Weed control of winter annuals should be on the mind of producers as we move into March. The minimum temperature range for control of winter annuals including marestail (horseweed) and annual ryegrass is 50o F.
Herbicide rate can compensate some at lower temps but 40o F should be the lower cutoff. Application timing for maximum potential control is when marestail is in the rosette stage of growth. Allow enough time between burndown and planting to insure crop safety and to evaluate control.
Avoid planting into emerged marestail, especially with soybeans since in season control is very limited.
Targeting marestail this spring the products that provide good POST control are programs containing growth regulating herbicides, dicamba, or 2,4-D or a package mix of the two as the base plus glyphosate. Another product that can be can provide marestail control is suflufenacil (Sharpen/Verdict). Other contact burndown tankmix choices include paraquat (Gramoxone) and glufosinate (if you are NOT planting Liberty Link soybeans).
Residual herbicides containing ALS mode of action (Group 2) can provide residual control of ALS-sensitive populations. Herbicides containing residual activity including growth regulating herbicides have plant back restrictions that must be followed or crop injury will occur. Read and follow all label instructions.
Two links that I recommend you read for specific management of marestail are Take Action publication “Management of Herbicide Resistant Horseweed (Marestail) in soybeans” and Arkansas-crops article “Winter annual burndown. Will the weather cooperate?”
Both can be found at their respective links:
