Study on Mythimna separata to establish Economic threshold level in Rice

The yield loss by 1 to 15 larvae of Mythimna separata/hill ranged from 2.65 to 19.67 q/ha; with the cost benefit ratio of 1:0.77 to 1:5.76 in booting stage of the crop at the expected yield of 50 q/ha. At the expected yield of 50 q/ha, the yield loss by 1 to 15 larvae/hill ranged from 21.57 to 46.19 q/ha with the C/B ratios of 1:6.38 to 1:13.53. Considering the C/B ratio as 1:1, the economic threshold level resulted below 3.38 and 1.91 larvae/hill at the expected yields 50 q/ha. The economic threshold level at the panicle stage resulted < 1 larva/hill at the expected yields. In view of the above findings, it is recommended that the insecticide should be applied when the larval population of M. separata exceeded the economic threshold of 1 larva/hill at the panicle stage.