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A number of different crops are potentially available for use as a cover crop depending on the growing season and environment where the crop is to be planted. Cover crops can include legumes (red, berseem, mammoth red, white, alsike, crimson, and sweet clovers, annual medics, cowpea, hairy vetch, alfalfa, birdsfoot trefoil), grasses (annual ryegrass, cereal rye, oats, wheat, sorghum-sudangrass, triticale, barley, rye), brassicas (oilseed radish, mustards, forage turnips, rape, canola) and other broadleaves such as buckwheat. Each species has benefits and disadvantages and must be managed accordingly. The legumes can potentially provide additional nitrogen (Table 1). An excellent tool to help determine which cover crop is best suited for a field is The Cover Crop Decision Tool - Field Crops, which is available from the Midwest Cover Crops Council (www.mccc.msu.edu/index.htm).
Several methods and variations within the methods can be used to seed cover crops. The weight and size of cover crop seeds can vary greatly; therefore, the seeding equipment and management practices should be matched with the seed.1
Overseeding or interseeding should occur when there is enough available light for the cover crop seed to germinate and become established, but late enough that it does not compete with the growing crop. In the northern U.S. and Canada, recommendations based on research suggest that legumes should be seeded between corn growth stages of V-4 and V-6, while annual ryegrass should be seeded between V-6 to V-8.2 In the central Corn Belt overseeding in corn generally occurs at black layer as the crop begins to senesce. In soybean, overseeding is best accomplished when leaves begin to turn yellow. Overseeding may not be recommended if soils are too dry to adequately establish a stand.
Frost-seeding occurs when the cover crop is seeded in late winter to very early spring such as red clover being seeded into wheat in March or earlier depending on geographical location. Seeding can also be accomplished pre- or post-season when the cover crop is seeded before a late-season crop or after the prior crop has been harvested.
Chemical control with a tank mix of a Roundup® brand agricultural herbicide product and 2,4-D ester can provide effective control. Applications should be made to the cover crop when its stage of growth is best for control. Individual state recommendations should be followed.