April 9, 2010

Alfalfa seedlings grow slowly and many weeds grow quickly, robbing alfalfa of moisture, nutrients, and light. Uncontrolled, weeds can cause thin stands, weak plants, and lower yields.

Cropping practices that reduce weed seed production during the years prior to planting alfalfa help reduce weeds when alfalfa is planted. Also, timely mowing reduces competition from many weeds. Even with these measures, herbicides are the only means for fully controlling weeds.

Options

If you expect grasses like foxtail or crabgrass be a problem in new alfalfa, use a pre-plant incorporated herbicide like trifluralin, Balan, or Eptam. These herbicides control grasses and many small-seeded broadleaf weeds like lambsquarter. Some larger-seeded broadleaves like sunflower will not be controlled, but you can mow those weeds later for good control.

It's great if you can get your alfalfa started without the use of herbicides, but if you have escapes, postemergence herbicides like Buctril and 2,4-DB will control broadleaves, Poast Plus and Select will control grasses, and Raptor or Pursuit will control a combination of weeds. In all cases, weeds need to be sprayed when they're still small according to label rates and conditions.

Bruce Anderson
Extension Forage Specialist