DICAMIBA ANTAGONIZES GRASS WEED-CONTROL WITH IMAZETHAPYR BY REDUCING FOLIAR ABSORPTION

Greenhouse and laboratory studies were conducted to determine the effe cts of tank-mixing the sodium salt of dicamba (Na-dicamba) with imazet hapyr on the efficacy and foliar absorption of imazethapyr, applied wi th non-ionic surfactant (MS) or methylated seed oil (MSG), by shatterc ane, giant foxtail, and large crabgrass. The effects of various salt f ormulations of dicamba and the addition of ammonium sulfate on efficac y, C-14-absorption and on foliar spray retention by the same species w ere also evaluated. Na-dicamba antagonized imazethapyr efficacy by red ucing C-14-absorption. Using MSO instead of NIS prevented antagonism w hen Na-dicamba was applied at 70 and 140 g/ha and reduced the severity of the antagonism at greater application rates by greatly increasing C-14-absorption compared to NIS. Reductions in C-14-absorption and spr ay retention were due to the salt formulations of dicamba rather than the parent acid. The addition of ammonium sulfate prevented dicamba an tagonism of imazethapyr toxicity to grassy weeds by maintaining C-14 f oliar absorption and spray retention at normal levels.