Effect of Crop Rotation, Tillage, and Herbicide Treatment on the Evolution of ALS-Resistant Kochia after Four Years.

Combinations of cultural, mechanical, and chemical control practices are often recommended in agricultural settings to suppress weeds, however, few field studies have quantified the impact of integrated weed management programs on the evolution of herbicide resistant weed species. Kochia (Kochia scoparia) is a summer annual tumbleweed which has become one of the most problematic weed species in the Northern Great Plains, in part, to evolved resistance to various herbicides. Field studies were established in Lingle, Wyoming, Scottsbluff, Nebraska, and Huntley, Montana in 2014 and continued through 2017. ALS-resistant kochia was seeded at 2,000 g/ha within each of the study sites early May, 2014. Thus, a uniform population of ALS-resistant kochia was used to quantify the combined impacts of crop rotation, tillage, and herbicide use on the evolution of ALS-resistant kochia. Tillage treatments (main-plot) included annual intensive tillage or minimum tillage. Four crop rotations (split-plot) consisted of continuous corn, corn-sugarbeet, corn-dry bean-corn-sugarbeet, and corn-dry bean-wheat-sugarbeet. Herbicide treatments (split-split-plot) included complete reliance on ALS inhibitor herbicides, mixtures including ALS inhibitors and another effective mode of action, or an annual rotation between ALS herbicides and non-ALS herbicides. Kochia density were measured summer 2018 by marking a randomly placed 1 m² quadrant per plot. Each plot was then treated with an ALS herbicide and 1% COC. Exactly two weeks later, kochia densities were once again estimated within the same quadrant. Based on the results of this study, we may develop herbicide-resistant weed management recommendations that go beyond herbicide use pattern, therefore, decreasing the reliance on herbicides and possibly the evolution and spread of new herbicide-resistant weed species.