Troublesome weeds in alfalfa: Identification and management

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included. 

I have received a number of questions lately about a couple of weeds in alfalfa that are becoming more common and difficult to control. Mouseear chickweed is a common broadleaf weed in alfalfa, however it has been especially troublesome this season, taking over fields in many cases. Roughstalk bluegrass, a perennial bluegrass species, has emerged this season to become a concern for growers across the state, primarily in the middle of the state and the Thumb region. Roughstalk bluegrass grows upright from one to three feet in height with stems that are covered with many small hairs, brownish-purple bands around the nodes, and a large membranous ligule (four to six mm). It also has the boat-shaped leaf tip common to other bluegrass species, hairy leaf blades that are short (two to seven inches long), and above ground stolons. Roughstalk bluegrass is a problem in alfalfa because it matures before cutting becoming coarse and ultimately reducing palatability and quality of the hay.

Cutting alone should reduce mouseear chickweed and roughstalk bluegrass competition for the remainder of the season; however if you feel the need to control these weeds, several herbicides can be utilized. These herbicides are mentioned in a previous CAT Alert article entitled “In-season Weed Management in Alfalfa.” Herbicide recommendations, rates, and rotation restrictions can be found in 2009 Weed Control Guide for Field Crops. Also be aware of potential harvest restrictions (usually 20 to 30 days) that can also be found on page 110 in 2009 Weed Control Guide for Field Crops. As always, if there is ever any doubt consult the herbicide label.

A proactive weed management program in alfalfa, as in all crops, is often the most effective means to keep your crop weed-free and help ensure maximum yield potential. If these weeds have become a problem in your alfalfa, be prepared to make fall or spring applications to dormant alfalfa to improve control and avoid yield losses or decreased quality in next season’s first cutting. 

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