In-season weed management in alfalfa
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.
Although many people are still concerned about getting their corn and soybeans planted, the first alfalfa cutting is soon approaching. The cool, wet weather early this season kept many people from making herbicide applications to dormant alfalfa, leading to a greater incidence of winter annual weeds in their fields making postemergence in-season applications necessary. Winter and summer annual grass weeds can effectively be controlled with Poast or Select, however be aware of the harvest restrictions with these herbicides. Once alfalfa breaks dormancy and has appreciable new growth, most broadleaf herbicides can cause injury to alfalfa. When trying to determine whether to apply herbicides or not, remember in many cases the easiest and most economical solution to winter weed problems is the first cutting.
Summer annual weeds are beginning to emerge and become established at the first cutting. Control of these small weeds can be accomplished with herbicides such as Gramoxone Inteon at 1 pt/A, Pursuit at 4 oz/A, Velpar at 1 qt/A, Raptor at 5 oz/A when applied between cuttings. Be sure to make these between cutting applications before one to two inches of alfalfa growth occurs, usually within four to five days. Also be aware of use restrictions. For example, do not make sequential applications of Pursuit and Raptor within a 60-day period to avoid potential herbicide injury, and be aware of rotation restrictions if the alfalfa stand is nearing the end of its life. Herbicide rotation restrictions can be found on pages 146-149 in 2009 Weed Control Guide for Field Crops. The majority of herbicides also have a harvest restriction (usually 20 to 30 days), however a harvest restriction for an application made within four to five days after cutting shouldn’t delay the next cutting substantially. Harvest restrictions for herbicides in alfalfa can 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.