‘Olathe’ Pinto Bean (<i>Phaseolus vulgaris</i>) Response to Postemergence Imazethapyr and Bentazon

Abstract

Dry bean producers have limited postemergence broadleaf weed control options. The purpose of this research was to determine whether bentazon increased dry edible bean tolerance to postemergence imazethapyr applications. Imazethapyr and bentazon were applied with a petroleum oil adjuvant to ‘Olathe’ pinto bean in the field and greenhouse. Imazethapyr injured pinto bean 7 DAT in the field and greenhouse. Chlorophyll a content, a quantitative measure of bean chlorosis, decreased compared to the untreated control following imazethapyr application. When 840 g ha −1 of bentazon was tank-mixed with 53 g ha −1 of imazethapyr, bean injury decreased and chlorophyll a increased compared to imazethapyr alone. Fifty three g ha −1 of imazethapyr delayed physiological maturity by 8 and 15 d compared to the untreated control in 1991 and 1992, respectively. Pinto bean seed yields were not reduced compared to the untreated control. When 840 g ha −1 of bentazon was tank-mixed with 53 g ha −1 of imazethapyr, maturity was not delayed. 14 C-Imazethapyr absorption decreased by more than 40% and translocation of 14 C from the treated leaf decreased by more than 50% when 14 C-imazethapyr was tank-mixed with bentazon compared to 14 C-imazethapyr alone. The addition of 20 mM Na-acetate inhibited absorption of 14 C-imazethapyr, but did not inhibit translocation of 14 C. The decreased absorption and translocation of imazethapyr when tank-mixed with bentazon likely accounts for the safening effect observed in greenhouse and field studies.