Repeated use of same chemical can lead to 'perfect storm'
By MATTHEW WEAVER
Researchers in Montana are investigating reports of glyphosate-resistant kochia.
Prashant Jha, assistant professor in Montana State University's Southern Agricultural Research Center in Huntley, Mont., said he is looking into reports of resistance to the herbicide in kochia in several fields.
Jha said there's been a visual confirmation based on grower complaints, but researchers will collect seed samples to confirm and document the level of resistance based on greenhouse and laboratory experiments.
Glyphosate-resistant kochia has also been found in South Dakota, Nebraska, Kansas and Canada.
"Any time you see a rapid expansion of resistance of any kind, particularly when it's moving closer to where you are, that's an area of concern," said weed researcher Ian Burke, Washington State University associate professor.
Burke recommends growers avoid making multiple, high-rate applications of glyphosate for any reason. They should diversify herbicides and reduce their reliance on a single type, he said.
Burke said the additional cost of diversifying inputs is one reason resistance management hasn't been more successful.
"The return on the investment of paying a little extra now is hard to justify, particularly when wheat prices are low," he said. "It's been a hard sell."
Nonglyphosate chemicals can be used to control glyphosate-resistant kochia, but aren't as effective on other weeds, said Utah State University Extension Agronomist Earl Creech. Tillage is another weed-management option. Loss of glyphosate could hinder no-till operations, he said.
Kochia is not prevalent in the Pacific Northwest, although it's appearing in some parts of the Columbia Basin around grain bins, Burke said.
Creech said the instances of glyphosate resistance are likely occurring because of improper use of the herbicide.
"If we don't use these chemicals properly and emphasize good stewardship, it could happen on our farm, too," he said.
Creech recommends being proactive, noting resistance can occur with any chemical. He recommends using the proper rate at the proper time in the proper place and rotating chemicals.
Using the same chemical year after year is "the perfect storm" for resistance to occur, he said. Once resistance to a herbicide has occurred in a particular field, it will last into the foreseeable future, Creech said.