Dimethenamid-p was labeled for preemergence use in potatoes in 2005. The herbicide provides hairy nightshade control; however, a tank-mix partner targeting common lambsquarters must be used in order to provide satisfactory control of that weed. S-metolachlor and metolachlor, also labeled for use in potato, are in the same chemical family as dimethenamid-p and questions have arisen as to whether or not these herbicides provide the same or different levels of hairy nightshade control. The objectives of this study, therefore, were (1) to compare preemergence control of common lambsquarters and other weeds in potato with dimethenamid-p applied at 0.72, 0.94, or 1.12 kg ai ha−1 alone or in two-way tank mixtures to determine appropriate tank-mix partners, and (2) to compare hairy nightshade control by dimethenamid-p with control by S-metolachlor or metolachlor. Two-way tank mixtures of dimethenamid-p with ethalfluralin, EPTC, flumioxazin, metribuzin, pendimethalin, or sulfentrazone generally improved season-long common lambsquarters control compared with dimethenamid-p applied alone at 0.72, 0.94, or 1.12 kg ha−1. When compared with control by dimethenamid-p alone at 0.72 or 0.94 kg ha−1, control by dimethenamid-p at either rate tank-mixed with ethalfluralin or EPTC was not improved as much as control by combinations of dimethenamid-p at those rates with the other tank-mix partners. Hairy nightshade control by three-way tank mixtures of S-metolachlor or metolachlor with various combinations of metribuzin, ethalfluralin, EPTC, or pendimethalin ranged from 60 to 86% and was not as great as the 93 to 98% control by dimethenamid-p at 0.72 kg ha−1 combined with the same tank-mix partners. U.S. No. 1 and total tuber yields of comparative two- and three-way tank mixtures were generally increased when weed control was improved.

Producers in the semiarid Great Plains are exploring alternative crop rotations, with the goal of replacing winter wheat–fallow. In 1993, a study was established to compare performance of eight rotations comprised of various combinations with winter wheat (W), spring wheat (SW), dry pea (Pea), safflower (Saf), corn (C), sunflower (Sun), proso millet (M), or fallow (F). After 8 years, we characterized weed communities by recording seedling emergence in each rotation. Seventeen species were observed, with downy brome, kochia, horseweed, and stinkgrass comprising 87% of the community. Rotations with the least number of weed seedlings were W–F and SW–W–C–Sun; in comparison, weed density was six-fold higher in W–M. Density of downy brome and kochia was highest in W–M compared with other rotations, whereas stinkgrass and green foxtail were prominent in proso millet of the W–M and W–C–M rotations. Horseweed established readily in safflower and dry pea. In the semiarid Great Plains, designing rotations in a cycle of four that includes cool- and warm-season crops can be a key component of integrated weed management.

In 2004 and 2005, field research was conducted in Idaho to compare tank mixtures of flumioxazin at the 53 g ai/ha potato use rate with comparable tank mixtures of rimsulfuron at 26 g ai/ha for broad-spectrum weed control. Flumioxazin in two-way tank mixtures with metribuzin, EPTC, pendimethalin, S-metolachlor, or ethalfluralin provided greater than 90% hairy nightshade control, which was comparable with control by similar rimsulfuron two-way tank mixtures. Flumioxazin plus metribuzin or rimsulfuron were the only two-way mixtures with flumioxazin consistently providing 90% or greater redroot pigweed, common lambsquarters, and green foxtail control. Control of these weeds by any of the rimsulfuron two-way mixtures was almost always greater than 90%. Three-way tank mixtures containing flumioxazin or rimsulfuron controlled hairy nightshade, redroot pigweed, and common lambsquarters similarly, and control ranged from 89 to 100%. When metribuzin was not included with flumioxazin in three-way mixtures, control was 80 to 97% and not always comparable with the 89 to 100% control by similar rimsulfuron mixtures. Green foxtail control by flumioxazin or rimsulfuron three-way mixtures usually was similar and greater than 90%.

Producers in the Great Plains are exploring alternative crop rotations with the goal of reducing the use of fallow. In 1990, a study was established with no-till practices to compare eight rotations comprising various combinations of winter wheat (W), spring wheat (SW), corn (C), chickpea (CP), dry pea (Pea), soybean (SB), or fallow (F). After 12 yr, we characterized weed communities by recording seedling emergence in each rotation. Downy brome, cheat, redroot pigweed, and green foxtail were the most common weeds observed. Weed community density was highest for W–CP, being 13-fold greater than with Pea–W–C–SB. Downy brome and cheat were rarely observed in rotations where winter wheat was grown only once every 3 or 4 yr; in contrast, density of the brome species was 75-fold greater in W–CP. Warm-season weeds were also affected by rotation design; density of redroot pigweed and green foxtail was sixfold greater in W–C–CP compared with Pea–W–C–SB or W–F. One rotation design that was especially favorable for low weed density was arranging crops in a cycle of four, with two cool-season crops followed by two warm-season crops.