Population dynamics and management of rice yellow stem borer Scirpophaga incertulas (Walker) and leaf folder Cnaphalocrocis medinalis (Guenee) in South Kerala

Abstract

The present study entitled “Population dynamics and management of rice yellow stem borer, Scirpophaga incertulas (Walker) and leaf folder, Cnaphalocrocis medinalis (Guenee) in South Kerala” was carried out at Department of Agricultural Entomology, College of Agriculture-Vellayani, from 2018 to 2021. A survey was conducted in major rice growing areas viz. Thiruvananthapuram, Onattukara and Kuttanad to study the population dynamics of rice stem borers and leaf folders in South Kerala in relation to biotic and abiotic factors. Field tolerance of different released varieties against rice stem borers and leaf folders and management studies were conducted at Onattukara Regional Agricultural Research Station, Kayamkulam. In addition to the common species of stem borer and leaf folder in rice, the white stem borer S. innotata was recorded from Onattukara and Kuttanad and the leaf folder species M. patnalis from Thiruvananthapuram and Onattukara. The lowest stem borer and leaf folder damage in rice was recorded in Kuttanad at 75 and 90 DAS respectively in southern Kerala. The major natural enemies recorded were the predators viz. dragonflies, damselflies, coccinellids and spiders and parasitoids viz.Cotesia sp, Isotima sp. and Tetrastichus sp. The rice varieties Samyuktha and Onam recorded significantly low stem borer infestation and Makom significantly low infestation by leaf folders. The highest phenol content was estimated in the rice variety Onam both at vegetative and flowering stages and highest silica content in Supriya and Sreyas. The bio-pesticides viz. 1% azadirachtin 0.003%, dasagavya 3%, cashewnut shell liquid 0.1% and T. japonicum and T. chilonis each 1 lakh ha-1 are effective in controlling stem borer and leaf folder infestation and safe to natural enemies. Significantly high grain yield and highest marginal benefit: cost ratio was recorded in the treatments chlorantraniliprole 18.5 SC 0.005% and 1% azadirachtin 0.003%. This study leads to the future investigations on identification of new species of stem borers, leaf folders and associated natural enemies. Breeding programmes can be taken up with tolerant varieties and management of these pests with new bio-pesticides can be done.