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Serving: IA

Tips for managing cover crops this spring

herbicide sprayer
TIMING: Iowa State University agronomists generally recommend terminating grass cover crops when they are 6 to 8 inches tall, and to terminate 10 to 14 days before planting corn to protect yield. That time frame is less critical for soybeans.
Farmers are encouraged to share photos of their cover crops on social media.

As the number of Iowa farmers using cover crops continues to grow, it’s important to help make sure they have a successful experience. The Iowa Department of Agriculture and Land Stewardship recently published spring management tips for farmers new to growing cover crops. Farmers who are using cover crops are encouraged to share photos on social media. IDALS will be sharing photos on Facebook and Twitter using the hashtag #FarmersCoverIowa.

“We continue to see significant growth in the number of farmers using cover crops on their farm and also total acreage of cover crops in the state,” says Iowa Secretary of Agriculture Bill Northey. “With the mild winter and good soil moisture this spring, we are seeing very good cover crop growth, and it’s a great opportunity for farmers to share why they are using cover crops through social media. Farmers using cover crops are seeing benefits of reduced erosion, improved water quality, soil health and better weed control. But spring management decisions remain critical to successful cover cropping.”

Timing cover crop termination
It’s important to allow the cover crop to grow as long as possible to maximize the benefits of reducing erosion, improving soil health and helping weed control. This is typically easier for soybeans after winter cover crops because of the later planting date and less potential impact on soybean yields. For corn following a winter cover crop, it’s important to fully terminate a cover crop and provide enough nitrogen at planting. If applying N at planting is not possible, then plan to terminate a cover crop 10 to 14 days ahead of planting. More experienced cover crop farmers may be comfortable with termination closer to planting if they are taking additional steps to manage nitrogen.

This information was put together with the help of the Iowa cover crop working group, which includes representatives from IDALS, Practical Farmers of Iowa, Iowa State University, Iowa Learning Farms and USDA Ag Research Service. More information about including cover crops in your farming operation can be found at Clean Water IowaIowa Learning Farms and Practical Farmers of Iowa.

1. Evaluate for winter kill
The mild winter, coupled with an early spring has provided near optimal conditions for cover crop growth. Cover crop species that may normally winter-kill may have overwintered. Scout your cover crop fields and check the crown of the plant for green plant tissue. Even if the leaves of the plant are brown, double-check whether the crown is brown or green. If the aboveground cover crop is brown and near the soil surface no green plant material is present, then your cover crop winterkilled. Cover crops such as oilseed radish and oats typically winter-kill and then no additional spring management is needed. Other cover crops, such as winter cereal rye, winter wheat and winter triticale consistently overwinter in Iowa.

2. Select termination options
Herbicides, tillage or a combination of the two can be used to effectively manage cover crops in spring. Keep in mind any tillage will reduce the effectiveness of the cover crop residue to protect against erosion and suppress weeds. Tillage termination could also create more difficult planting scenarios so check which implement you are using to reduce cash crop plant stands. Some additional considerations for both methods of termination follow:

• Herbicide. Rule of thumb: Mow the yard once and then get ready to kill your cereal rye. It needs to be growing. For successful herbicide termination, make sure the plant has "greened-up" and it has enough living surface area for the herbicide to work. Experienced farmers suggest spraying during the middle of the day, and if possible, spray when day and nighttime temperatures add up to 100 degrees F. Unless you have experience, separate your nitrogen application from a "burndown" herbicide application or be sure not to dilute the herbicide effectiveness with too much nitrogen as the carrier.

• Tillage. Terminating cover crops with tillage can be effective, but may take more than one tillage pass. Wet periods can delay tillage to terminate cover crops and wet conditions following tillage can allow cover crop plants to survive tillage operations. Also, tilling a cover crop to terminate eliminates the erosion prevention and potential weed control benefit the cover crop would usually provide in the early part of the growing season. Lastly, if spring tillage is a must, make sure to fully bury cover crop root balls that will have dislodged. Double-check planter setup to make sure good seed depth is achieved.

3. Consider nitrogen needs
Winter cereal cover crops effectively scavenge nitrogen and reduce soil available nitrogen in late April and during May. To protect yield, farmers growing corn after a cereal rye cover crop may want to apply 30 to 50 pounds of nitrogen at or near corn planting. This is not additional nitrogen, but within the farmer’s total fertilizer program. Options like starter in a 2x2, nitrogen as the carrier for a weed and feed, or some form of available nitrogen over the top will be important to overcoming soil nitrogen that is tied up early in the season.

4. Evaluate planter setup
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 planter setup and make sure to double-check that the seed slot or trench is properly closed at planting. An open seed slot can be especially damaging to corn seed, while soybean seeds seem to rebound better.

5. Scout for insects
Although rarely an issue, sometimes true armyworm can emerge in cornfields following a winter cereal cover crop. These insects can only be treated once emerged. Plan to scout fields of corn where winter cereal cover crops biomass is thick.

6. Know crop insurance requirements
Crop insurance rules state that a cover crop in Zone 3 (western third of Iowa) must be terminated by the day of cash crop planting. A cover crop in Zone 4 (eastern two-thirds of Iowa) must be terminated within five days of cash crop planting. If using no-till, add seven days to either scenario. More information about insurance requirements are online.

7. Start planning now for cover crop needs this fall
Determine what cover crops work with your current or planned crop protection program. Some residual herbicides have carryover restrictions for certain species of cover crops. Consult with your agronomist or cover crop seed representative to look at your specific management system with the integration of cover crops. Additional information can be found in the following Practical Farmers of Iowa documents on corn herbicides and soybean herbicides.

8. Participate in annual cover crop survey
The Conservation Technology Information Center conducts an annual cover crop survey of all farmers, whether they plant cover crops or not. Farmers can take the 10- to 15-minute survey anonymously to help guide policy, research and education on cover crops nationwide.


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