Dormant Spraying for Alfalfa Weeds March 2, 2018
With spring warm-up just around the corner, now is a good time to manage weeds in alfalfa before they get a stronghold.
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 snow is gone, you should be able to see their small, green, over-wintering growth.
If your alfalfa variety is Roundup Ready, you can spray almost any time without hurting your alfalfa. However, once conventional alfalfa starts growing, you can't control these weeds very well without also hurting your alfalfa. Fortunately, if you treat your alfalfa as soon as possible during upcoming spring-like weather, you can have cleaner, healthier alfalfa at first cutting.
Before spraying these weeds, be sure they are causing economic damage to your alfalfa. Spraying will give you more pure alfalfa but may cost some in total tonnage.
Several herbicides can help control winter annual grasses and weeds in conventional alfalfa. They include metribuzin, Velpar, Sinbar, Pursuit, Raptor, and Karmex. They all control mustards and pennycress, but Karmex and Pursuit do not control downy brome very well.
To be most successful, you must apply most of these herbicides before alfalfa shoots green up this spring to avoid much injury to your alfalfa. If alfalfa shoots are green when you spray, growth may be set back a couple weeks. If it does get late, use either Raptor or Pursuit because they tend to cause less injury to your alfalfa.
Timing is crucial when controlling winter annual weeds before alfalfa starts to green up. Take advantage of the nice weather when it occurs.