Control volunteer soybean in corn
ST. PAUL -- Volunteer soybean in corn is a fairly recent phenomenon caused by widespread use of the glyphosate-resistant technology in corn and soybean. My colleagues and I at University of Minnesota Extension have received several recent inquiries about cost-effective control procedures.
Overall, soybean size at time of herbicide application will determine the degree of control with small, V2 to V3 (second to third trifoliolate) soybeans more effectively controlled than soybeans in the V4 to V6 (fourth to sixth trifoliolate, after which plants will begin flowering). Application to small plants is especially important if you want to keep your herbicide application rates low.
Due to its low cost, several growers have been interested in using 2,4-D to control volunteer soybean; however, based on work done at North Dakota State University, soybeans are not as sensitive to 2,4-D as they are to the other plant growth regulator herbicides dicamba or clopyralid.
Another low-cost alternative being discussed by producers is atrazine, which would be a better option than 2,4-D due to its crop safety and level of soybean control, but it's less effective as soybeans enter the V4 to V6 growth stage.
Plant-growth regulator herbicides such as Hornet contain clopyralid and should provide effective control to smaller soybeans. Products that contain dicamba, such as Status, Distinct and numerous generics, should provide effective control over a wider range of volunteer soybean crop sizes.
You can find a summary of an NDSU study titled "Control of Volunteer Roundup Ready Crops" at www.ag.ndsu.edu/weeds/weed-control-guides/nd-weed-control-guide-1 and click on "Weed Control Ratings." For more information for corn growers from University of Minnesota Extension, visit www.extension.umn.edu/Corn.University of Minnesota weed control recommendations may be found at www.extension.umn.edu/go/1035.
Jeff Gunsolus is a weed scientist with University of Minnesota Extension.