The evolution of herbicide resistant weeds in Iowa: description, implications, and solutions

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Proceedings of the Integrated Crop Management Conference

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Micheal D. K. Owen
Iowa State University
conference paper description
There has been concern about the evolution of glyphosate resistance in some Iowa weeds for many years although the field-wide existence of any problems has not been previously reported. It is important to recognize that in reality, common waterhemp (Amaranthus rudis*) with resistance to glyphosate was reported in fields near Everly and Badger, Iowa as early as 1998 (Zelaya and Owen 2002). However, the likelihood of weeds evolving resistance to herbicides pre-dates glyphosate-resistant weed biotypes by five decades (Harper 1956). The first identification of herbicide resistant weed biotypes pre-dates glyphosate-resistance by four decades (Ryan 1970) and currently there 19 herbicide mechanisms of action to which weeds have evolved resistance which compromise 334 weed biotypes from 190 weed species and infest an area that is impossible to estimate (Heap 2009). To date, 16 weed species have evolved resistance to glyphosate. All of these incidents of evolved herbicide resistance have one thing in common; the mismanagement of herbicide use. This paper will describe the current herbicide resistant weed situation for Iowa in general terms, address the implications of herbicide resistant weeds and suggest solutions to the problems.