SEQUENTIAL USE OF SOME INSECTICIDES AGAINST COTTON BOLLWORMS IN CONTROL TRIALS

The effect of different insecticides in four rotations against the bollworms infesting cotton plants during three successive seasons was studied to determine the best sequence. Insecticides used were Cyper‌methrin (Cymbush) (pyrethroid); Profenofos (Curacron) (D.P.); Thiodi‌carb (Larvin) (carbamate) and Delfos (Dursban + XRD 473) (mixture). Tested insecticides were used in four different rotations as follows : A- Larvin then curacron then cymbush then delfos. 13- Cymbush then larvin then delfos then curacron. C- Curacron then delfos then larvin then cymbush. D-Delfos then cymbush then curacron then farvin. Sequences were evaluated according to their effectiveness in de‌clining the number of bollworms larvae in the treated plots as compared with the average number of the untreated plot, and the loss in cotton yield caused by bollworms infestation. 1-Reduction of larval population The programme beginning with thiodicarb was the best sequence in reducing the larval population of bollworms, while that beginning with profenofos was the least effective. The other programmes were nearly equal in their effect, and did not differ clearly from that beginning with thiodicarb. 2-Cotton yield loss Insecticides treated plots revealed the lowest cotton yield loss in comparison with untreated plots. Insecticides application reduced the in‌cidence of bollworms infestation on cotton and decreased the percent‌age loss in cotton yield.