Recommendations for removing established legume stands without tillage

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.  

Growers have the option of using tillage and/or herbicides to remove a forage stand. If they choose to use herbicides, the ideal time to kill an established legume stands is in the fall. When removing a clover cover crop or an old alfalfa sod, the most effective and consistent approach to killing these forages is similar. The field should be mowed in late August or very early September in central and Lower Michigan or mid-August in northern Michigan. Following cutting, allow the plants to re-grow for four weeks before the herbicide application. At the time of application, the plant canopy should be at least six inches in height.

MSU trials have shown that a properly-timed fall application of glyphosate should be adequate at killing the weed and legume species commonly found in an old alfalfa or clover sod. Glyphosate at the minimum rate of 0.75 lb a.e./A is recommended for effective results (see Table 1 for glyphosate products and use rates). Always add ammonium sulfate (AMS) to the spray solution at 17 lb/100 gal. Farmers may choose to add a growth regulator herbicide, like 2,4-D ester or dicamba, to the glyphosate for insurance of adequate control of broadleaf perennial weeds. This practice is fairly inexpensive and may be beneficial under certain conditions such as applications made under less than ideal conditions. However, if a growth regulator is added to the tank mix, do not reduce the glyphosate rate as this could result in lost glyphosate efficacy due to herbicide antagonism.

For the past few years, MSU has studied chemical methods for the removal of glyphosate resistant alfalfa. Although glyphosate resistant alfalfa has been available for only a couple years, it is important that growers know how to remove it when it becomes necessary. Our results have shown that applications of 2,4-D (at 32 fl.oz./A), dicamba (at 32 fl.oz./A) or 2,4-D + dicamba (at 16 fl.oz./A + 16 fl.oz./A) in early fall or in the spring were more effective at removing old alfalfa stands than fall tillage alone. It is also critical that the plant canopy be at least six inches tall and actively growing at the time of application.

All removal applications should be targeted when the daytime high air temperatures are at least 60°F, when there is adequate soil moisture and preferably during sunny weather. Application should be made when the leaves are dry, the wind is calm and there is no risk of rainfall for several hours. The plants should be green, actively growing and not showing symptoms of frost injury.


Once removed, the logical rotation crop to following either an old alfalfa or clover sod is corn, since corn would benefit from nitrogen, produced by the legume. The amount of nitrogen available will depend upon the density of the legume stand at the time of removal
.

Table 1. Equivalent product rates for different glyphosate formulations at the recommended minimum application rate (0.75 lb a.e./A) for removing an established legume stand in the fall.

Product

Acid equivalent (a.e)

Rate per acre

Roundup WeatherMax / OriginalMax

4.5 lb a.e per gallon

22 fl. oz.

Touchdown Total

4.17 lb a.e per gallon

24 fl. oz.

Glyphomax XRT / Durango

4.0 lb a.e per gallon

24 fl. oz.

Various glyphosate products a

3.0 lb a.e per gallon

32 fl. oz.

(a.e) Refer to Table 10 in E-434, Weed Control Guide for Field Crops
Consult product label for the rate and type of surfactant needed. AMS should be included at 17 lb/ 100 gal to improve glyphosate performance.

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