Efficacy of selected biopesticides for the management of sheath blight of rice

Abstract

Studies on 'Efficacy of selected biopesticides for the management of sheath blight of rice' was conducted at the College of Horticulture, Kerala Agricultural University, Vellanikkara during 2000-2001. The major objective was to evolve a safer and eco-friendly management practice against sheath blight disease of rice. In vitro evaluation revealed Trichoderma viride and 2B as the best fungal and bacterial antagonists respectively. Fungi such as Aspergillus niger, A. terreus, Penicillium chermesinum, Cunninghamella bertholletiae and bacteria such as 1 B (Clostridium sp.), 4B, 7B (Bacillus sp.), lOB (Sporosarcina sp.), 19B (Bacillus sp.), 28B and Pseudomonas jluorescens showed significant inhibition of Rhizoctonia solani. Initial screening of the botanicals resulted in the selection of Chromolaena odorata, Leucaena leucocephala and Ocimum sanctum as the effective botanicals in the inhibition of R. solani. All these inhibited the formation of sclerotia even at five per cent concentration. Of the neem based formulations, Nimbecidine at 0.75 per cent concentration showed the maximum inhibition of 70.79 per cent and inhibited the sclerotial formation even at 0.5 per cent level. Comparative evaluation of microbial antagonists, botanicals and neem , based formulations were carried out in in vivo for the selection of potential ones to field experiment. In the present study T viride was selected as the best antagonist followed by 12B(Clostridium sp.), 28B, unidentified ascomycetes (20F), Acrophialophora sp., C. bertholletiae, Trichoderma sp. in that order. Among the botanicals C. odorata was the best as corroborated by the CODEX value of 3.56 and was followed by O. sanctum with a CODEX Value of five on 30th day of inoculation. Out of the two neem based formulations, Nimbecidine (azadirachtin 0.03%EC) showed the maximum control on the disease up to 30th day of inoculation (CODEX=1.17-2.29). The botanicals namely C. odorata, O. sanctum

and neem based formulation Nimbecidine were found as effective as carbendazim 0.1 per cent. The effect of bioagent T. viride, neem based formulation Nimbccidine as well as botanicals C. odorata, O. sanctum and fungicide carbendazim were tested under natural field condition. To select the most effective schedule, the different combinations of biopesticides for seed, soil and foliar applications were tried. Among the different biopesticides T. viride applied on seed, soil and foliage (T3) showed maximum disease control and was equally effective as carbendazim O.lper cent. Seed treatment cum soil application of T viride (T2) came next in reducing sheath blight infection and has given the highest benefit: cost ratio. Treatment T3 was also economically viable as carbendazim 0.1 per cent. An increase in the activity of phenylalanine ammonia lyase (PAL) was noticed with the foliar spray of T viride, Nimbecidine, C. odorata, and carbendazim.