CropWatch March 5, 2010: Treat Winter Annuals in Dormant Alfalfa
March 5, 2010
Now may be a good time to tackle problem winter annual weeds in your alfalfa before it starts greening up.
Weeds like pennycress, downy brome, mustards, cheatgrass, and shepherd's purse are common in first cut alfalfa. They lower yields, reduce quality, lessen palatability, and slow hay drydown. If you walk over your fields during the next few weeks when the snow is gone, you should be able to see the small, green, over-wintering growth of these weeds.
Once alfalfa starts growing, it will be more difficult to control these weeds; however, if you treat your alfalfa as soon as possible during the 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, Karmex, Roundup, and Gramoxone. They all control mustard and pennycress, but Karmex and Pursuit do not control downy brome very well.
To successfully control these weeds without injuring your alfalfa, most of these herbicides need to be applied before alfalfa shoots green-up. If you wait to spray until alfalfa shoots are green, alfalfa growth could be set back a couple weeks. If it does get late, use either Pursuit or Raptor because they tend to cause less injury to alfalfa.
Extension Forage Specialist