Herbicide-resistant weeds are not hard to spot.
“We have mares tail,” said farmer George Krom III of Indiana. “We have it right here. That’s a real bad weed for us.”
Farmers say it’s a growing problem, costing time, money and management.
“The biggest issue we have is now trying to manage resistant water hemp,” said Ken Ferrie, agronomist of Farm Journal. “It’s changed a lot of people’s programs across the board as far as back to the high dollar weed control programs itself.”
“Right now, somewhere in Illinois or the United States, there is a weed growing resistant to a herbicide that hasn’t even been discovered yet,” said Aaron Hager of Univeristy of Illinois Extension.
Hager is a University of Illinois Crop Science Professor and has been studying weeds for more than twenty years. Hagar said the list of resistant weeds is growing, and the problem is larger than glyphosate.
“Our most challenging topic related to resistance in our species in Illinois for example is water hemp,” said Hager. “The fact that it also has evolved a resistance to herbicides of literally five different classes of chemistry.”
“Some of these weeds have 200,000 seed heads and they spread rapidly once resistant,” said Bill Bauer, agronomist.
So how should farmers control it? Hagar said it may not be just a chemical solution. It depends on how growers steward it.
“There is no one sustainable herbicide solution that will run indefinitely,” said Hager.
He believes even if farmers switch to a new commercialized product, it will be widely used and the cycle may start all over again.
“If you look at what the industry may commercialize in terms of new active ingredients say in the next five years or so; there doesn’t appear to be any,” said Hager. “We are rapidly depleting what options we do have now every time that resistance continues to increase.”
That’s why he feels the solution needs to target the most vulnerable stage of the plant. That’s not after the seed has germinated and the plant has emerged, but the seed itself.
“A lot of studies have actually shown that somewhere between seven to ten years, much of the viability in the water hemp seed would be lost. If there are practices we can do again, whether chemical, manual or whatever they may be to hinder water hemp seed from being produced in the field for three years, four years in a row, we can start to see these numbers really go down,” says Hager.
He says ultimately the solution may be chemical, mechanical or manual or even a combination. For example, that could be alternating planting dates.
"[That could be] By doing something as simple as delaying spring planting by a few days, who knows how many seeds you may have exhausted from that seed bank,” said Hager.
That could also be going back to old practices like walking beans or cultiving. Ron Haas, an Illinois farmer, kept his cultivator but hopes he doesn’t have to use it.
“I hope I don’t have to put that to use, but we haven’t gotten rid of it yet,” said Haas.
Resistant weeds, once rare, now common. That’s as farmers and industry leaders move forward to control it.
“We’re going to change our chemical program a little and do our best,” said Krom III.
Hager says he’s mostly asked about water hemp, rag weed, morning glory, palmer amaranth and mares tail. Those are all weeds that weren’t always on farmer’s minds. Twenty years ago, those conversations were all about thistles and cockaburrs.
