Farmers can either take steps to prevent herbicide resistant weeds from becoming a problem or they can wait until resistance develops and then try to figure out how to claw their way out of a mess.

Todd Baughman, Oklahoma State University agronomist at the Institute for Ag Biosciences in Ardmore, prefers door number one and says producers need to take an integrated approach to weed management to prevent resistance.

Baughman, speaking at the recent Oklahoma Peanut Expo in Lone Wolf, Okla., said the cheapest and most effective way to manage herbicide resistant weeds is to prevent the problem. And that’s not as hard as it might seem, considering some of the horror stories coming from areas where resistance has created significant management problems.

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“Start clean,” Baughman recommends. A yellow (pre-emergent) herbicide is a good start. “About 98 percent of Oklahoma’s peanut acreage is irrigated,” he said. That means farmers have the option of applying ample water to activate those yellow herbicides. “I would not plant a peanut without using a yellow herbicide. We can incorporate the material with water and the key is to apply enough water.  I prefer to put (pre-emergence) herbicides out through the system.”

He recommends from three-fourths to one inch of water to activate the herbicide. “And make certain every nozzle delivers that much water.”

Consider resistance in weed management strategies

Proper weed identification is another critical element in resistance management, he said. “Know how each herbicide works on a particular weed. Weed size is also a factor. It’s easier to kill the small ones. But they grow quickly, so determine how many acres you can spray in a day.”

He said farmers should buy good quality seed and strive for a healthy crop. “Also, rogue out the field if you see escapes. And manage weeds in turn rows, fence lines, corners and ditches.”

He advises combining the worst fields last to keep from spreading weed seed into clean fields. “Don’t plant something you can’t control later.”

Crop rotation can break weed cycles with different growing conditions and a different set of herbicides. “If grazing, graze the worst fields and then control weeds after pulling the cattle off.”

He said rotating chemistry is also important. The herbicide’s mode of action and site of action are important considerations in switching up products. “I am concerned about the pressure we may be putting on Valor herbicide,” Baughman said. “We often follow Valor with Cadre or Blazer and they all work on the same plant enzyme. We could see resistance to Valor.” He recommends adding another mode of action, something like Pursuit to the mix.