Johnsongrass, one of the world’s most troublesome weeds, has become resistant to the herbicide glyphosate (Roundup) at sites in Arkansas and Mississippi. Johnsongrass is the latest in a string of resistant weeds that calls into question the widespread use of genetically engineered (GE) herbicide-tolerant crops. This year, U.S. farmers will apply Roundup, produced by Monsanto, to more than 100 million acres of soybeans, corn, and cotton engineered to tolerate the herbicide. These and other GE crops were sold with the promise of decreased pesticide use, but the overuse of any one herbicide almost inevitably leads to resistant weeds like the newly discovered johnsongrass.
