Because of the resistant marestail population, our recommendation now is to mix a product that will have activity on marestail whenever glyphosate (roundup) is used. We do not know how extensive this resistant weed is. Forsoybean,2,4-D has excellent activity on marestail, as does first rate. For corn, 2,4-D or clarity (which can be found in several products) provides excellent control.

This also causes us to rethink our weed management strategy to reduce the chances of other weeds becoming resistant to glyphosate. There are several midwest states reporting not only marestail, but other weeds that have become resistant to glyphosate. Some of these weeds include: palmer amaranth andcommon ragweed. Other weeds are being investigated for possible resistance, including: common waterhemp andcommon lambsquarter.

One factor seems to be common when reports of resistance appear. And that is that a roundup ready crop has been grown for several years in succession. To avoid or delay resistance, follow approved management techniques to reduce opportunities for resistance to occur, including: tank mixing herbicides, using different modes of action, using full rates, etc.