Two sets field experiments were carried out at the College of Agriculture, Iroishemba, Imphal during Kharif, 2018 to study the effect of planting dates on the incidence of yellow stem borer, Scirpophaga incertulus Walker and leaf folder, Cnaphalocrosis medinalis Guenee, and to evaluate the bio-efficacy of certain new molecular inscticides against these pests in Rice crop var. KD-2-6-3. The planting dates had significant effect on the incidence of the pests. Early planted crop recorded significantly lower population than in the late planted crop. The mean of the various observation intervals' data revealed that the lowest S. incertulas incidence with 2.80% dead heart(DH) and 4.00% white ear head (WEH) was noticed in 30th June planted crop, followed by 15th July planted crop (5.01% DH & 6.24% WEH) and highest DH and WEH incidence (9.79% DH & 10.07% WEH) recorded in the crop planted on 14th August. The significantly lowest C. medinalis incidence was also observed in the early planted crop (30th June) with a mean leaf damage of 2.29%, the late crop (14th August) which witnessed the highest leaf damage (6.46%). The results on the efficacy of insecticides against the pests revealed that Ranaxypyr 20 SC @ 150 ml/ha proved to be the most effective treatment in controlling the S. incertulas with a mean minimum DH and WEH incidence of 2.62 and 0.90%, respectively, while Camphor oil @ 1000 ml/ha recorded maximum incidence of DH (5.39%) & WEH (3.27%). Against the leaf folder also Ranaxypyr 20 SC registered the lowest leaf damage of 2.25% closely followed by Neemazal @ 1000 ml/ha with a record of 2.71% leaf damage but differed significantly between them. The highest mean grain yield (5.25 t/ha) was harvested from the plots treated with Ranaxypyr 20 SC which showed non significant difference with the plots of Dinotefuran 20 SG @ 200 g/ha(5.10 t/ha) and Neemazal (5.08 t/ha), whereas Camphor oil treated plots accrued significantly lowest grain yield of 4.25 t/ha. The extent of avoidable yield loss due to the incidence of pests was estimated to be 24.57% in untreated control which was reduced to 2.85-19.04%;minimum being recorded in Dinotefuran 20 SG and maximum in Camphor oil treatments. The net profit of the insecticidal treatments varied from Rs. 5050.00 to Rs. 41580.00, the minimum being in Camphor oil and maximum in Ranaxypyr 20 SC treatments with the cost : benefit ratios of 1:0.93 and 1: 10.61, respectively.
