Glyphosate-resistant kochia ‘explodes’ in Kansas fields
Back in 2007, Kansas State University specialists confirmed the presence of glyphosate-resistant kochia in Kansas. In 2010, they added several confirmed sites of problems.
“Then, in 2011, it just exploded,” said Phil Stahlman, K-State Extension weed specialist, who gave a presentation on glyphosate resistance problems to Kansas soybean producers during the annual Kansas Soybean Expo in Salina on Jan. 11.
Stahlman said K-State scientists are confident that the presence of resistant kochia is commonplace throughout the western third of Kansas, and into eastern Colorado, southern Nebraska and the panhandle of Oklahoma.
“The worst problem is in postharvest fallow scenarios,” he said. “We’ve done quite a lot of work on surveying the problem, assessing how serious it is and developing some alternative control strategies for producers.”
• Last year, the populations of glyphosate resistant kochia erupted.
• Rotation and multiple modes of action are the best course of action.
• Some tillage may be the only option of control.
Stahlman said resistant kochia is easier to manage in corn or sorghum than it is in soybeans. It is hardest to handle in summer fallow.
“The best approach is to use preemergence dicambia early in the spring if you are rotating to sorghum or corn,” he said. “However, you have to be careful about carryover if you are going to plant soybeans or sunflowers. In fallow, the best approach is a gramaxone for preemergent treatment, followed by a photosynthetic inhibitor such as atrazine.
“We actually have a lot of alternative tools,” he said. “The problem is that in nearly all instances they are not as effective as glyphosate has been in the past, and they all cost more.”
He said that of 1,600 wheat-stubble fields surveyed in August, slightly more than 30% had been tilled to control kochia.
“I don’t know what that percentage would have been five years ago, but in my mind, returning to tillage is one of the things we have to accept as the possible consequence of glyphosate resistance.”
Kansas has also seen infestations of resistant waterhemp in the eastern part of the state, and an emerging problem with elevated tolerance to glyphosate in Palmer amaranth in Barton and Pawnee counties.
“It isn’t quite high enough to call it resistant, but we need to really watch it. We’re only a short time away from calling it resistant,” he said.
Stahlman advised producers to watch their rotations carefully and to change herbicide practices.
“You are going to need to apply a preemergent and follow up with postemergent Roundup,” he said. “And as we go forward, I cannot emphasize enough that you have to work with multiple modes of action.”
The encouraging thing, Stahlman said, is that producers are paying attention — and so are crop consultants and Extension agents.
“Only a few years ago, when we did surveys, we’d get fewer people being knowledgeable about resistance and even fewer than that that expressed concern. Now, we see people becoming very aware, and many of them are changing their weed-control programs. The message is getting through,” he said.
Stahlman said he talked to producers last summer about the possibility that they would have to do some tillage to control kochia.
“They said ‘Oh, no, I’m not going to do that,’ ” he reported. “But then they did. No one wants to go there, but sometimes there is not an alternative.”
Stahlman also said that producers need to be particularly vigilant early this spring for signs of infestation of winter-tolerant weeds that may have come up with the late fall rainfall.
“Early on, we didn’t have enough moisture to germinate weeds,” he said.
“Then we got rain, and if any of those winter annuals made it out of the ground, they could be much farther along than producers are used to looking for in February and March.
“I’d say be prepared to spray this month [February] if you spot a problem,” he said. “You don’t want those things to get away from you.”
This article published in the February, 2012 edition of KANSAS FARMER.