Beet Armyworm (Lepidoptera: Noctuidae) Control on Cotton in Louisiana

Abstract

Efficacy of selected labeled and experimental insecticides against beet armyworm, Spodoptera exigua (Hübner), populations from Louisiana were determined in both a laboratory diet bioassay and in replicated field plots. Significantly higher LC 50 's for chlorpyrifos and thiodicarb were observed for one of two field-collected strains relative to a laboratory-reference strain in the laboratory diet bioassays. No significant differences in susceptibility between the reference strain and field-collected strains were observed for chlorfenapyr (proposed common name), spinosad or tebufenozide. For the reference strain, LC 50 's (ppm) for tebufenozide, spinosad, chlorfenapyr, chlorpyrifos, and thiodicarb were 2.6, 2.8, 4.8, 4.9, and 319.8, respectively. In two field tests, all three experimental insecticides (chlorfenapyr, spinosad, and tebufenozide) as well as chlorpyrifos significantly reduced the numbers of beet armyworm larvae relative to the untreated control at all sampling 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 significantly reduce the numbers of beet armyworm compared with the untreated control. The microbial insecticide Spod-X provided inadequate larval control in both tests.