RESPONSE OF SELECTED WEED SPECIES TO POSTEMERGENCE IMAZETHAPYR AND BENTAZON

Imazethapyr and bentazon were applied with petroleum oil adjuvant in a factorial arrangement to weed species in greenhouse and field researc h to determine if postemergence weed control by imazethapyr was antago nized when bentazon was tank-mixed. Tank-mixing 840 g/ha of bentazon w ith 13 or 27 g/ha of imazethapyr increased redroot pigweed and eastern black nightshade dry weight as compared to Colby's expected values in the greenhouse. However, weed control was not reduced in field studie s. Subsequent greenhouse studies indicated that soil interception and resulting root uptake of imazethapyr increased redroot pigweed control . Bentazon decreased foliar absorption of C-14-imazethapyr by 15% and translocation of C-14 from the treated leaf by more than 50% compared to C-14-imazethapyr applied alone. Nomenclature: Bentazon, -methylethy l)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide; imazethapyr, oxo- 1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid; eastern black nig htshade (Solanum ptycanthum Dun.) #(3) SOLPT; redroot pigweed (Amarant hus retroflexus L.) # AMARE.