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.

Nomenclature: Dimethenamid-p; EPTC; ethalfluralin; metolachlor; metribuzin; pendimethalin; sulfentrazone; S-metolachlor; common lambsquarters, Chenopodium album L. CHEAL; green foxtail, Setaria viridis L. SETVI; hairy nightshade, Solanum sarrachoides Sendter SOLSA; redroot pigweed, Amaranthus retroflexus L. AMARE.