Glyphosate Tolerance vs. Glyphosate Resistance (June 25, 2014)

We hear a lot about herbicide resistance of weeds to Glyphosate these days and it is a serious problem. It is important to keep in mind, however, that Glyphosate does not control all weed species and when weeds are not controlled it is often a case of “weed tolerance” rather than “weed resistance”.

Weed tolerance is when a weed species is not controlled by Glyphosate and never has been. Weed resistance is when a weed species was controlled by Glyphosate but no longer is. This occurs because of changes that have naturally occurred in the field and not because of changes that were created by the herbicide.

Some weed species that are “tolerant” to Glyphosate and have never been well controlled by it are Sweet Clover, Malva and Annual Bluegrass. Weeds that are only partially controlled by Glyphosate are Lambsquarters, tumble pigweed, prostrate knotweed, and goosefoot. In general, control of grasses is more inconsistent than control of broadleaf weeds.

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