The control of rice stem-borers (Lepidoptera: Pyralidae) by insecticides applied to the roots of rice plants

Abstract

AbstractExperiments were conducted in Bangladesh in April–July and July–December to study the effectiveness of three methods of insecticide application to three varieties of rice against the stem-borers Scirpophaga incertulas (Wlk.) and Chilo polychrysus (Meyr.). In April–July, seedlings of the varieties IR8 and Dacca-14 were uprooted when 22 days old and treated individually with 0·0375%, 0·075%, 0·15% or 0·3% diazinon (as Diazinon 60 EC), dicrotophos (as Bidrin 85 EC) or carbaryl (as Sevin 85 SP) or 0·3% γ-BHC dust for 12, followed by dipping for 12 h in fresh water and then transplantation. In July–December, the same treatments were applied by controlled irrigation to the seedbeds of the varieties IR8 and Dacca-25 and for 40 h when the seedlings were 24 days old. In another experiment in July–December, granular formulations of diazinon (as Diazinon 5G), dicrotophos (as Bidrin 5G) and Sevidol (a mixed formulation of carbaryl 8G plus γ-BHC 8G) were also applied to the transplanted field at an interval of 20 days. Insecticides applied to uprooted seedlings reduced borer populations more in the case of variety IR8 than in Dacca–14. Diazinon applied at 0·3% to the variety IR8 and Dacca–25 effectively reduced the borer population to 4–8 and 10·5%, respectively, for up to 41 days; γ-BHC applied to the seedbed did not show much response. Dicrotophos was not highly effective in controlling the borers. Granular formulations of Sevidol at 1–5, 2 and 2–5 kg a.i./ ha and diazinon at 2–5 kg a.i./ha controlled stem-borers more effectively in variety IR8 than in Dacca-25. Variety IR8 was found more susceptible to the stem-borers than Dacca-25 and Dacca-14.