MDA shares weed control alternatives for dicamba tolerant soybeans

XtendiMax, Engenia, and Tavium are dicamba herbicides labeled for postemergence application on Xtend soybeans. Although these products are less volatile than older dicamba formulations, drift of dicamba vapor from treated fields resulted in damage to adjacent crops and landscape plants. To reduce the chance of injury, application cutoff dates and temperature restrictions were established.

In 2022, applications must be made by June 12 on fields south of Interstate Highway 94. For dicamba tolerant soybean fields north of Interstate Highway 94, the dicamba application cutoff date is June 30. In addition to location in the state, there is also a temperature restriction. Do Not make dicamba applications in dicamba-tolerant soybeans if the daily high temperature is or forecasted to be over 85°F.

Due to the cool, wet spring this year, there is concern that the application cutoff dates will pass before soybeans can be sprayed. If this happens, what options do soybean growers have? The options available depend on the crop growth stage. If the soybeans have not emerged, consider putting down a preemergence herbicide such as metribuzin (Derive, Dimetric, Metricor), linuron (Lorox), imazethapyr (Pursuit), chlorimuron (Classic), thifensulfuron (component in Harmony Extra, Resolve, Synchrony), cloransulam (FirstRate), pyroxasulfone (Zidua), dimethenamid (Outlook), or others to reduce late germinating weeds. Some preemergence herbicides, such as metolachlor, can be applied early postemergence if the crop has already emerged. The label specifies the crop stage restrictions. These herbicides will not control emerged weeds but will reduce late germinating species.

If soybeans have already emerged, the available options will depend on the herbicide tolerance of the planted soybeans. RR2 Xtend soybeans are tolerant to glyphosate as well as dicamba, so glyphosate can still be used to control many weed species. However, if glyphosate resistant weeds are present, they will not be controlled, so another herbicide will need to be added. If XtendFlex soybeans were planted, glyphosate or glufosinate (Liberty, Finale) can be utilized. Since glufosinate can antagonize glyphosate, do not tank-mix them. If both are to be applied, spray glyphosate first, followed by glufosinate a week later after the glyphosate has had time to be absorbed and translocated.

Several postemergence herbicides such as bentazon (Basagran), chlorimuron (Classic), fluthiacet (Anthem, Cadet), fomesafen (Reflex, Flexstar), lactofen (Cobra), and others are available for broadleaf weed control in non-herbicide-tolerant soybeans. When selecting herbicides to apply, match their activity to the weed species present. Consider the presence of herbicide resistant weeds when selecting herbicides. Effective postemergence grass control can be obtained with herbicides such as fluazifop Fusilade), fenoxaprop (Acclaim, Fusion), quizalofop (Assure, Targa), sethoxydim (Poast), and others with good crop safety. Herbicides with several sites-of-action are available including amino acid synthesis inhibitors, photosynthesis inhibitors, cell membrane disruptors, pigment inhibitors, and others.

There are numerous herbicide options available, so consider consulting a weed control guide such as, North Dakota Weed Control GuideSouth Dakota Pest Management  Guide, or  Herbicide Guide for Iowa Corn and Soybean Production. Be certain to use up-to-date information. (Use of sample commercial herbicide names in this article does not represent an endorsement.)

In addition to herbicides, growers can utilize mechanical weed control such as a rotary hoe. Interrow cultivation can also be used if the row spacing is wide enough for equipment.

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