In the age of herbicide resistance, integrated management is key

Date:11-24-2016

As the the Arkansas State Plant Board considers public input and works toward final recommendations for the registration and use of a new generation of herbicides, experts with the University of Arkansas System Division of Agriculture and other research institutions are looking to the future of row crop farming in the state.

Tom Barber, professor of weed science for the Crop, Soil and Environmental Science Department at the University of Arkansas System Division of Agriculture, said that while advancing seed and herbicide technologies were key to the industry’s future, they shouldn’t be looked at as the “alpha and omega” of future farming.

“From a ‘mode of action’ standpoint, there’s nothing immediate in the pipeline,” Barber said. “People think of the recent herbicide variants as ‘new,’ but this chemistry has been around for a long time.

“When we talk about dicamba, it is an average pigweed herbicide at best,” he said. “It is not as good as Roundup was on non-glyphosate-resistant Palmer amaranth.”

An uphill climb

Between the relative success of Monsanto’s Roundup Ready technology and a typically steep “uphill climb” in store for companies attempting to register new modes of action with the U.S. Environmental Protection Agency, the past decade saw a decline in innovation from herbicide manufacturers, said Bob Scott, professor of weed science for the Division of Agriculture.

“We’re behind the curve on new technologies,” Scott said. “There was a big down time, during the Roundup Ready years, where companies didn’t do a lot of work developing new herbicides, because there just didn’t seem to be any market share for them.”

“But in many of the companies, I think they’re restarting their discovery teams,” Barber said. “So hopefully we’ll find something the next four to five years.”

Innovation by farmers

Jason Norsworthy, professor of weed science and Elms Farming Chair for the Division of Agriculture, said much of the innovation in farming will likely come from growers themselves.

“We’re at a point today where economic returns are pretty minimal in the farming industry,” Norsworthy said. “I’m convinced that farmers today are some of the most innovative individuals out there.

“The big thing here is that herbicides are the foundation of what we do from a weed control standpoint,” he said. “But just like any foundation, they’re not the be-all-end-all of what we’re doing in weed control.”

Zero Tolerance

Norsworthy and Barber said they and other researchers had been focusing ongoing research, in part, on cultural practices, including the use of cover crops and “weed seed destruction.”

“In my opinion, this is going to revolutionize the way we control weeds in Arkansas,” Barber said.

By installing a grinding apparatus on a combine, growers can pulverize any Palmer amaranth or other unwanted seed during the post-season tillage phase of their operation.

“Any weeds that are left in the fields at harvest, potentially all of that seed could be destroyed, thus significantly reducing the weed seed bank over time,” Barber said.

Norsworthy warned that the danger of resistance is inherent in any single weed-management strategy.

Camouflaged as rice

“There’s barnyardgrass in rice in Asia that has evolved resistance to hand-weeding,” Norsworthy said. “How? After hundreds and hundreds of years of using hand weeding as the only means of removing barnyardgrass from rice, you now have the weeds that look identical to rice. So in the field, you can’t differentiate one from the other.

“It’s no different from what we’re dealing with today,” he said. “If we think we’re going to move forward with a single herbicide, and that it’s going to be simple from this point forward, we’re mistaken. There’s no way that’s a long-term solution. Simplicity isn’t going to be a long-term solution to weed management.”

Other cultural practices such as having a “zero tolerance” policy toward pigweed, can go a long way to move toward reducing its presence in the state.

“The idea is that you don’t let any pigweed go to seed,” he said. “Whether it’s in the field, on the turn row, in the ditch, in the equipment yard — if you see one, you pull it up, spray it with a non-selective herbicide, and don’t let them go to seed.

“The weakness in pigweed is that the seeds aren’t viable much past three or four years,” Barber said. “So if we can reduce the weed seed bank by removing all the plants that produce seed, we’ll start getting ahead of the pigweed population in the field. Zero Tolerance ties back into the harvest weed seed destruction, both of these are cultural methods to reduce the pigweed seedbank over time.”

Barber cautioned growers moving to quickly toward one technology or another in the short term.

“It seems like anymore, the market drives more decisions than the science does,” he said. “And maybe that’s the way it’s always been, I don’t know.

“I’ve heard we have enough seed in Arkansas to plant 70-80 percent of our soybeans in an Xtend variety — and this is brand new technology,” he said. “Our recommendation would be to move into this technology slowly, and figure out if these varieties are going to yield. But what the market is doing is pushing these beans on these growers, and I think a lot of them are scared that their neighbor’s going to drift on them, so they’re buying the Xtend beans for protection.

"So we could see a shift next year from currently a Roundup and Liberty soybean system to a 70-80 percent Xtend soybean system in one year, and that could be very problematic for other types of susceptible soybean varieties in the Delta, and would not be the wisest move for long term resistance management of pigweed," he said.