2,4-D is coming back. What many might consider a “dinosaur” may be the best solution for growers fighting weed resistance today, said Dean Riechers, University of Illinois associate professor of weed physiology.

“Farmers can’t imagine going back to 2,4-D or other auxin herbicides,” Riechers said. “But herbicide resistance is bad enough that companies are willing to bring it back. That illustrates how severe this problem is.”

In a recently published article in Weed Science, Riechers and his team of research colleagues suggest that tank-mixing auxinic herbicides with glyphosate may be the best short-term option available to farmers interested in broad-spectrum, postemergence weed control.

“Resistance has become a big problem,” Riechers said. “In 1997, researchers predicted that glyphosate resistance would not be a big issue in Roundup Ready crops. For the most part, they were right. But they underestimated a few weed species and resistance mechanisms.”

Since the 1950s, 29 auxin-resistant weed species have been discovered worldwide. In comparison, 21 glyphosate-resistant weed species have been discovered since 1996 when Roundup Ready soybeans were commercialized.

“And interestingly enough, two of the most problematic weeds in Roundup Ready soybeans and cotton — common waterhemp and Palmer amaranth — are not yet on the list of auxin-resistant weeds, Riechers said.

Ideally, chemical companies would come up with a new herbicide to fight these resistant weeds. But new herbicide development is expensive and time-consuming. Riechers said he does not know of any new compounds on the horizon.

“If we don’t find completely novel and new herbicides, our next best bet is to mix glyphosate and another herbicide with relatively minor resistance problems,” Riechers said.

“Auxin resistance is not considered a huge problem in the United States, particularly in corn, soybeans and cotton. It has only occurred in isolated incidences.”

Why have the auxinic herbicides escaped the resistance problems of the more modern herbicides used today?