If you've been regularly using an ALS-inhibitor herbicide such as Accent or Beacon on corn and were getting shattercane control — and now you're not — you could have ALS resistance. That's the observation of University of Nebraska weed scientist Alex Martin.
ALS-resistant shattercane has been confirmed in Nebraska, Kansas, Illinois and Ohio.
Nebraska weed specialists first found shattercane resistance to Beacon in 1996. Subsequent testing showed that plants resistant to Beacon were also resistant to Accent and Pursuit. But those plants remained susceptible to labeled non-ALS herbicides.
To date, suspected shattercane resistance to ALS herbicides has been reported in Thayer, Buffalo and Webster counties in Nebraska. One common denominator of these fields is an annual application of an ALS-inhibiting herbicide such as Beacon, Accent or Pursuit. Most fields have been in continuous corn and had Beacon applied at least four years. Pursuit was applied to fields rotated to soybeans.
Ohio State University weed scientist Jeff Stachler reports that recent greenhouse studies have confirmed ALS-resistant shattercane in Fairfield County, OH. It was resistant to a 2x rate of Accent, Beacon and Pursuit.
Stachler says the affected field had been planted to continuous corn, with Accent and/or Beacon applied every year since 1990, except one.
“There may be additional shattercane populations in Ohio that are ALS-resistant,” Stachler notes.
“Few corn herbicide options are available for control of shattercane suspected to be ALS-resistant,” he points out. “For corn fields with ALS-resistant shattercane, Roundup Ready or Liberty-Link corn are the alternatives.”
Nebraska specialists recommend that shattercane can be controlled, but not suppressed, with a pre-emerge application of Axiom, Balance Pro, Balance Pro + Dual II Magnum, TopNotch or Degree, or Eradicane or Epic, Stachler says. On Roundup Ready or Liberty Link corn, post applications of glyphosate products or Liberty also will be necessary.
“Glyphosate products will provide more consistent control as compared to Liberty,” says Stachler. “This is especially true where a second postemergence application is not planned.
“Two postemergence applications of glyphosate products or Liberty is another control strategy. That could provide the most effective control.”
Stachler reports that where ALS-resistant shattercane and johnsongrass grow near each other, they can cross-pollinate. “There is concern about ALS-resistant johnsongrass. Only glyphosate products will control ALS-resistant johnsongrass.”
In a corn-soybean rotation, Roundup on Roundup Ready soybeans is dynamite for controlling shattercane, says Nebraska's Martin. “Pre-emergence products such as Treflan or Prowl also are effective in soybeans. Other postemergence soybean herbicides are Assure II, Fusilade DX, Poast Plus, Fusion and Select.”
The best way to manage herbicide resistance, say Nebraska specialists, is to detect it early. Keep resistance from spreading to non-infested fields by cleaning farm machinery before moving it to another field.
Switch to herbicides with different modes of action to prevent resistance.