How weeds develop herbicide resistance

Just like people, weeds have natural genetic variations. And it’s those variations that allow some weeds to survive even though they’ve been sprayed with an herbicide.

Scott Nolte is a weed specialist at Texas A&M AgriLife Extension. He says a grower applies an herbicide and starts to notice that it doesn’t work anymore. Logically, the grower would think the herbicide is causing the issue.

"Growers are inadvertently selecting for a biotype or that specific weed that had a standing genetic mutation that allowed it to be resistant to that herbicide," says Nolte. "So, by applying that one herbicide or herbicide mode of action over and over, you eventually select for a population of weeds that has that genetic mutation."

He says if they are highly susceptible to an herbicide and everything around them is killed, there is nothing for the surviving weeds to cross-pollinate with. So, they can only reproduce the resistant biotype. Plants such as pigweed set out thousands of seeds and it’s very likely that some will have the mutation that allows them to survive.

Nolte recommends fighting back with multiple modes of action.

"The generally agreed upon method is tank mixing, multiple effective modes of action," he says. "So, when we say effective modes of action, it’s an herbicide that will essentially provide at least 80% or higher control of a weed species. And then, not allowing that one weed to escape."

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