Terbufos and primisulfuron interactions were evaluated under growth chamber conditions using a sand culture system. Terbufos was applied to transplanted corn seedlings, followed in 5 d by foliar applications of primisulfuron plus nonionic surfactant. Primisulfuron and terbufos alone did not cause corn injury; however, shoot dry weight and shoot length were reduced 28 and 36% in terbufos treatments 96 h after primisulfuron application. Primisulfuron absorption and translocation were not affected by terbufos, but the half-life of primisulfuron increased from 2 to 3.5 h in terbufos treatments. Terbufos did not affect primisulfuron metabolite profiles. The basis for increased primisulfuron phytotoxicity in terbufos treatments appeared to result from reduced primisulfuron metabolism.
Benoxacor, CGA-185072, and MON-13900 were evaluated in laboratory studies as safeners to reduce injury caused by primisulfuron when corn has been previously treated with terbufos. Without safeners, shoot length was reduced 30% when primisulfuron (78 gm ha-1) followed terbufos (2.6 kg ha-1) applications. Stunting was significantly reduced by preemergence applications of CGA-185072 and MON-13900 at 200 g ai ha-1; however, shoot length was still reduced by 21 and 12%, respectively. Benoxacor did not reduce primisulfuron injury in corn previously treated with terbufos. Safening by CGA-185072 and MON-13900 was not due to reduced primisulfuron uptake or altered translocation. MON-13900 was further evaluated for its effects on primisulfuron metabolism. MON-13900 increased primisulfuron metabolism in terbufos-treated shoots by more than 50%. This increase in metabolism appears to be the mechanism of safening by MON-13900.
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