Here at Iowa Learning Farms, we love seeing those fields of lush green cover crops out on the land! Across the state, planting is underway or slated to commence soon, which means that it’s also prime time for cover crop termination.
First things first — you want to make sure that cover crop will indeed be killed. Failure to completely control cover crops results in them acting as a weed and competing with your crop.
We’d like to take this opportunity to share a few reminders and pointers to make termination as effective as possible. The tips included below come from Terminating Cover Crops – What’s Your Plan?, prepared by Meaghan Anderson, Iowa State University Extension and Outreach field agronomist in east central Iowa.
Iowa State University researchers generally recommend terminating the cover crop with herbicide 10 -14 days prior to planting corn. Prior to soybeans, hold off on cover crop termination as long as possible… terminating just one day prior to planting offers big benefits in terms of biomass production and nitrogen retention (see our previous blog post Let it GROW, Let it Grow!). Always check with your crop insurance agent for their cover crop termination requirements prior to planting corn or soybeans.
You’ve got choices… regardless of the method chosen, the effectiveness of termination depends on the cover crop species and its growth stage as well as the conditions in the surrounding environment.
Burndown with an herbicide is the most common termination method across the state. Translocated herbicides, like glyphosate, are most commonly used for terminating overwintering cover crops.
For the most effective herbicide application, spray on a sunny afternoon when temperatures are above 60°F, plants are actively growing, and nighttime temperatures stay above 40°F. Avoid spraying in the early morning or evening hours.
Alternatively, contact herbicides like paraquat and glufosinate can be utilized. However, these contact herbicides only affect the parts of the plant they come into contact with. Overwintering cover crops may not be well-controlled with early applications of contact herbicides; this could be because the plants are already too large or growing too quickly (i.e. contact herbicides could be a big challenge with the abundant cover crop growth that was observed this year!).
Check out Anderson’s article for additional information on herbicide rates, formulations, and more.
Termination via rolling or roller-crimping can reduce dependency on herbicides during corn and soybean production. Effective termination with this method is dependent upon the proper timing of the crimping for the cover crop species present. Examples of cover crops that can be controlled with rolling/crimping include hairy vetch (at full bloom), barley, triticale, or cereal rye (all at milk or dough stage). For cereal rye, it is recommended to wait until the rye has shed pollen to get a consistent kill with a roller/crimper.
Tillage is another alternative. However, multiple tillage passes may be necessary to terminate the cover crop, which can negate the benefits the cover crop is providing to soil health and can leave the land more vulnerable to erosion.
Regardless of termination choice, it is important to have a plan in place to minimize problems this spring. Following termination, be sure to check fields for regrowth or skipped areas that need further attention. This will allow for a successful cover crop termination, and, hopefully, a successful cropping season this summer. Read more at Terminating Cover Crops – What’s Your Plan?.