POTATO (SOLANUM-TUBEROSUM) RESPONSE TO SIMULATED DRIFT OF IMIDAZOLINONE HERBICIDES

Potato response to simulated drift of imazamethabenz, imazethapyr, or imazapyr was evaluated in field studies conducted near Aberdeen, ID, i n 1989 and 1990. Herbicides were applied at rates corresponding to 0.0 2, 0.1, and 0.5 times the typical use rate (x rate) of each herbicide. Simulated drift treatments were applied at potato emergence, tuber in itiation, or tuber bulking. Foliar injury symptoms varied with herbici de, rate, and potato growth stage at the time of application, but were generally most severe with imazapyr and least severe with imazamethab enz. Yield losses also varied with herbicide, rate, and potato growth stage at the time of application, but generally were greater when drif t occurred at tuber initiation or tuber bulking than at potato emergen ce. Losses in U.S. Number 1 (highest quality) yield were greater than losses in total yield, indicating that tuber quality was affected more by the herbicides than was tuber biomass accumulation. U.S. Number 1 yield was not reduced by simulated drift of imazamethabenz at 0.02x bu t was reduced 25% by the 0.1x rate applied at tuber bulking. At the 0. 5x rate, U.S. Number 1 yield was reduced 36, 85, or 92% when drift occ urred at potato emergence, tuber initiation, or tuber bulking, respect ively. For imazethapyr, U.S. Number 1 yield losses ranged from 0 to 68 % for the 0.02x rate; 19 to 98% for the 0.1x rate; and 64 to 100% with the 0.5x rate, depending on potato growth stage at the time of applic ation. Losses were least when drift occurred at potato emergence. Simu lated drift of imazapyr at the 0.02x rate applied as potatoes were eme rging reduced U.S. Number 1 yield 79%. All other imazapyr treatments c aused greater-than-or-equal-to 99% loss in U.S. Number 1 yield.