Even if you’ve used cropping practices in past years that cut weed-seed production, or mowing to cut weed competition, herbicides are the only means for fully controlling weeds in spring-seeded alfalfa. So says Bruce Anderson, University of Nebraska Extension forage specialist.
“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,” Anderson advises. “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.”