A Comparison of Season-Long Cotton-Pest-Control Programs in California During 19661

Abstract

Five season-long insecticidal control programs were compared for their impact on pest and beneficial insects in a 240-acre cotton field. The pest species encountered were Lygus Hesperus Knight; the cabbage looper, Trichoplusia ni (Hubner); and the bollworm, Heliothis zea (Boddie). The beneficial insects assessed were a minute pirate bug, Orius tristicolor (White); a big-eyed bug, Gcoeoris pallnes Stal; a collops beetle, Gollops vittatus (Say); a damsel bug, Nabis americoferus Carayon; and a green lacewing, Chrysopa carnea Stephens. L. hespems was suppressed most effectively by 5 applications of toxaphene-malathion, 4 applications of Bidrin® (3-hydroxy- N, N -dimethyl- cis -crotonamide dimethyl phosphate), and 5 applications of toxaphene-DDT, All chemicals were applied when an average of 2 or more L. hesperus per 50 net sweeps was encountered. In another toxaphene-DDT program, 3 treatments applied each time an average of 10 L. hesperus per 50 net sweeps was found resulted in moderate reduction of this species. The abundance of L. hesperus in the control exceeded the recommended treatment level of 10 bugs per 50 net sweeps in 7 out of 13 weekly samples taken from June 6 to August 30. During the period of L. hesperus control, predator abundance was severely reduced in the toxaphene-malathion and the 2 Bidrin programs. It was moderately reduced where 5 applications of toxaphene-DDT were made and less severely so in the limited toxaphene-DDT program (3 applications). In August, an outbreak of cabbage looper occurred in all the chemical programs. By contrast, the control which had retained its predator populations suffered the lowest infestation and the least damage. One of the Bidrin programs was not treated and was extensively defoliated by cabbage looper. The other Bidrin program was treated at weekly intervals with Bacillus thuringiensis Berliner and was not seriously damaged. Two applications of toxaphene-DDT gave the most effective chemical control of cabbage looper. In late August and September, bollworm was significantly reduced in the programs receiving I and 3 applications of toxaphene-DDT, but unaffected by 3 applications of toxaphene-carbaryl and 4 of B. thuringiensis . The Bidrin program, which had been heavily defoliated by cabbage looper, was not treated for bollworm, yet the bollworm infestation remained below that found in the control. Four evaluations of boll set made during the season at periodic intervals showed no significant differences between any of the chemical programs and the control. However, in the final boll count made following the period of bollworm infestation the degree of bollworm damage was lowest in the 2 toxaphene-DDT programs followed by the Bidrin program, which had not been treated for bollworm. Correspondingly, at harvest, the highest yields were produced in the 2 toxaphene-DDT programs followed by the latter Bidrin program. But, only the toxaphene-DDT program which had received the least number of applications produced a significantly greater amount of cotton than the control.