Terminating cover crops
By MEAGHAN ANDERSON
Interest in growing cover crops is continually increasing across Iowa. The final step in successfully implementing this strategy is terminating the cover crop at planting. The best cover crop termination method depends on the type of cover crop used. Cover crop species will fall into two categories: winter-killed or overwintering. The ability of a cover crop to overwinter is strongly influenced by environmental conditions during the winter.
Crops that overwinter require termination in the spring. Termination options are relatively limited in the spring and include mowing, rolling or roller-crimping, and herbicide application. Tillage or grazing are sometimes used for this purpose, but these methods are less consistent than the other strategies for terminating a cover crop.
If farmers are interested in terminating their cover in early spring, herbicides will be their best bet. Herbicides provide the most flexibility in cover crop termination timing, but they do not come without risks. Cover crops generally have a dense canopy of rapidly maturing plants in the spring. That, combined with cool temperatures typical of late April and early May, creates an opportunity for termination failure.
Herbicide choices for spring cover crop termination are relatively few, and limited information is available to determine the effectiveness of burndown treatments on less common cover crop species.
What the research shows
Kevin Bradley, a professor at the University of Missouri, found that hairy vetch, cereal rye and Austrian winter pea were relatively easy to control with herbicides. Other species, including annual ryegrass, wheat and crimson clover, were more difficult to control. More specific information regarding Bradley’s research is at the website weedscience.missouri.edu.
Research shows that glyphosate, glufosinate or paraquat provide the most consistent control of grass cover crops. Glyphosate generally allows termination earlier in the spring under less-than-ideal weather conditions. Contact herbicides like glufosinate and paraquat are most effective on small plants. Bradley’s group had the most success terminating legumes like hairy vetch and Austrian winter pea with combinations of glyphosate or paraquat and a growth regulator herbicide, such as 2,4-D or dicamba.
Keep in mind that less-than-ideal weather conditions can wreak havoc on herbicide effectiveness. The following tips should help when planning your spring sprays to terminate a cover crop:
• Whenever possible, spray in sunny conditions when daytime temperatures are above 60 degrees F, the cover crop is actively growing, and nighttime temperatures will be above 40 degrees.
• Skimping on herbicide or adjuvant rates is not a good idea during the cool conditions and dense canopies typically encountered during cover crop termination.
• Follow herbicide label instructions for appropriate adjuvants, mixing order and application instructions, including spray volume, nozzle type and environmental considerations.
• Include only what is necessary for the cover crop termination, as the addition of off-label adjuvants or other herbicides may reduce spray efficacy.
• Check herbicide labels for restrictions to planting corn or soybeans following application in order to avoid injury to your cash crop.
• Consult an expert when you’re not sure — better safe than sorry.
Anderson is an ISU Extension field agronomist. Contact her at email@example.com.
Cereal rye cover crop
This article published in the January, 2016 edition of WALLACES FARMER.
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