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Weed & Pest

Concerns arise over herbicide resistant kochia

Written by Natasha Wheeler

“I think it’s important for people to be aware that glyphosate resistance has been confirmed so that we can take proper management action before it gets worse,” notes University of Wyoming Extension Educator Caitlin Youngquist.

Recently, a kochia plant was confirmed to have resistance to glyphosate – the active ingredient in Roundup and other herbicides.

“It was brought to my attention through Extension. I was able to coordinate with growers, the local Weed and Pest, the University of Wyoming (UW) research station and a weed specialist in Laramie,” Younquist explains.

A rapid-response bulletin was released, warning growers, homeowners and landowners to be on the lookout for additional cases. The announcement also included suggestions for herbicide alternatives, based on the crop or land being managed.

Weed management

“Herbicide stewardship is very important for preventing further spread of herbicide resistance,” Youngquist says.

If a herbicide-resistant weed is suspected, it should be destroyed, according to Gustavo Sbatella, assistant professor of irrigated crop and weed management at the Powell Research and Extension Center.

“Do not let it go to flower or seed,” Sbatella states.

The next step is to plan for herbicide rotation, changing the mode of action for controlling kochia weeds.

As an example, Sbatella explains, “If a farmer planted glyphosate-resistant sugarbeets and followed that with glyphosate-resistant corn, there is a possibility that the only herbicide that has been used in a two-year period is glyphosate. That puts a lot of selection pressure on any weed species, especially kochia.”

If those weeds begin to develop resistance, they may not be eliminated after herbicide treatments.

Identifying resistance

“If we have sprayed an area for any weed, and we notice that most of the plants where we have sprayed are dead or dying, but a few individuals are still thriving, that is a good indicator that we might have resistance there,” Youngquist notes.

“In the early stages of resistance, when we walk in the field, we are going to find some plants that are dying and some plants that are not. We will have different degrees after we spray in terms of plants that will die or survive,” comment Sbatella.

After other factors have been eliminated, such as spots that may have been skipped during herbicide application or tools that are not properly calibrated for even and accurate treatment, surviving plants may be an early indicator that alternate control methods are necessary.

“It’s important to be careful with the edges of our spray pattern,” Youngquist advises.

  Weeds along the perimeter of herbicide treatment may come into contact with the herbicide but not with a strong enough dose to be eliminated.

“Watch those areas where resistance can develop,” Youngquist suggests.

These areas also include ditches, roadsides, rights-of-way and other areas that have been repeatedly sprayed with the same herbicide, such as glyphosate.

Biology

“Kochia is an annual weed, and it is very common in much of the western U.S., including Wyoming,” Sbatella adds.

Kochia seeds spread very efficiently, and the plants are drought resistant and easily adapt to alkaline soils.

“It is one of the many tumbleweeds that we have here in Wyoming. It is probably one of the most common, along with Russian thistle,” he continues.

It is also one of the first weeds of the season to germinate. This time of year, the plants typically flower and produce large quantities of yellow pollen.

“They don’t have any flashy flowers,” Sbatella explains. “They are similar to ragweed in terms of how inconspicuous they are.”

Originally, kochia plants were introduced to the United States as ornamental plants, and they established easily in the western landscape.

“Along with downy brome, it is probably one of the worst weeds in the western U.S.,” mentions Sbatella.

Sugarbeets

Sugarbeet farmers in particular struggle with kochia infestations in their fields.

“With sugarbeets, we don’t have many herbicides that will effectively control kochia. We also don’t have as many modes of action as we do with other crops,” Sbatella explains.

When glyphosate-tolerant crops were introduced, kochia control improved dramatically.

“But, if we keep repeating the same treatments, with time it might lead to the development of herbicide resistance. That is probably one of the things we are seeing here,” he adds.

If resistance is suspected, Extension or local Weed and Pest agents can be contacted for assistance.

“Contact the local Extension office,” suggests Youngquist. “If the plant is resistant, remove it by any means necessary, such as pulling them by hand, mowing or spraying with alternative herbicides.”

Weed management experts in Wyoming are taking action and looking for solutions to control kochia.

“There is more to do, and it will require working closely with growers, landowners and right-of-way managers, such as railroad, county and city staff, to carefully manage how we spray and how we use herbicides for kochia and other weeds,” Youngquist says.

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at This email address is being protected from spambots. You need JavaScript enabled to view it..