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Check Mode of Action Before Spraying
As more weeds become resistant to a popular class of herbicides known as ALS inhibitors, researchers say the herbicide that worked for you last year may not be the best choice to use this year.
Growers should know their herbicide chemistry and avoid continuous use of the same mode of action, advises George Kapusta, weed specialist with Southern Illinois University.
"If you're using ALS inhibitors like Beacon in corn and Hannony Extra in wheat, then you should probably use a non-ALS inhibitor herbicide in soybeans," says Jim Martin of the University of Kentucky.
Researchers like Kapusta and Marhn are recommending herbicide rotation to minimize the spread of ALS-resistant weeds.
"We can trace our current problems with ALS-resistant waterhemp here in Illinois to the continuous use of ALS inhibitor herbicides like Pursuit and Classic in soybeans," says Kapusta.
ALS inhibitor herbicides for corn include Accent, Battalion, Basis, Beacon, Broadstrike, Exceed, and Permit. ALS inhibitor herbicides for soybeans include Classic, Pinnacle, Pursuit, Scepter, and Synchrony STS. Harmony Extra is a popular ALS inhibitor herbicide for wheat. All control weeds by inhibiting the ALS (acetolactate synthase) enzyme.
Resistance to these herbicides can develop when they are used year after year. Currently, ALS-resistant waterhemp is a problem in many parts of the Corn Belt and is moving east. Growers in Nebraska are also battling ALS-resistant shattercane. And ALS resistant smooth pigweed was recently identified in Kentucky.
"Once weeds become resistant to ALS inhibitor herbicides, we lose the utility of these herbicides forever," says Gordon Harvey, weed scientist with the University of Wisconsin. "But by taking a proactive stance, farmers can delay the spread of ALS-resistant weeds and extend the useful life of these products."
The first step is to break the cycle of continuous ALS herbicide use by applying herbicides that have a different mode of action.
In soybeans, Kapusta says diphenyl ethers like Blazer, Cobra, Reflex and Flexstar are excellent alternatives to Pursuit. Diphenyl ethers control weeds by disrupting plant cell membranes. They provide broad spectrum broadleaf control and are effective against ALSresistant weeds like waterhemp. According to Martin, diphenyl ethers have also been highly effective against ALS-resistant smooth pigweed.
For best results on waterhemp in soybeans, Kapusta advises starting with a soilapplied herbicide like Treflan, Prowl, Frontier, Lasso or Dual. Then follow up with a nonALS postemergence treatment.
"Resistant weed populations can take over a field without much warning," says Fred Roeth, weed specialist with the University of Nebraska. "On a continuous ALS program, you can go from good control to only 60 percent control in just one year."
Because ALS resistance is transferred by pollen, it can spread quickly over fence lines, county lines, and even state lines, notes Roeth. "If farmers rotate early enough, they can keep ALS herbicides useful for a longer period of time."
There are over two dozen ALS inhibitor herbicides now registered for use on corn, soybeans and wheat. "Don't assume you're using a different mode of action just because you're using a different brand name," cautions Harvey. If you don't know what the mode of action is, you should find out before you spray.
In addition to herbicide rotation, Harvey recommends using one or more of these strategies:
* Tankmixing an ALS herbicide with a herbicide that uses a different mode of action.
* Rotary hoeing and cultivating. Tillage controls both resistant and non-resistant weeds.
* Using herbicides with very little potential for resistance to develop. (These would include chloroacetamides like TopNotch, Surpass, Harness, Dual, Lasso and Frontier, and growth regulators like 2,4-D and Banvel.)
* Rotating to a perennial like alfalfa where practical. Crops with different life cycles combat resistance by competing with different species of weeds.
"It's important to keep idle weeds guessing by using a variety of strategies for control," concludes Harvey.
This article courtesy of GrowthTech Communications
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