Kansas State scientists have found kochia populations resistant to both dicamba and fluroxypyr in western Kansas. (Photo courtesy Phil Westra, Colorado State University)

ROCKVILLE, Md. (DTN) -- The tumbling tumbleweed just got a little bit harder to control.

Weed scientists at Kansas State University have confirmed populations of kochia in western Kansas that show cross resistance to both dicamba and fluroxypyr (Starane Ultra).

Dicamba resistance in kochia isn't new -- it was first documented in Montana in the mid-90s, and isolated populations have since been found in other Great Plains states like Nebraska, Colorado, Idaho and North Dakota, according to KSU weed scientist Vipan Kumar. Glyphosate resistance is also common in this troublesome annual weed.

"But this cross resistance is new for Kansas because fluroxypyr was working pretty well here and has been used a lot, especially in wheat, to take care of kochia," said Kumar, who led the KSU research. Fluroxypyr is a Group 4 herbicide that is a common ingredient in many herbicide premixes in wheat and corn.

The discovery could seriously complicate kochia control, especially if dicamba use continues to grow with the use of Xtend crops, Kumar said.

The good news is that the resistant weeds, which were identified near Garden City and Hays, Kansas, could have a "fitness cost," since that has been the case with other dicamba and fluroxypyr-resistant kochia populations identified in other states in the past, Kumar said.

That means the weeds could produce less seed and grow more slowly and eventually be out-competed by other susceptible weeds -- but only if dicamba and fluroxypyr aren't used on them for several generations.