It can be difficult to find a comprehensive source of recommendations for the control of all of the possible cover crops prior to planting. Some resources we have used recently:
“Successful termination of cover crops”, Purdue Extension, Pub #WS-50-W, available free online.
“A weed scientist’s perspective on cover crops”, a Powerpoint pdf by Kevin Bradley, University of Missouri Weed Science, available free online. Contains a summary of his research on cover crop termination and effect of residual herbicides on cover crop establishment.
Information we have gleaned on cover crop burndown based on these and various other resources:
- optimal management of cover crops in the spring comes with experience and varies with soil type, weather, etc. Check with other growers/agronomists/consultants who have worked with cover crops in your area of the state since they may have the best knowledge for your situation.
- In general, smaller is better when trying to kill cover crops but applying too early can be detrimental under certain soil moisture conditions.
- Radish and oats typically die on their own over the winter and do not require additional burndown. However, radish that does survive the winter can be difficult to control.
- cereal rye, winter pea, and hairy vetch are relatively easy to kill, while wheat, crimson clover, and annual ryegrass can be difficult to kill.
- Overall, glyphosate is still the most effective herbicide for cover crop control. It does not usually need help to control grasses. Rates should be increased for control of certain grasses, such as annual ryegrass and wheat. Mixing with other herbicides can reduce control of these species, especially under cold conditions. Glyphosate should usually be mixed with a growth regulator (2,4-D, dicamba, clopyralid) for control of legumes and other broadleaf covers.
- Gramoxone can be effective on hairy vetch and cereal rye (bigger is better), and even on small annual ryegrass. Most effective when mixed with atrazine, metribuzin, and/or 2,4-D.
- Liberty is expensive and not usually a good choice for control of covers. Most effective when applied with atrazine during warm, sunny weather.
- In many cases, the POST application of glyphosate in Roundup Ready corn or soybeans will help control covers that the burndown is not completely effective on.
More specifics for a few species:
Cereal rye: up to 18 inches tall, glyphosate (0.75 lb ae/A). Increase rate on taller rye. Antagonism with other herbicides only a minor concern. Gramoxone can be effective on taller plants at high rates, especially when applied with atrazine and 28%. Adequate spray coverage is essential with Gramoxone – at least 20 gpa.
Winter wheat: up to 18 inches tall, glyphosate at 1.1 to 1.5 lb ae/A. Increase rate on taller wheat. Antagonism with residual herbicides and 28% is a concern – apply alone in water for most consistently effective control. Smaller is better. Gramoxone is not consistently effective.
Annual ryegrass: glyphosate, minimum of 1.5 lbs ae/A. Increase rate on larger plants or in cold weather.
Hairy vetch and winter pea: glyphosate (0.75 to 1.1 lb ae/A) plus 2,4-D or dicamba. Gramoxone can control larger hairy vetch – apply with atrazine and/or 2,4-D.
Alfalfa, clover: Glyphosate (1.1 to 1.5 lb ae/A) plus 2,4-D, dicamba, or clopyralid. Clopyralid is very effective on these species.