ENHANCEMENT OF THIAZOPYR BIOEFFICACY BY INHIBITORS OF MONOOXYGENASES

The preceding paper described inhibition of thiazopyr metabolism in pl ant seedlings by inhibitors of cytochrome P450 monooxygenases, and the lack of inhibition by esterase inhibitors. We now describe greenhouse evaluation of the effects of these metabolic inhibitors on the bioeff icacy of thiazopyr. Inhibitors of cytochrome P450 monooxygenases, pipe ronyl butoxide (PBO), 1-aminobenzotriazole (ABT), metyrapone (MET) and tetcyclacis (TET), all enhanced the bioefficacy of thiazopyr against pigweed and other plant species. In contrast, inhibitors of esterases, tributyl phosphate (TBP) and triphenyl phosphate (TPP), produced only slight enhancement of thiazopyr activity. The effect of PBO was dose- dependent and was demonstrated against barnyardgrass, grain sorghum, r edroot pigweed, seedling johnsongrass, and giant foxtail. PBO demonstr ated no enhancement of thiazopyr activity in velvetleaf, tall morningg lory, cotton, or soybeans. Bioefficacy was most enhanced via exposure of seedling shoots to PBO and thiazopyr. The combination of results fr om the present and the preceding papers suggests that PBO enhances thi azopyr bioefficacy by effectively inhibiting thiazopyr metabolism in p lants.