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How do tillage, crop rotation and herbicides affect long-term, herbicide-resistant kochia management? The latest research from the University of Wyoming's plant sciences department explored the impacts of tillage, crop rotation and herbicide applications on kochia density (surviving and living plants), seed production (seeds per plant) and seedbank density (seeds in soil). Research explored tillage versus minimum tillage, four different crop rotations, and three in-crop herbicide regimes within each tillage and crop rotation. Intensive tillage in the spring with a rototiller to invert the soil (comparable to plowing and disking operations) mixed the top 4 inches of the soil. Soil in minimum-tillage plots was only disturbed when necessary because of harvest activities, such as with sugarbeets. The four crop rotations were continuous corn, corn-sugarbeet, corn- dry bean-corn-sugarbeet, and corn-dry bean-small grain-sugarbeet. The crops are common in Wyoming and also have diversity in canopy, planting and harvest dates. Three in-crop herbicide regimes were applied within each tillage and crop rotation treatment. The first was entirely ALS-inhibiting herbicides each year. The second was a tank mixture of ALS- inhibiting herbicides and a second mode of action to control ALS-resistant weeds. The last was an annual rotation of non- ALS-inhibiting herbicide one year, then ALS-inhibiting herbicides the next year. Herbicides were chosen for the highest labeled rate within the crop so as not to cause a carryover problem for subsequent crops. An annual spring tillage reduced kochia density better when compared to minimum tillage. Weed seeds were buried deep enough to block germination stimuli needed to trigger germination. This forces the seed to deplete energy reserves waiting for germination conditions and can kill the seed if that period is prolonged. This management is ideal for weed species with a short-lived seed life, such as kochia, whose seed life is approximately two years. Kochia plant densities were also the lowest in the most diverse crop rotation: corn-dry bean-small grain-sugarbeet. The two-crop rotation (corn-sugarbeet) showed the greatest kochia density, followed by continuous corn. These results prove the importance DIRT & 14 Sugar Producer MARCH 2021 What it costs to implement herbicide resistance management