The spread of glyphosate-resistant kochia is threatening no-till practices in some areas of the U.S., says Kansas State University.
The weed — capable of reaching 7 feet tall with roots that can grow as deep as 16 feet during a drought — is causing no-tillers to resort to tillage practices for control, the university reported. In the fall of 2010, Kansas State weed scientist Phil Stahlman and graduate student Amar Godar rated 1,500 wheat stubble fields with glyphosate-resistant kochia and discovered about 30% were tilled as an effort to terminate the weed. Most tillage occurred after a spray application was unsuccessful.
It’s a trend that could be rising as the weed continues to spread throughout North America. Kansas State says last year glyphosate-resistant kochia spanned from the Texas High Plains up to the prairies in Canada. And it may be heading even farther out west. Last month, the Pacific Northwest Pest Alert Network posted an alert to Idaho and Oregon growers about a possible case of glyphosate-resistant kochia in sugarbeet fields.
No-till advocates don’t want to see any further spread in tillage being the answer. “If we till the soil to manage kochia, we’ve lost the conservation gains we made in the last decade or more of using no-till,” Stahlman says.
The good news is there are effective management practices that don’t involve tillage. Stahlman and other researchers launched an effort to investigate alternatives to glyphosate for kochia, and discovered in research that if an herbicide with residual properties was applied before the weed emerged in early spring, emergence was cut by at least 70% to 80% — often more than 90%.
The seed life of kochia is also relatively short — no more than 2 to 3 years, so burying the weed seeds through tillage may preserve them and extend their dormancy, the Government of Saskatchewan says. Leaving them on the surface can increase their degradation due to weather, predators and disease.
If a no-tiller finds chemical control isn’t enough, the Government of Saskatchewan says close mowing will provide nearly the same effect as tillage while retaining the benefits of zero-till. But it’s possible that no matter how close the mow, kochia could regrow from buds below the cut line.
Another alternative is to underseed sweet clover with the previous crop to compete with kochia. Sweet clover has been found to reduce the emergence of kochia by 80% where it was seeded as a forage crop or as a green manure crop on fallow land, compared to conventional fallow.
Have you had problems with resistant kochia in your fields? How did you control it? Send me an e-mail at firstname.lastname@example.org and let me know.