Glyphosate is a special chemical, with the combination of low mammalian toxicity, favorable environmental profile, and broad spectrum control imparting a uniqueness to this herbicide. However, it was the development of glyphosate-tolerant crops that resulted in wide-scale adoption of glyphosate as a foundational herbicide over hundreds of millions of hectares in theAmericas. For several years in the late 1990s, weed control was highly effective, economical, and simple. However, with this massive selection pressure, the evolution of weeds no longer controlled by glyphosate was inevitable, and this has occurred in numerous locations in several genera. The major agronomic examples of these weeds include Conyza canadensis, a winter annual that is problematic in no-tillage production systems, and Amaranthus palmeri, a tremendously competitive summer annual that is a growing problem in the southern United States. Incomplete control from glyphosate has also been reported on species from the Sorghum, Ambrosia, Conyza, and Amaranthus genus. This talk introduces the important topic of herbicide resistance in today's American agriculture. Issues discussed include comprehensive surveys of the occurence of herbicide resistance, how farmers are responding to this change, and future opportunities and responses to manage this problem.

Glyphosate is not the herbicide it used to be: A North American perspective

246th National Meeting (2013)

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