Posted April 17, 2015

As the number of Iowa farmers using cover crops continues to grow, it’s important to help make sure these farmers have a successful experience and Iowa Secretary of Agriculture Bill Northey is offering several spring management tips for farmers new to growing cover crops.

1) Evaluate for winter kill – If the above-ground cover crop is brown and there’s no green plant material near the soil surface, then your cover crop winter-killed. Cover crops such as tillage radishes and oats typically winter kill and then no additional spring management is needed. Other cover crops, such as winter or cereal rye, winter wheat, triticale and barley consistently over-winters in Iowa. In late March, double check plant stems near soil surface to see if the plant has survived.

2) Termination options – Herbicides, tillage or a combination of the two can be used to effectively manage cover crops in the spring. Keep in mind any tillage will reduce the effectiveness of the cover crop residue to protect against erosion and suppress weeds. Some additional considerations for both methods of termination follow:

Herbicide
For successful herbicide termination, make sure the plant has “greened-up” and 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 air temperature is at least 45 or 50 F. Unless you have experience, separate nitrogen application from a “burndown” herbicide application.

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 benefit that the cover crop would usually provide in the early part of the growing season.

3) Consider nitrogen needs – Cover crops effectively sequester nitrogen and as the plant residue breaks down it will release its nutrients, making them available for the crop later in the season when they need them the most. However, there is the potential for lower available nitrogen early in the growing season, especially following an overwintering grass cover crop like cereal rye. To protect yield, farmers growing corn after a cereal rye cover crop may want to apply 30-50 lbs. of nitrogen at or near corn planting. This is not additional nitrogen, but within the farmer’s total fertilizer program.

4) 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 2/3rds of Iowa) must be terminated within 5 days of cash crop planting. If using no-till add 7 days to either scenario.

5) Start planning now for cover crop needs this fall – Determine what cover crop(s) 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 and/or cover crop seed representative to look at your specific management system with the integration of cover crops.

This information was developed with the help of the Iowa cover crop working group, which includes representatives from the Iowa Department of Agriculture and Land Stewardship, Practical Farmers of Iowa, Iowa State University, Iowa Learning Farms, and USDA Agriculture Research Service. More information about incorporating cover crops into your farming operation can be found at http://www.extension.iastate.edu/ilf/.