Good management, possibly aided by herbicides, can reduce the amount of foxtail, crabgrass, pigweed and other weeds in alfalfa fields, says Bruce Anderson, University of Nebraska Extension forage agronomist.
The best way to start, he says, is to keep alfalfa thick and thrifty so it will compete aggressively with invading weeds.
“Thick initial stands and good soil fertility are needed,” says Anderson. “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 weeds don’t get much time to become a problem. Unfortunately, this method is easier said than done, and forage quality will be lower since harvest occurs after bloom begins.”
Herbicides are another option. Roundup works great for Roundup Ready varieties. In conventional alfalfa, Select Max and Poast Plus work well on seedling grasses less than 4” tall, and alfalfa tolerates both herbicides very well. Neither has any soil residual activity, so good plant coverage is necessary and you may need to repeat the spraying if new grasses emerge.
For broadleaf weeds, Raptor and Pursuit are your best choices, says Anderson. They, too, need to be applied before weeds are 4” tall. Both have some residual activity so you can apply them a little early and still get control of many later-emerging weeds. They will, however, also set back your alfalfa a little bit, he warns.
“If weedy grasses or broadleaves are a problem in your hay, thick and vigorous alfalfa stands and some well-chosen herbicides can help you get it under control,” says Anderson.