Growers with winterkilled alfalfa in older stands can remove it with herbicides and/or aggressive tillage, says Mark Renz, University of Wisconsin Extension weed scientist. (See “Winterkill Claims Alfalfa, Other Forages In Upper Midwest.”)
“If using herbicides, remember to read the label of the products used, as plant-back restrictions can vary between products,” he warns.
Applying herbicide before tillage “greatly improves chances of alfalfa mortality. For no-till fields, spring herbicide application can provide good to great removal depending on the year,” Renz says. When alfalfa plants are stressed, as they are this year, they often resprout and require control in the following crop.
Most labels recommend at least 4” of alfalfa regrowth to maximize control. The most popular active ingredients in herbicides used to control the legume include glyphosate, 2,4-D, and/or dicamba. Glyphosate has no plant-back restrictions for other crops, but 2,4-D and dicamba do.
“The restriction varies depending on the crop, rate and product, so read the label carefully,” he says. “In a typical year, the restriction for 2,4-D (seven-14 days for corn) and dicamba (zero-30 days for corn) can be met easily prior to planting corn without a yield hit. This year, however, an application of one of these products may result in a one- to four-week delay in planting.”
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Growers planning to harvest first-crop conventional alfalfa before terminating the stand should apply glyphosate 36 hours or longer before harvesting. Up to 1.5 lbs acid equivalent (ae) per acre is registered for this type of application. This will allow for hay harvest and improve effectiveness of removal. “I am not aware of any other herbicides that can be used in this fashion,” he says.
Or growers can harvest the hay, let the alfalfa regrow and then apply herbicide to eliminate the stand. This adds at least two weeks time before planting and plant-back restrictions would need to be followed, Renz says.
To control volunteer alfalfa, consider using glyphosate on Roundup Ready crops unless you’re removing Roundup Ready alfalfa. Other products containing dicamba or clopyralid are effective in corn. “I am not aware of effective non-glyphosate options in soybeans. Make applications in a timely fashion, as I expect significant yield loss could be seen from volunteer alfalfa in fields,” Renz advises.
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