Cover crops can play an important role in reducing soil erosion and building soil health. There are many options regarding cover crop species, but one of the more popular cover crop choices is cereal rye because it can be planted into the late fall period. Many of our area dairy farmers also plant cereal rye because it provides an option for a spring forage crop before planting a corn crop. Another cover crop option that is used, again for an alternative forage crop before corn planting, is annual ryegrass. Here at the cusp of another planting season, one of the common questions I receive regarding both of these cover crops is how and when to terminate the crop. Let's examine some termination options and considerations for both of these cover crops.
One concern sometimes expressed with cereal rye followed by corn is the potential for germination injury or an allelopathic effect on the emerging corn crop. On-farm trials, farmer experience and research studies are providing information that tells us that although these concerns have merit, there are ways of managing the cereal rye to avoid these issues. Iowa State University did a multiple year study with both growth chamber and field trials to look at the potential for increased seedling disease in corn planted after a cereal rye cover crop. Corn was planted at various time intervals after terminating a rye cover crop. The cereal rye cover crop was terminated from 21 days before planting to one day after planting. Both the growth chamber and field trials showed that under cold, wet conditions conducive to seedling disease development, corn planted less than 10 days after cereal rye termination had more seedling disease, decreased emergence, reduced plant growth and reduced yield compared to corn planted 10 or more days after cereal rye termination. Overall, the Iowa State research results suggest planting corn at least 10 to 14 days after cereal rye termination as a recommended practice.
University of Nebraska research indicates that the worst time to plant corn is five to 10 days after a cereal rye crop is chemically terminated. Paul Jasa, a University of Nebraska cover crop researcher, says that corn could be planted into a living cereal rye cover and the cover could be terminated a couple of days after planting to allow the corn seed to start germinating before the cereal rye dies.
University of Nebraska research has also shown that the chance of germination injury is reduced as planting depth is increased. Growers planting corn 2.5 to 3.5 inches deep have not reported any germination injury after cereal rye crop termination.
I know growers who have a history of successful corn production planting into a mature (5- to 6-foot tall plus) cereal rye cover crop. These growers recommend planting cereal rye at a reduced seeding rate and providing extra, supplemental nitrogen at planting time. Another termination method that can be used on a cereal rye crop once it is in reproductive growth and has a seed head is rolling or crimping either before planting or after planting. This type of mechanical termination also works well in combination with soybeans. For anyone interested, there will be a demonstration of rolling/crimping cereal rye followed by soybean planting at the small grains field day on June 13 at the OARDC Schaffter farm on Oil City Road. Watch for more details in the future.
Annual ryegrass develops an extensive and vigorous root system which is great in terms of building soil quality, but aggressive spring growth can also present some termination challenges. In addition, Italian ryegrass, most often used as an annual ryegrass cover crop, can have resistance to four herbicide sites of action, including glyphosate. Annual ryegrass should be terminated before reaching viable seed production growth stage to avoid the potential of establishing a weed species in future cultivated crops.
The challenge of terminating an annual ryegrass cover crop with herbicides has a lot to do with spring weather conditions. Annual ryegrass can start growing early and herbicide burndown should be done when the plant is less than 8 inches tall and before the first node develops. The issue is that the primary herbicides used to terminate annual ryegrass, especially glyphosate, require warm temperatures, ideally 60 degrees Fahrenheit or warmer, but several days of 50 degree temps can suffice to effectively translocate within the plant. Sunny days are better than cloudy days to make the application. Growers who take a forage harvest of annual ryegrass from the spring growth and then terminate the regrowth report more successful annual ryegrass termination.
A Purdue Extension publication titled "Successful Annual Ryegrass Termination with Herbicides" contains the following herbicide recommendations:
■ use at least 1.25 pounds ae/A of glyphosate (36 fluid ounces of Roundup PowerMax) to terminate annual ryegrass. Under less-than-ideal conditions, rates of 2.5 lbs. ae/A of glyphosate are preferred.
■ Mixing 1 ounce/A of Sharpen with 1.25 pounds/A of glyphosate provided the most consistent control of annual ryegrass at all application timings.
■ Adding 2,4-D, dicamba and Basis Blend did not increase or decrease termination efficacy compared to glyphosate alone.
■ Adding a PS-II inhibiting herbicide (atrazine and metribuzin) can result in antagonism of glyphosate and fail to terminate the annual ryegrass.
For more information about cover crop termination, contact the Wayne County Extension office at 330-264-8722.
Rory Lewandowski is an OSU Extension Agriculture & Natural Resources educator and may be reached at 330-264-8722.