Controlling Postemergence Weeds in Alfalfa

Controlling Postemergence Weeds in Alfalfa

June 6, 2008

Are weeds appearing in your new alfalfa? Seedlings compete poorly with weeds and if weeds get thick, alfalfa will suffer. While control decisions can be difficult, timely measures will be important to your alfalfa's sustainability.

When weeds — especially broadleaf weeds — threaten seedling alfalfa, one option is to mow. Be sure to adjust mowing height so several leaves remain on the plant and seedlings can regrow rapidly. Also, mow weeds before they are so tall they produce a lot of clippings that could smother small seedlings.

Another control measure is to spray broadleaf weeds, using Buctril, Butyrac, Raptor, or Pursuit. Buctril controls most small broadleaf weeds, but alfalfa injury can occur when temperatures exceed 80°F. Since those temperatures are normal right now, it might be better to use Butyrac, Raptor, or Pursuit. These herbicides control most broadleaf weeds less than three inches tall and Raptor and Pursuit offer soil activity to control weeds through the season.

Still, mowing can be as good or better than herbicide treatments, although it isn't very effective with grassy weeds. Use Poast Plus or Select to kill unwanted grasses and spray before they are 4 inches tall or control will be spotty.

Weeds slow growth of new alfalfa by shading and competing for moisture. You can prevent these problems by acting quickly to exam your fields and control weeds as needed.

Bruce Anderson
Extension Forage Specialist