Next: killing cover crops

Last fall an estimated 40,000 acres of cover crops were planted in Iowa. A number of Iowa farmers planted a cover crop, usually rye, in fields to help protect against soil erosion over winter. Those that had enough soil moisture had a good stand of cover crops, while others had little to no fall germination.

Winter rye seed will probably still germinate this spring, although with a reduced stand. But the soil is dry throughout most of Iowa. Paying attention to the cover crop’s growth will ensure success when making sure cover crops are a long-term addition to your farming system.

What is the best management for a winter small grain in a dry spring? If you’ve had good fall growth and the spring continues to be dry, you will want to kill the cover crop as soon as it is growing this spring. With several days of 50-degree-F weather, once the ground isn’t frozen, the cover crop will be actively growing and able to be killed by a herbicide application.

“The cover crop should show new growth,” says Tom Kaspar, a cover crops researcher at the National Lab for Ag and the Environment in Ames. “Very early applications when it is cold or turns cold after spraying may not kill the cover crop outright but usually prevents it from growing anymore. Then it’s usually pretty easy to kill it with a second application.” For tillage-only systems, kill the cover crop when the field is fit.

There’s a fine balance in spring between receiving the benefits of soil protection from erosion versus potential problems of the cover crop taking up too much precious soil moisture in a dry spring. Be aware in the spring of conditions to improve your chances of success.

Killing a cover crop

Based on experience with members of Practical Farmers of Iowa, here are some guidelines. If you have a winter cover crop in the field, check it in late March or early April. Make sure you stay on top of cover crop management in the spring.

Practical Farmers of Iowa has worked with a number of farmers in on-farm trials using cover crops. For best success, we recommend the following steps for spring killing of cover crops.

If spring conditions are dry, plan to kill the cover crop sooner than later. If planting corn, kill the cover crop 10 to 14 days before planting corn. If it is cold and early in the season, you want to be closer to 14 days. If it’s warm and later in the spring, you can potentially reduce the number of days the cover crop is terminated before planting. Warm soil and air temperatures seem to solve most of the problems with killing rye and getting the corn up afterward.

If planting soybeans, cover crops can be killed closer to planting. Some farmers are no-till drilling soybeans into a living cover crop, then using a “burndown” herbicide to kill the cover crop one to two weeks following soybean planting. Caution: Try this new method on a few acres as you get started.

Herbicides aren’t the only method for killing a cover crop. Using cattle to graze off the cover in spring, or mowing it followed by tillage can kill cover crops.

If using tillage only, don’t let the cover crop get taller than 6 inches.

If using herbicides, apply the legal labeled rate and pay attention to weather conditions before spraying.

Check out PFI’s Cover Crop Business Directory to find area businesses that can custom-kill a cover crop in your field. The directory includes a list of aerial applicators and seed houses that can help you add the practice of growing a cover crop to your farming operation.

To print the directory or read it, go to www.practical

Carlson is research and policy director for Practical Farmers of Iowa in Ames.


This article published in the March, 2012 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2012.