Annual weed control in alfalfa: In-season 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.
Winter annual weeds can be problematic and reduce forage quality and yield in alfalfa during the spring of the year. The best method for weed management is good stand establishment and to control weeds in the fall or spring with herbicide applications to dormant alfalfa. Several herbicides are labeled for control of grass weeds, broadleaf weeds, or both when applied to dormant alfalfa. However, if you were not able to control your weeds during the fall or spring, postemergence in-season applications may be necessary. Once alfalfa breaks dormancy and has appreciable new growth, most broadleaf herbicides can cause injury to alfalfa. Grass herbicides such as Poast and Select can be used effectively to control many winter or summer annual grass weeds, however be aware of the various harvest restrictions with these herbicides.
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. The first cutting will remove the weeds with the alfalfa, and a weed management plan can be established with fall or spring applied herbicides to dormant alfalfa. Herbicide rates and recommendations can be found on pages 98 to 108 in 2008 Weed Control Guide for Field Crops.
In some cases weeds may emerge or continue to grow after the initial cutting, primarily summer annual weeds. Many small weeds can be controlled 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 the various herbicides. 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 141-143 in 2008 Weed Control Guide for Field Crops.
Most 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 several herbicides can be found on page 107 in 2008 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.