COMBINED EFFECTS OF ACETOLACTATE SYNTHASE-INHIBITING HERBICIDES WITH TERBUFOS AND PIPERONYL BUTOXIDE ON CORN (ZEA-MAYS) AND SOYBEAN (GLYCINE-MAX)

Greenhouse studies were conducted to determine the response of six cor n hybrids and two soybean varieties to acetolactate synthase (ALS) inh ibitor herbicides applied with terbufos and/or piperonyl butoxide (PBO ), a mixed function oxidase (MFO) inhibitor. Field experiments also we re conducted to determine the response of six corn hybrids to the comb ination treatments, terbufos plus ALS inhibitor herbicides and/or PBO and/or antidote. PBO at 0.33 kg/ha tank-mixed with nicosulfuron and pr imisulfuron injured the Northrup King 9283 corn hybrid. Great Lakes 58 4 corn was less sensitive than Northrup King 9283 to these combination treatments. Pioneer 3377 LR corn hybrid was resistant to the combinat ion of nicosulfuron or primisulfuron plus PBO at 2 kg/ha and also to t he combination treatments of imazethapyr herbicide plus PBO even thoug h terbufos was previously applied. ICI 8532 IT, ICI 8532, and Pioneer 3377 hybrids were injured by the combination of nicosulfuron or primis ulfuron and/or terbufos and/or PBO at 2 kg/ha. ICI 8532 IT corn hybrid was not injured by the combination treatment of imazethapyr or thifen sulfuron and terbufos. In the field studies, Pioneer 3377 IR and Ciba 4393 RSC hybrids were resistant to sulfonylurea and imidazolinone herb icides even when applied with PBO regardless of the presence of terbuf os. All treatments of chlorimuron plus terbufos caused considerable in jury to ICI 8532 IT, ICI 8532, Pioneer 3377, and Ciba 4393, but not Pi oneer 3377 IR and Ciba 4393 RSC. The combination of thifensulfuron wit h PBO injured Elgin '87 soybean, but the W20 soybean was tolerant to t his combination treatment. Combination of imazethapyr with PBO did not affect the growth of Elgin '87 soybean.