Larry Steckel, a University of Tennessee Extension weed specialist in Jackson, likes to compare the growing problem of herbicide-resistant weeds to Americans’ health habits.
You’re going along overweight, smoking and drinking a bit too much beer. In the back of your mind, you know you should change your habits, but you won’t until a health issue, such as a heart attack, serves as a wake-up call.
Well, many growers—particularly those in the Midwest and South who grow Roundup Ready crops—are having a “pigweed heart attack,” to use Steckel’s words.
Some fields may never recover from that pigweed heart attack. But it should serve as a wake-up call to others, including growers of specialty crops, to change their habits and adopt a more herbicide-healthy lifestyle.
That includes scouting before and after herbicide applications; rotating modes of action; using tankmixes that contain different modes of action; using proper adjuvants, nozzle sizes and droplet sizes; rotating crops where applicable; and using mechanical cultivation if possible.
Steckel told his story at BASF and Bayer CropScience media conferences leading up to the recent Commodity Classic in Nashville.
Scattered pockets of glyphosate-resistant weeds have been confirmed in specialty crops throughout the nation.
They include rigid ryegrass in California’s Imperial Valley and northern Sacramento Valley; Italian ryegrass in Oregon filbert orchards; marestail and hairy fleabane in central California; and Palmer amaranth in a handful of Georgia vegetable fields and New Mexico pecan orchards.
But the resistance problem isn’t nearly as widespread as the millions of acres of infested corn, soybean and cotton ground where growers had adopted an herbicide program based almost exclusively on glyphosate.
In a few short years, water hemp in the Midwest and Palmer amaranth in the South have grown so resistant to glyphosate that many growers never harvest their crops. Instead, they take bush hogs or disks to them, Steckel says. Both weeds are members of the pigweed family.
He estimates that Palmer amaranth cost Tennessee growers of field crops $120 million in 2011 alone.
“If you’re doing a scorecard, we’re failing at trying to steward glyphosate,” Steckel says. “We’re running it right off a cliff in many of our areas.”
One of the linchpins of an integrated weed management program is scouting, both before and after herbicide application.
You need to scout initially to determine what weed species are present, he says Then choose the appropriate products based on the pest spectrum.
You also need to scout after the application to determine the extent of control. If you see a healthy weed next to a dead weed next to an injured one, that’s a sign that something’s wrong.
Leaving those healthy but treated weeds in the field is the worst thing you can do, Steckel says. You need to remove them immediately.
Growers in the South learned the hard way. They saw a few Palmer amaranth plants escape glyphosate treatments one season. The next year, the problem had spread throughout most of the field. And by year three, the field was unharvestable and you couldn’t see the crop for the weeds.