Field experiments were conducted over a 4-yr period, 1989 to 1992, in southern Manitoba to investigate potato (5. tuberosum) response to simulated drift of the dimethylamine salt of dicamba, 2.8 to 22.2 g ai ha–1; alkanolamine salt of clopyralid, 4 to 32 g ai ha–1; and tribenuron, 0.15 to 1.2 g ai ha–1. Rate ranges investigated corresponded to 2 to 16% of the recommended field rate for each herbicide. Dicamba at 22.2 g ai ha–1, clopyralid at 32 g ai ha–1, and tribenuron at 1.2 g ai ha–1 reduced total tuber yields 40, 29, and 41%, respectively, and marketable yields 74, 75, and 53%, respectively. Average weight of marketable-size tubers was unaffected by any treatment in any year. No tuber malformations were observed. Tubers produced on treated plants were planted the year following treatment to investigate the effects of simulated drift on subsequent tuber regrowth. Injury symptoms were evident for each herbicide in 2 out of 3 yr, but neither total nor marketable yields were affected.
