BEET ARMYWORM (LEPIDOPTERA, NOCTUIDAE) CONTROL ON COTTON IN LOUISIANA

Efficacy of selected labeled and experimental insecticides against bee t armyworm, Spodoptera exigua (Hubner): populations from Louisiana wer e determined in both a laboratory diet bioassay and in replicated fiel d plots. Significantly higher LC(50)'s for chlorpyrifos and thiodicarb mere observed for one of two field-collected strains relative to a la boratory-reference strain in the laboratory diet bioassays. No signifi cant differences in susceptibility between the reference strain and fi eld-collected strains were observed for chlorfenapyr (proposed common name), spinosad or tebufenozide. For the reference strain, LC(50)'s (p pm) for tebufenozide, spinosad, chlorfenapyr, chlorpyrifos, and thiodi carb were 2.6, 2.8, 4.8, 4.9, and 319.8, respectively. In two field te sts, all three experimental insecticides (chlorfenapyr; spinosad, and tebufenozide) as well as chlorpyrifos significantly reduced the number s of beet armyworm larvae relative to the untreated control at all sam pling periods (3, 5, 7, and 10 days after treatment), except for Test 2 at 3 days after treatment. Thiodicarb provided satisfactory control of larvae in Test 1; however, in Test 2 thiodicarb did not significant ly reduce the numbers of beet armyworm compared with the untreated con trol. The microbial insecticide Spod-X provided inadequate larval cont rol in both tests.