By Mary Hightower, University of Arkansas System Division of Agriculture
Finding ways to halt the “resistance treadmill” was a key message from weed scientists on February 28 at Pigposium III, a daylong event hosted by the University of Arkansas System Division of Agriculture focused on herbicide resistant Palmer amaranth.
About 300 attendees from the agriculture industry – including farmers, extension agents and consultants – heard weed scientists from four states describe research and strategies for managing weeds that have developed resistance to the most-used herbicides.
Jason Norsworthy, weed scientist with the University of Arkansas System Division of Agriculture, noted that it’s been 12 years since the existence of glyphosate-resistant Palmer amaranth, better known as pigweed, was first confirmed in Georgia.
A year later, in 2006, glyphosate-resistant pigweed was confirmed in Arkansas and Tennessee.
In just over a decade, “31 states now have glyphosate-resistant Palmer amaranth,” he said. “The world’s greatest herbicide is no longer effective against pigweed.”
In defining what he called the resistance treadmill, Bob Scott, weed scientist for the University of Arkansas System Division of Agriculture, said, “We’re taking one herbicide and replacing it with another, and taking another herbicide and replacing it with another, and taking another herbicide and replacing it with another. Today, the goal is to stop doing this.
“If we follow our resistance pattern, we’re just going to add dicamba to the growing list of resistance that we have,” he said. “We’ve proved this in a laboratory study.”
Scott said ALS resistance perpetuated glyphosate resistance, and glyphosate resistance perpetuated PPO resistance. He asked, “What will PPO resistance perpetuate?”
This pattern, this treadmill, will eventually lead the industry to “multiple stacked resistance,” Scott said. “I’m a weed scientist and that scares me. Stacked resistance is a game changer.”
Scott’s comments were echoed by fellow Division of Agriculture Weed Scientist Tom Barber, “If you continue to rely just on PPOs, you’ll shift the population in that field to PPO resistance.”
Norsworthy, in talking about the future of herbicide use said, it’s “just a matter of time before we have a six-way stack” in herbicide resistance.
He quoted Eric Maupin, a Tennessee farmer who is a board member of the American Soybean Association, saying “going into 2016, I have one post-emergence option for pigweed, and if I were to lose that option, I wouldn’t be farming soybean.”
“That,” Norsworthy said, “is a very sobering statement.”
Norsworthy spoke about several options being tested, including narrow windrow burning and seed destructors.
“Narrow windrow burning was quite effective, with complete control of all weed seed,” he said. “We killed every weed seed in that row.
Another option were seed destructors that used mills to crush seed. “This gets me excited,” added Norsworthy. “It lessens the seed going back into the soil.”
Larry Steckel, a Tennessee Extension weed scientist, talked about the use of cover crops.
He said he is often asked if cover crops are effective in managing resistant weeds. “Yes,” he said, with a pause. “How much time to I have left?”
Steckel said cover crops are highly effective, but not a silver bullet. But using them would likely reduce by one, the number of herbicide applications needed by growers.
Michael Popp, an agricultural economist with the University of Arkansas System Division of Agriculture, walked the audience through Palmer amaranth manager, or PAM, a PC-based program that enables growers to develop their own strategy in managing pigweed.
Kevin Bradley, a Missouri Extension weed scientist, discussed the issues with dicamba in his state. He said that farmers with crops injured by dicamba didn’t want to turn other farmers in, so the reported damage might not have been the whole story.
Bradley said the state’s legislature was pondering a bill to fine growers $1,000 an acre for illegal applications.
Pecan, peach, white and red oaks proved to be very sensitive to dicamba, and Bradley said he expected that “homeowners, with half their trees defoliated, will figure this out.”
Ples Spradley, Extension pesticide assessment coordinator for the University of Arkansas System Division of Agriculture announced where growers can find an online course that’s required for use of Enlist Duo and Engenia herbicides in Arkansas.
Jason Davis, application technologist, emphasized that droplet and nozzle size matter when applying herbicides. Producers need to find the right balance between trying to ensure the herbicide goes just where the applicator needs it, and a droplet size that will ensure the herbicide’s efficacy.
Pigposium wound up with three producers sharing their experience with various weed management methods. Harry Stephens of Helena talked about his successful use of narrow windrow burning and how a relatively small investment paid large dividends.
Dane Coomer of Piggott, told the audience about his experience with Zero Tolerance in cotton.
“It’s a mindset and it’s a goal,” he said. “If you see one on your farm, you pull it.”
Coomer said he uses chopping crews to eliminate remaining weeds by hand. “You may only see a half dozen, but there will be ones you don’t see. That crew will get the ones you don’t see too.”
Adam Chappell, a producer at Cotton Plant, talked about successful use of cover crops, telling the audience he’d been using the same beds since 2010. He pointed to a list of weed management tactics in his presentation, saying “prayer is the only thing up there that’s free.”
Using cover crops, “I’m doing the same thing with half the money,” Chappell said.
Norsworthy left his audience with this message. “Do something different next year,” he urged. “Glyphosate was the world’s greatest herbicide. And I said ‘was.’ If we had only done something different in the late 90s and early 2000s, we’d still have the greatest herbicide today.”