Two field experiments were carried out at Mallawi Agricultural Research Station Farm Minia, during 2005 and 2006 cotton growing seasons to evaluate the effect of defoliants dropp (Thidiazuron), ethrel (ethephon) and calcium superphosphate on the leaf shedding, earlinessand the yield of Giza 83 cotton cultivar, as well as their effects in controlling some insect pests and natural enemies in cotton. Results of this study could be summarized as follows:
In both seasons, dropp and ethrel gave a significant pronounced increase in leaf abscission%, earliness% and the number of bolls opening per plant as compared with the control. Also, dropp and ethrel tended to Increase lint % but to decrease boll weight and seed index. In contrast control and calcium superphosphate showed no significant effect on all agronomic characters in both seasons. Seed cotton yield was not significantly affected by any treatment in both seasons.
Dropp caused a significant reduction in the aphids and the spider mite infestations.
The calcium superphosphate caused a significant reduction in jassids and whitefly infestations.
Defoliants caused a significant effect on immature stages population of whitefly and increased the parasitism percentage to (86.15%) as compared with 62% in control.
Defoliants reduction of the bollworms infestation and the number of larvae was 14% and 10 larvae when calcium superphosphate was used 6th weeks after spraying.
Dropp caused the highest reduction in the bollworm infestation rates (94.12%).
Dropp caused a significant effect in reducing the loss of the cotton yield of 17.07% compared with 27.39% in control.