Study on the Seasonal Occurrence of Major Rice Insect Pests on Recommended Rice Varieties

Abstract

Recommended rice varieties RD 7, RD 11, RD 21, RD 23, RD 25, SP 60 and SP 90 were cultivated in teh fields in order to study the seasonal occurrence of insect pests. The experiment was conducted in the farmer's field in Tumbol Lam Luk Ka, Amphoe Lam Luk Ka, Pathum thani province both in teh wet and dry seasons of the years 1990 - 1990. None of insecticide were applied in the plots. The population of insect pests was weekly investigated by direct counting, using d-vac sucking machine, and sweep net. The result showed that rice leaf folder, Cnaphalocrocis medinalis Guenee, rice leafhoppers and planthoppers were pests of rice in dry season. Their population was found abundant during the tillering to booting stage of rice growth. The RD 23 variety was the most damaged by the rice leaffolder. In wet season, the rice insect pests were rice leafhoppers and planthoppers. They were found abundant on rice plant during tillering to booting stage. In milky stage rice bug, Leptocorisa spp. was found infested rice grain especially on variety SP 60. In wet season of 1990, population density of brown planthopper (BPH), Nilaparvata lugens (Stal) was found higher than the economic threshold (> 10 BPH/hill) on teh varieties RD 7, RD 25 and SP 60.