Transgenic crops and increasingly resistant weeds create new problems for growers and consumers
By Summit Voice
SUMMIT COUNTY — The use of herbicides associated with the cultivation three key herbicide-tolerant crops of has skyrocketed, increasing by 25 percent annually, according to a new study from Washington State University that analyzed trends in production of cotton, soybeans and corn.
The findings, described as counterintuitive by Washington State University research professor Charles Benbrook, are based on public data from the U.S. Department of Agriculture’s National Agriculture Statistics Service.
The annual increase in the herbicides required to deal with tougher-to-control weeds on cropland planted to GE cultivars has grown from 1.5 million pounds in 1999 to about 90 million pounds in 2011.
“Resistant weeds have become a major problem for many farmers reliant on GE crops, and they are now driving up the volume of herbicide needed each year by about 25 percent,” Benbrook said.
The upward trend of herbicide use is strongly correlated with the emergence and spread of weeds that have developed a resistance to glyphosate-based herbicides such as Roundup.
About 95 percent of soybean and cotton acres, and more than 85 percent of corn, are planted to varieties genetically modified to be herbicide resistant. Herbicide-tolerant crops worked extremely well in the first few years of use, Benbrook’s analysis shows.
During the first six years of commercial use (1996-2001), HT and Bt crops reduced pesticide use by 31 million pounds, or by about 2 percent, compared to what it likely would have been in the absence of genetically engineered crops.
But over-reliance may have led to shifts in weed communities and the spread of resistant weeds that force farmers to increase herbicide application rates (especially glyphosate), spray more often and add new herbicides that work through an alternate mode of action into their spray programs.
Today’s major genetically engineered crops have increased overall pesticide use by 404 million pounds from 1996 through 2011 (527 million pound increase in herbicides, minus the 123 million pound decrease in insecticides). Overall pesticide use in 2011 was about 20 percent higher on each acre planted to a GE crop, compared to pesticide use on acres not planted to GE crops.
There are now two-dozen weeds resistant to glyphosate, the major herbicide used on HT crops, and many of these are spreading rapidly. Millions of acres are infested with more than one glyphosate-resistant weed. The presence of resistant weeds drives up herbicide use by 25 percent to 50 percent, and increases farmer-weed control costs by at least as much.