Some studies on varietal resistance of rice crop and efficacy of insecticides to rice leaf-folder, Cnaphalocrocis medinalis [GN.]

Six rice varieties IR 6, KS 282, Bas. 370, Bas. 385, Bas. .Sup. and Bas. Pak. were screened to check their resistance against rice leaf- folder. None of the tested rice varieties were: free from the attack of rice leaf-folder, however, the infestation started in the second week of August and continued up to the last week of September. The highest larval population of rice leaf-folder was recorded on Bas. 370 which was followed by Bas. Pak., Bas. Sup., Bas. 385, KS 282 and IR 6. The infestation was 4.97, 3.97, 2.85, 2.63, 2.60 and 2.23 larvae per hill, respectively. Similarly the. highest leaves damaged per hill were observed on Bas. 370 which was followed by. Bas. Pak., Bas. Sup., Bas: 385, KS 282 and IR 6 having 21.12, 17.57; 10.68, 10.34, 9:.93 and 9.15 damaged leaves per hill, respectively. The rice varieties were evaluated, when the attack of rice leaf-folder. was at its peak, on the basis of percent damaged, leaves per hill, according to the "Standard Evaluation System" for rice crop (scale 1-9). The variety. IR 6 scored 1 (Resistant) while KS 282, Bas. 385 and Bas. Sup. scored 3 (Moderately resistant) and Bas.. Pak. and Bas. 370 scored 5 (Moderately, susceptible). In chemical control trial insecticides Karate 2.5 EC, Lorsban 40 EC and Nurelle-D 505 EC were applied two times at the rate of 494, 617 and 617 ml per hectare, respectively while Padan 4G, Furadan 3G and Thimet 5G were also applied two times at the rate of 22.2, 19.7 and 24.7 KG pct hectare, respectively. The mortality of rice leaf-folder, in percentage was calculated after 24, 48 and 72 hours and finally 10 days after application. All insecticides gave better control of rice leaf-folder than the check (untreated) plot. In first application, the best results were provided by Nurelle-D 505 EC followed by Karate 2.5 EC, Lorsban 40 EC, Padan 4G; Furadan 3G and Thirnet 5G showing 96.21, 95.44, 92.85, 89.63,87.86 and 84.75% larval mortality, respectively. In second application, Lorsban 40 EC ranked first with 98.65% larval mortality, followed by Karate 2.5 EC (98.19%), Nurelle-D 505 EC (94.43%); Padan 4G (91.65%), Furadan 3G (89.45%) and Thimet 5G (86.05%). The average of two applications showed that Karate 2.5 EC was the most effective insecticide against rice leaf-folder showing 96.81% larval mortality, followed by Lorsban 40 EC (95.60%) Nurelle-D 505 EC (95.32%), Padan 4G (90.64%), Furadan 3G (88.65%) and Thimet 5G (85.40%). The data of rice yield revealed that the average yield in the plots treated with insecticides ranged from 3.92 to 4.37 tons/ha as compared to the average yield in the check plots (3.19 tons/ha). The highest rice yield of 4.37 tons/ha was obtained with the insecticide Karate, followed by 4.26 tons/ha with Lorsban, 4.21 tons/ha with Nurelle-D, 4.18 tons/ha with Padan, 4.15 tons/ha with Furadan and 3.92 tons/ha with Thimet. The lowest rice yield (3.19 tons/ha) was recorded from the control (untreated) plots. The cost benefit ratio was also calculated. Maximum net profit (Rs. 11245) was obtained from karate followed by Lorsban (Rs. 10392), Nurelle-D (Rs. 9682), Padan (Rs. 8167), Furadan (Rs. 8118) and Thimet (Rs. 5547), respectively.