By Jason Johnson

Editor's Note: Jason Johnson, public affairs specialist for USDA's Natural Resources Conservation Service in Iowa, interviewed NRCS state agronomist Barb Stewart and provides the following information.

Many of Iowa's popular winter hardy cover crops like cereal rye, wheat and clover, need to be terminated at least two weeks prior to planting corn and soybeans to minimize yield loss risk. 

As beneficial as cover crops are, killing them is critical, says Barb Stewart, state agronomist with USDA's Natural Resources Conservation Service. "Killing cover crops as late as feasible will maximize plant growth and residual nutrient accumulation," she points out.

CROP INSURANCE CAUTION: There are rules for cover crops regarding crop insurance coverage on corn and soybeans planted following a cover crop. The rules for 2013, set by USDA's Risk Management Agency, say you can't harvest for hay or graze a cover crop past May 10. Also, you can't plant a cash crop into a living cover crop if you want to insure the cash crop for that year.

Stewart adds, however, you need to be sure and allow at least two weeks for cover crops to decompose, release nutrients and recharge soil moisture.

What if the weather forecast predicts a dry spring will continue?

If spring is exceptionally dry, or if the long-range forecast predicts dry conditions, Stewart recommends terminating cover crops when they are 6 to 8 inches tall.

She says small grain cover crops can reduce corn yields similar to the effects of continuous corn. "Plant chemicals called allelochemicals released into the soil can inhibit corn growth," explains Stewart. "This is why terminating the small grain cover crops at least two weeks prior to corn planting is necessary."

Some cover crop species, such as oats, spring wheat, and annual ryegrass, typically do not survive Iowa winters. Brassica cover crops, such as radishes or turnips, should also winter kill in Iowa. However, Stewart says these plants produce hard seeds that can stay viable in the soil for years. "Scout each year in fields where you have grown brassicas," she advises. "Hard seeds may germinate the next spring. Watch these areas for seed germination, and if there is significant germination from hard seed you may need to terminate them."

What's the best method to use to kill a cover crop in spring?

Producers can terminate cover crops with herbicides that are compatible with the spring-planted crop. Harvesting, crimping, or mowing should be used only if the cover crop is mature.~~~PAGE_BREAK_HERE~~~

To maximize soil health benefits from cover crops, Stewart recommends terminating them without tilling the soil. "Cover crops improve overall soil health by adding living roots to the soil during more months of the year and increasing organic matter in the soil," she says. "Tillage destroys all of those natural benefits."

Be careful about crop insurance on corn and soybeans following a cover crop

Farmers should not plant corn or soybeans into a living cover crop, or risk losing out on crop insurance benefits on the corn or soybeans.

Knowing the rules for insuring cash crops following a cover crop is important for successful spring management. From USDA's Risk Management Agency, the 2013 Crop Insurance rules for the region including Iowa, Minnesota and Wisconsin declare that crop insurance can't be attached to a planted crop on acreage for which in the same calendar year:

* A crop (other than a cover crop) reaches the headed or budded stage prior to termination, regardless of the percentage of plants that reach the headed or budded stage; or

* A crop, including a cover crop, is hayed, grazed or otherwise harvested past May 10; or

* A crop, including a cover crop, is not terminated prior to planting.

Basically, these rules for 2013 mean you can't double crop or plant a cash crop into a living cover crop if you want to insure the cash crop for that year. Nor can you harvest for hay or graze a cover crop past May 10. Speak with your crop insurance agent if you have questions or need more information.

Iowa farmers planted more acres of cover crops in 2012 -- about 100,000 acres of covers were planted -- than ever before. By comparison, only about 5,000 Iowa acres were planted to cover crops in 2009. Cover crops are helpful in limiting nitrogen leaching, reducing soil erosion, suppressing weeds, improving soil health, feeding livestock, among other benefits. For more information about cover crop termination, visit your local NRCS office.