After the snow melts but before spring green-up is a good time to control weeds that overwinter in alfalfa fields, suggests Bruce Anderson, Extension forage specialist at the University of Nebraska.
Weeds like pennycress, downy brome, mustards, cheatgrass, and shepherd’s purse are common in first-cut alfalfa, Anderson points out. They lower yields, reduce quality, lessen palatability and slow hay drydown. If you walk over your fields during the next few weeks when snow is gone you should be able to see their small, green growth, he says.
"Once alfalfa starts growing, you can’t control these weeds very well without hurting your alfalfa," says Anderson. "However, if you treat your alfalfa as soon as possible during this winter's next spring-like weather, you can have cleaner, healthier alfalfa at first cutting."
Several herbicides can help control winter annual grasses and weeds in alfalfa. They include Sencor, Velpar, Sinbar, Pursuit, Raptor and Karmex. Also Roundup and Gramoxone. They all control mustards and pennycress but Karmex and Pursuit do not control downy brome very well.
To be most successful, though, you must apply most of these herbicides before alfalfa shoots green up this spring to avoid much injury to your alfalfa. During mild late-winter weather would be a great time. If you wait and alfalfa shoots are green when you spray, your alfalfa growth might be set back a couple weeks. If it does get late, use Pursuit or Raptor because they tend to cause less injury to your alfalfa.
"Timing is crucial when controlling winter annual weeds in alfalfa," says Anderson. "Get ready now, in the next few weeks before alfalfa greens up, to take advantage of nice weather when you get it."