Greenhouse and laboratory studies were conducted to determine the physiological basis for CGA-248757 and flumiclorac selectivity in five plant species. CGA-248757 and flumiclorac selectively control weeds postemergence (POST) by inhibiting protoporphyrinogen oxidase (Protox). Injury symptoms from CGA-248757 and flumiclorac include rapid desiccation and necrosis similar to injury from diphenyl ether and bipyridinium herbicides. Species sensitivity to CGA-248757 and flumiclorac was evaluated by comparing the dry weight reduction from POST applications. Abutilon theophrasti was sensitive to both herbicides, Amaranthus retroflexus was more sensitive to flumiclorac than CGA-248757, Brassica kaber was sensitive to CGA-248757 but tolerant of flumiclorac, and Zea mays and Glycine max were tolerant of both herbicides. Studies evaluated CGA-248757 and flumiclorac retention, absorption, translocation, and metabolism. Enhanced herbicide metabolism contributed to the tolerance of A. retroflexus to CGA-248757 and B. kaber to flumiclorac. Decreased herbicide retention, absorption, and translocation coupled with increased metabolism contributed to Z. mays tolerance of CGA-248757 and flumiclorac. Decreased herbicide retention and increased herbicide metabolism provided G. max tolerance of both herbicides.

Nomenclature: CGA-248757, [[2-chloro-4-fluoro-5-[(tetrahydro-3-oxo-1H, 3H-[1,3,4]thiadiazolo[3,4-a]pyridazin-1-ylidene)amino]phenyl]thio]acetate; flumiclorac; Abutilon theophrasti Medicus ABUTH, velvetleaf; Amaranthus retroflexus L. AMARE, redroot pigweed; Brassica kaber (D.C.) L.C. Wheeler SINAR, wild mustard; Glycine max (L.) Merr.'Conrad,' soybean; Zea mays L.'Pioneer 3751,' corn.