Impact of early season use of selected insecticides on cotton arthropod populations and yield.

Impact of five selected insecticides representing four insecticide classes (organophosphates, carbamates, pyrethroids, and formamidines) on cotton arthropod populations and yield was studied in Sunflower County, Miss., in the Mississippi delta in 1984. Applications of dimethoate, chlordimeform, fenvalerate, and flucythrinate (0.17, 0.14, 0.027, and 0.11 kg [AI]/ha) were made weekly during June to cotton that received three foliar treatments of dimethoate in May and cotton that received aldicarb (0.56 kg [AI]/ha) applied in the furrow at planting. Populations of most beneficial arthropods were reduced in the dimethoate, fenvalerate, and flucythrinate treatments to levels often significantly lower than those found in the control and chlordimeform treatment. Populations of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), were extremely high throughout the test; populations of the cotton fleahopper, Pseudatomoscelis seriatus (Reuter), reached damaging levels the last 2 weeks of June and first 2 weeks of July. Populations of both species were lowest in the dimethoate, fenvalerate, and flucythrinate treatments. Cotton in these treatments matured earlier and had significantly higher fruiting rates and yield increases as compared with the control and chlordimeform treatment. Few significant interactions were found between treatment with or without aldicarb for insect or fruiting and yield data. The control treatment with aldicarb had significantly higher yield than the untreated control. Tarnished plant bug and cotton fleahopper populations were reduced in the chlordimeform treatment compared with the control (especially nymphs of both species), and the chlordimeform treatment without aldicarb had a significantly higher yield than the control without aldicarb. Results of the test show that yield increases over that obtained in untreated cotton can be obtained by controlling damaging plant bug populations early in the season, and that several insecticides can be used.