Controlling Winter Annuals in Alfalfa

Spring green up is right around the corner. For many it can’t come soon enough.  Producers raising alfalfa may want to pay close attention to their stands this time of year. Before alfalfa plants begin to grow there is a short window of opportunity to control some pesky weeds in our stand, winter annuals.

Plants like henbit, pennycress, shepherd’s purse, mustard, annual bluegrass, and cheatgrass seem to magically appear in our stands about this time every year.  These winter annuals germinate in the fall, lie dormant during winter, then pick up growth quickly in the spring as warm temperatures return.  Greening up before almost any other plants in our fields gives these species a competitive advantage, and they capitalize on it with fast growth and quick maturity, often setting seed before other summer annuals have done much more than starting to grow.

This speedy life cycle means our window for control is limited, especially in alfalfa.  Because we don’t want to damage our alfalfa plant during the fall as it prepares for winter, or later in the spring as it starts new growth, the best window of opportunity is the short time in the spring where winter annuals have started to grow again, but alfalfa is still dormant.

To take advantage we need to act as soon as winter annuals begin to grow.  Scout alfalfa fields and determine if weed pressure is enough to warrant the cost of control.  Weeds can reduce overall yield, lower hay quality and palatability, and slow dry-down time for the first cutting. Producers whose goal is dairy quality hay will most likely find the benefit of control worth the expense.  If the hay is destined for dry cows in a beef herd, the difference between benefit and cost may need a closer examination.

It is also important to identify what species need to be addressed.  Herbicide efficacy varies by species, so picking the product that best controls your problem weed can prevent future applications and save money in the long run.  Need for broadleaf or grass weed control is especially important to identify as some broadleaf products have no action at all on grasses.

Producers with RoundUp-Ready alfalfa varieties can apply glyphosate at almost any time without the worry of damaging their crop.  However, best control will occur when weeds are small and by treating early, you can count on a cleaner harvest at first-cutting.

If we miss the window of opportunity when plants are dormant, select an herbicide that allows application after growth has initiated to minimize damage to the crop.  Most of these products target alfalfa growth under 2-3 inches and have pre-harvest intervals, so do your research before applying.  If you need help selecting the right product for your situation, your local extension office will be happy to connect you with an educator that can provide guidance.

Winter annuals can be a seemingly never ending fight in alfalfa stands, but by being prepared and acting quickly when the time is right, we can take control. 

-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce.  He is based out of the Cedar County Extension office in Hartington.  You can reach him by phone: (402) 254-6821 or email: