A survey featured in the most recent issue of the journal Weed Technology shows that glyphosate-resistant weeds have begun to change the weed management practices used by growers.
Researchers at Kansas State University surveyed crop consultants in the fall of 2012 about weed management in western Kansas—a region where glyphosate-resistant kochia is on the rise. Kochia is found in crop fields, rangelands, and pastures throughout the Great Plains, including the western United States and Canada.
Glyphosate-resistant kochia was first discovered in Kansas in 2007. The survey showed that in the five years that followed, the percentage of fields infested by kochia rose from 47 percent to 70 percent. Survey respondents estimated that by 2012, one third of cropland in western Kansas was infested by glyphosate-resistant kochia.
During the same five-year period, growers increased their glyphosate use rates by 52 percent. They also increased the frequency of their glyphosate applications by 45 percent.
Though growers were using more glyphosate, the survey showed they also had diversified their weed management practices.
“In 2007 when the first glyphosate-resistant kochia was discovered, nearly half of Kansas fields received glyphosate-only weed control treatments,” said Phillip Stahlman, a Kansas State University weed scientist who co-authored the Weed Technology article. “By 2012, only 15 percent of fields received glyphosate alone.”
Survey respondents reported that tillage was proving to be the most consistently effective practice for managing glyphosate-resistant kochia.
Full text of the article, “Consultant’s Perspective on the Evolution and Management of Glyphosate-resistant Kochia (Kochia scoparia) in Western Kansas” Weed Technology, Vol. 29, Issue 2, April-June 2015, is now available.