A study by Washington State University scientist Charles Benbrook on the impacts of three genetically engineered herbicide-resistant crops -- cotton, soybeans and corn -- on herbicide usage found the emergence and spread of resistant weeds is strongly linked to the increased use of glyphosphate pesticides.
Marketed as Roundup and under other trade names, glyphosate is a broad-spectrum systemic herbicide used to kill weeds and is extensively used with crops that have been genetically modified to be herbicide resistant.
However, the study found, use of glyphosate has had to be increased each year with shifts in weed communities and the emergency of more herbicide-resistant varieties.
"Resistant weeds have become a major problem for many farmers reliant on GE crops, and are now driving up the volume of herbicide needed each year by about 25 percent," Benbrook said in a university release Tuesday.
While herbicide-tolerant crops worked extremely well in the first few years of use, Benbrook said, over-reliance may have led to the creation of "superweeds" that force farmers to increase herbicide application rates and spray more often.