Oklahoma State University Stillwater, OK
Oklahoma Alfalfa Oklahoma Cooperative Extension Service Oklahoma Agricultural Experiment Station

Weed Control During Mild Winters
Mild winters allows cool-season grasses and broadleaf weeds to continue active growth all winter. There is also a lot of regrowth alfalfa from last fall in established stands that is still green. This means that dormant season herbicides (such as SINBAR and VELPAR) should be applied as soon as possible, hopefully before alfalfa begins active spring growth.  Some cool-season weeds can be controlled in alfalfa planted last fall with postemergence herbicides. Examples are -  Tansy mustard and cutleaf eveningprimrose can still be controlled with BUTYRAC  Ryegrass and still be controlled with POAST PLUS.  So you should scout your fields now and get ready to spray these weeds on the next warm spell, providing we don't get some zero type weather that damages the top-growth. You can check on the presence of weeds while you are getting your soil samples.  It is important to remember that most annual cool-season weeds (both grasses and broadleaf weeds) emerge in the fall at the time that alfalfa emerges and are easiest to control in small seedling or rosette stage in the fall. Some weeds can still be controlled when the weed plants continue growing in late winter or early spring. This normally is the same time as "green-up" of wheat, and that is starting to happen now.  Herbicides applied on a warm "shirt sleeve" day during this "green-up" period are usually the most effective. Soil moisture also needs to be good at time of spraying so weeds will be actively growing.
Jim Stritzke, Alfalfa Weed Control Specialist  Department of Plant and Soil Sciences  Oklahoma State University

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