Some kochia populations in western North Dakota show resistance to Group 14 herbicides

(North Dakota State University/Supplied)

A North Dakota State University (NDSU) study suggests that some kochia populations in western North Dakota likely have developed resistance to commonly used pre-plant burndown herbicides.

Sold under the trade names Aim (carfentrazone) and Sharpen (saflufenacil), Group 14 herbicides are used by farmers to control kochia and other annual weeds.

In the NDSU study, a known susceptible kochia population was easily controlled by Aim and Sharpen. However, Aim showed very little activity on four kochia populations from across western North Dakota. Sharpen caused some necrosis on kochia leaves and stunted growth, but most plants survived and had two- to eight-inches of regrowth two weeks after treatment.

Brian Jenks, weed scientist at the NDSU North Central Research Extension Center, says kochia has been difficult to control during the prolonged drought of the past several years.

“Kochia thrives in dry conditions, and herbicides can be less effective when plants are drought-stressed,” he explains. “However, the NDSU study showed that recent lack of control is not due solely to drought stress, since plants survived these herbicides with little damage in the greenhouse.

“The potential loss of Aim and Sharpen as effective herbicides for kochia control is staggering because affected farmers will have limited control options remaining,” Jenks says.

Charles Geddes, weed scientist with Agriculture and Agri-Food Canada at Lethbridge, Alta., says this will be significant to all of North America.

NDSU recommends monitoring fields three to five days after applying pre-plant burndown herbicides to verify that weeds are being controlled. Kochia should be sprayed when small, and where possible, with multiple effective modes of action in a tank mix for burndown and post-emergence applications.

More to come.

Read more: The problem that is kochia