Controlling Winter Annuals in Alfalfa this Fall

Controlling Winter Annuals in Alfalfa this Fall

Abundant moisture and moderate temperatures have blessed many of the state's alfalfa fields this fall. Unfortunately, conditions that are optimum for a good stand of alfalfa are also optimum for developing a good stand of winter annual weeds. Pennycress, mustards, henbit, and downy brome may be getting a foothold in your alfalfa this month.

While not visible from the road, if you check fields more closely, you may find small groups of henbit plants or mustard rosettes or short grass seedlings of downy brome. This robust start suggests heavy weed growth next spring.  If left uncontrolled, they could grow rapidly, reducing alfalfa yield, thinning stands, and lowering forage quality.

To avoid next spring's weed infestation, spray fields before soils freeze. Probably the three best herbicides to use right now are metribuzin, Sinbar, and Velpar.  All three do an excellent job of controlling pennycress, mustards, and downy brome. If henbit is your biggest problem, consider Raptor.

Delaying weed control until next spring can become complicated. Spring spraying must be done before alfalfa greens up or alfalfa will be injured.  Usually, there are only a few days in spring when alfalfa is dormant, the weeds are actively growing, and it's not too wet or windy.  Missing this application window can give winter annuals a jumpstart in the spring. Then many times, fields don't get sprayed at all or they get sprayed late and alfalfa suffers some setback.

Bruce Anderson
Extension Forage Specialist