes place between the day of planting and no more than a day or two after, Licht says.

You don’t want the cover crop to continue growing after you plant the corn or soybeans because then it will just act like a bunch of big weeds competing with your cash crop. Soybeans work better than corn for planting green, as they are more flexible, and the biomass from the cover crop residue provides more help to suppress weeds in beans.