Kochia has now gained cross resistance in at least one state to both dicamba and fluroxypyr. Kansas State University (KSU) weed scientists said kochia showed this cross resistance in two areas on the west side of the state.
Dicamba-resistant kochia was first identified as early as the 1990s and glyphosate resistance also has become common in parts of the western Corn Belt. But this cross resistance, will complicate kochia management.
Fluroxypyr was working “pretty well” in Kansas to control kochia in wheat, says Vipan Kumar, a Kansas State University weed scientists. Fluroxypyr is a Group 4 herbicide that is a common ingredient in many herbicide premixes in wheat and corn.
KSU researchers collected seed from plants in one problem area near Garden City and grew them out for testing, then applied field-use rates of dicamba and fluroxypyr. With dicamba, survivorship ranged from 78% to 100%. Where fluroxypyr was applied, survivorship ran 85% to 100%.
At this point, weed scientists can’t say to what extent this co-resistance will lead to a “fitness cost” among these populations. So far, kochia populations that show resistance to dicamba and fluroxypyr tend to produce fewer seeds and grow less aggressively.
If that’s the case, the resistant populations might eventually fade into the background, provided growers pull back on using dicamba and fluroxypyr for a period of time.