Controlling Grasses in Alfalfa

June 3, 2015

Wet soil in alfalfa fields right after cutting will certainly do one thing — help weedy grasses like foxtail and crabgrass grow.

The best way to control grasses is to keep your alfalfa thick and thrifty so it will compete aggressively with invading grasses.  Thick initial stands and good soil fertility are needed.  In addition, harvest alfalfa only after it begins to bloom or when new shoots appear at the base of the plants.  Then alfalfa should regrow rapidly so grasses don't get much time to become a problem.

Unfortunately, this is often easier said than done.  It also may sacrifice some forage quality since harvest occurs after bloom begins.  Thus, this method may not solve all your problems.

Herbicides are another option for controlling grasses in alfalfa. Roundup® works great, but only for Roundup Ready® varieties.  In conventional alfalfa, two herbicides that control annual grasses well are Select Max and Poast.  These herbicides work well on seedling grasses that are less than 4 inches tall, and alfalfa tolerates both herbicides very well.  Another herbicide option is Gramoxone Extra. Gramoxone burns back top growth of all green plant material.  This will kill most annuals like foxtail, but it also can injure alfalfa regrowth that has already emerged.  Therefore, only use this product immediately after harvest and before any new regrowth shoots appear.  None of these herbicides have any soil residual activity, so good plant coverage is necessary and you may need to repeat the spraying if new weeds emerge.

Bruce Anderson
Extension Forage Specialist