Abstract
Genetically engineered (GE) herbicide-resistant crops have been widely adopted by farmers in the United States and other countries around the world, and these crops have caused significant changes in herbicide use patterns. GE crops have been blamed for increased problems with herbicide-resistant weeds (colloquially called by the misnomer “superweeds”); however, there has been no rigorous analysis of herbicide use or herbicide-resistant weed evolution to quantify the impact of GE crops on herbicide resistance. Here, I analyze data from the International Survey of Herbicide Resistant Weeds and the USDA and demonstrate that adoption of GE corn varieties did not reduce herbicide diversity, and therefore likely did not increase selection pressure for herbicide-resistant weeds in that crop. Adoption of GE herbicide-resistant varieties substantially reduced herbicide diversity in cotton and soybean. Increased glyphosate use in cotton and soybean largely displaced herbicides that are more likely to select for herbicide-resistant weeds, which at least partially mitigated the impact of reduced herbicide diversity. The overall rate of newly confirmed herbicide-resistant weed species to all herbicide sites of action (SOAs) has slowed in the United States since 2005. Although the number of glyphosate-resistant weeds has increased since 1998, the evolution of new glyphosate-resistant weed species as a function of area sprayed has remained relatively low compared with several other commonly used herbicide SOAs.
Highlights
The earliest known report of evolved herbicide resistance in weeds dates back to 1957 (Hilton 1957)
Because there was no “control” group in the adoption of Genetically engineered (GE) crops, it is important to compare the observed trends in herbicide use from GE crops with broader trends observed in non-GE crops
If the herbicide use trends observed in GE crops are substantially different from non-GE crop trends, there is a greater likelihood that those trends are at least partially attributable to GE crop adoption
Summary
The earliest known report of evolved herbicide resistance in weeds dates back to 1957 (Hilton 1957). The objective of this analysis was to identify trends in herbicide use and evolution of herbicideresistant weeds in the United States, especially as they relate to adoption of GE herbicide-resistant crop varieties. Adoption of glyphosate-resistant cotton and soybean varieties in the United States was rapid, reaching over 50% of total crop area within 6 yr of commercial introduction.
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