Herbicide-Resistant Weed Found In Ohio County

AgAnswers / Purdue 6mar01

Ohio State University greenhouse studies recently confirmed the resistance of one shattercane population to aceto-lactase synthase (ALS)-inhibitor herbicides.

Shattercane in Fairfield County survived after researchers applied double rates of Accent, Beacon and Pursuit herbicides to weed samples.

"It might not be a big problem for most farmers, but shattercane resistance to ALS herbicides is a big problem for those farmers who have it," says Jeff Stachler, OSU Extension associate.

"We really don't have many other options for controlling it. That's the sad part about it."

More terrifying, though, is that shattercane may spread its resistance because it can cross-pollinate with johnsongrass, a real troublemaker that farmers dread, Stachler says.

"Ohio is a place where this can occur, because in other states with ALS-resistant shattercane, like Kansas and Nebraska, both shattercane and johnsongrass usually don't coexist in the same field, and thus chances for cross-pollination are greatly reduced," Stachler says.

OSU's list of other ALS-inhibitor resistant weeds are common ragweed, giant ragweed, marestail (horseweed), common cocklebur, Powell amaranth and waterhemp.

The shattercane case is a classic example of why weeds become resistant to herbicides, Stachler says. "The field had been planted to corn and had Accent and/or Beacon herbicides, which have the same mode of action, applied in all but one year since 1990. Farmers who use herbicides without changing the mode of action every few years risk having weeds develop resistance."

ALS-inhibitors' mode of action kills weeds by interfering with an enzyme, cutting off some of the weed's amino acid production. Annually switching to products with different modes of action maintain weeds' biological diversity and their susceptibility to the original products.

For farmers with ALS-resistant shattercane, there are no complete shattercane control options if planting normal hybrids, Stachler says.

"Recommendations from the University of Nebraska, where shattercane abounds, suggest that Axiom, Balance, Balance plus Dual II Magnum, Topnotch, or Degree, Eradicane, or Epic herbicides applied pre-emergence can suppress shattercane, but will not control it."

Herbicide-resistant shattercane also is present in Indiana, says Case Medlin, a Purdue University Extension weed specialist.

"We ran a couple of tests and we're showing the same thing" as Ohio, Medlin says. Research is ongoing, he adds.

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