Most cover crop burndown programs begin with glyphosate. But there are a few cover crop species that may offer resistance and require special care, note Bill Curran and Dwight Lingenfelter, Extension agronomists and weed control specialists at Penn State University. So consider these tips before you tank up and head out to spray:

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Glyphosate tends to be more consistent than paraquat. Liberty has a narrow fit, mostly for marestail control, but doesn't add much for cover crops.

Most cover crops are fairly easy to control in a burndown program – if you pay attention to these control details on four cover crop varieties.

Glyphosate guidelines
Cover crops should be actively growing and not covered with crop residue. Sufficient rates generally range from 0.75 to 1.5 pounds acid equivalent per acre. The 22 fluid ounce rate of Roundup or 32 fluid ounce rate of Credit, Rascal,  Clearout, etc. equal 0.75 pound ae.

In general, application alone in good quality water along with appropriate adjuvants (surfactant + AMS) is best. Reducing carrier volume to 10 gallons per acre can increase activity.

But do not add 28% or 32% UAN or other fluid fertilizers to the spray tank. If the water source has a high pH (8 or greater), consider adding an acidifying agent to the spray solution.

Thinking About A Cover Crop? Start With Developing A Plan
Taking time to design your cover crop plan will increase the successful establishment of the crop and potentially allow for improved staggering of fall harvest.

Avoid tank mixing with higher-rate (more than 0.25 pounds) clay-based formulations (WDG, WG, DF, DG, F) like atrazine, simazine, and metribuzin. Other herbicides such as 2,4-D, dicamba, clopyralid, Balance or Corvus, Resolve or Basis Blend, etc. are Okay.

Cover crop knock-out rates
Heribicide performance varies according to cover crop species. Consider these differences:

Winter wheat: Wheat may be less susceptible to glyphosate control than cereal rye. So, make sure you have a sufficiently high glyphosate rate and follow other guidelines to maximize herbicide activity.

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Roundup Powermax's label recommends 32 fluid ounces up 18-inch tall wheat. Performance on wheat is better for applications made before boot stage. Paraquat products can also be effective. But rate, adjuvant, spray volume, nozzles, timing (before tillering or after boot) and the addition of atrazine or metribuzin are important for effective control.

Annual ryegrass: It can be a challenge to control. Glyphosate is the preferred product. Paraquat doesn't provide consistent control.

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Applying during sunny warm days is best; cloudy weather slows uptake and activity. Under cool conditions, it may take 2 to 3 weeks to kill ryegrass. A second application may be necessary.

Small ryegrass is easier to control, but mild air temperatures 1 to 2 days before, during, and 1 to 2 days after application are likely more important. Apply glyphosate at 1.25 to 1.5 pounds ae per acre.

Hairy vetch, red clover, crimson clover, field peas: Glyphosate or paraquat, alone, won't kill most legume cover crops. Tank mixes are important here. Glyphosate should be mixed with atrazine or metribuzin for increased performance. Dicamba (Banvel/Clarity) is most effective and often is a necessary tank-mix partner with glyphosate for red or white clover.

A 2,4-D ester formulation will effectively control hairy vetch and field peas. We're unsure if 2,4-D is adequate or dicamba is necessary for crimson clover.

Both 2,4-D ester and dicamba can be tank-mixed with glyphosate without loss in activity and can be used in corn. Use a minimum of 12 fl. oz./acre of Banvel or Clarity or 2,4-D ester tank-mixed with glyphosate. For corn, apply dicamba or 2,4-D ester 7 to 14 days before planting or 3 to 5 days after planting for greater crop safety. Plant that corn at least 1.5 inches deep.

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Clopyralid is also effective on legumes and is a component of several corn herbicides. However, dicamba and clopyralid aren't suitable for soybeans. And 2,4-D ester (1 pint) must be applied at least 7 days ahead of soybean planting.

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Canola: While it's sometimes included in cover crop mixtures, canola can be somewhat challenging to control. Glyphosate is somewhat weak on it.

Application timing is important. Usually adding 1 pint of 2,4-D ester to glyphosate provides adequate control of smaller canola. Paraquat plus atrazine or metribuzin should also provide good control – again, of smaller canola. Dicamba isn't effective on canola or other brassicas.

Click here to see Penn State's cover crop herbicide effectiveness ratings.