Researchers at Kansas State University have found pigweed that tolerates dicamba and 2,4-D, two herbicides that are often used to combat the invasive weed. Pigweed, or Palmer amaranth, is difficult for farmers to control, growing up to 10 feet tall and capable of producing 1 million seeds per plant.
The emergence of “super weeds” that shrug off herbicides is an increasingly widespread problem in U.S. agriculture. Growers in the South have embraced GMO soybean and cotton varieties that tolerate dicamba because it is a newcomer to weed control in row crops, although the chemical has been used on farms for decades. The same can be said for 2,4-D.
“This is the first confirmed case of resistance to dicamba in Palmer amaranth, further magnifying the challenge to manage this weed in conservation tillage systems,” said Kansas State weed specialist Dallas Peterson. The weeds may be resistant to a range of other weedkillers as well, he said.
The resistant pigweed plants were found in a conservation tillage test site, in use for 45 years, where sorghum and soybeans were grown. “These types of mono-cropping systems are the perfect scenario to develop herbicide resistance but were established…prior to the time when herbicide resistance was much of a concern. This example further demonstrates the importance of a diversified crop rotation and weed control program utilizing multiple effective herbicide sites of action through time.”