Herbicide carryover is often a topic of concern when it comes to cover cropping. The best producers are able to successfully use herbicides and covers together. Following these basic rules will help you succeed in this area:
- Read your label. Every chemical has recommended withdrawal period for various crops. From the labeled species, observe the recommendations most similar to your desired cover crop. If a cover crop is not listed, a soil bioassay can be conducted by taking some treated soil, planting the desired cover crop into it, and observing for 2-3 weeks to watch for plant injury.
- Utilize chemicals that have a short residual period in the soil profile.
- If grazing a cover crop after a chemical that has carryover potential, always read the label for grazing withdraw periods. By law, you need to be aware of the effect that these chemicals may have on your livestock. Herbicide Planning Strategy
When planning a weed management strategy that will allow cover crop implementation, consider these concepts:
- Grass Weeds or Volunteer Cereal Control: When the grassy undesirables begin to present themselves, utilize grass-specific herbicides (Select or Clethodim) and follow the cash crop with a primarily broadleaf/legume/brassica based cover crop mixture.
- Broadspectrum Weed Issues: Look for herbicide options that offer control of your targeted weeds but are also labeled for an array of desirable cover crop species. This will allow you to plant a diverse cover crop mixture with species that tolerate the applied herbicide. A good example of a herbicide of this type is Spartan, which uses Sulfentrazone as its active ingredient, but is labeled for over 16 domesticated crops.
- Companion Mixtures: When utilizing companion crops with your cash crop (check your crop insurance regula-tions first!), you must look for herbicide options that are labeled for both the cash crop and the companion crop, or at least will have minimal effect on your companion crop. A great example is utilizing Spartan herbicide with a cash crop of sunflowers, with labeled companion crops of soybeans, chickpeas, peas, cowpeas, flax, some brassicas and more. Another example would be using a product like Verdict which is labeled for corn, popcorn, milo and soybeans, so interseeded cowpeas or soybeans into the corn would work.
- Herbicide Rotation Restrictions in Forage and Cover Cropping Systems – From the University of Wisconsin Extension, this document provides an extensive table on plant back intervals for cover crops with most popular herbicides.
- A Weed Scientist’s Perspective on Cover Crops – This is an excellent resource by Kevin Bradley of the University of Missouri. It summarizes a number of herbicide/cover crop interaction studies.