Management of Foliar Diseases in Bt Cotton with Agro-chemicals

摘要

Diseases cause serious loss to cotton production under favourable weather conditions. Among the foliar diseases, bacterial blight caused by Xanthomonas axonopodis pv. malvacearum and fungal foliar leaf spots caused by Alternaria macrospora, Myrothecium rordium and Cercospora gossypina are important. Heavy incidence of these diseases cause severe defoliation. Considering the importance of these diseases, a study was made with an objective to manage these diseases in Bt-cotton using agrochemicals at Faridkot and Ludhiana in 2006-07, 2007-08, and 2008-09 under natural epiphytotic conditions. The replicated trial was in a randomized block design. Bt hybrid MRC 6301 was sown during the second week of May, at a spacing of 75.0 x 67.5 cm in plots of 14.2 m(2) Six fungicide were followed propineb (Antracol 70 WP) @ 0.2%, 0.3%, 0.4%, copper oxychloride (Blitox 50 WP) @ 0.25%, mancozeb (Indofil M-45) @ 0.3% and copper oxychloride (Blitox 50 WP) @ 0.25% plus streptocycline sulphate @ 15 mu g/ml. Fungicides were sprayed thrice at an interval of 15 days starting from the initial appearance of the disease. Untreated plot were maintained as control. Final observations on disease severity were made 10 days after the last spray of fungicides using 0-4 disease scoring scale. Per cent disease incidence was calculated and finally per cent disease control was calculated. The pooled data of two seasons at Faridkot indicated that all the treatments were effective to check bacterial blight and fungal foliar leaf spots compared to control. Propineb 70 WP at all the test concentrations used effectively checked Alternaria leaf spots, but its efficacy was comparatively low in controlling bacterial blight and Myrothecium and Cercospora leaf spots. Copper oxychloride @ 0.25% was effective in controlling fungal leaf spots but its efficacy in checking bacterial blight was low compared to treatment with copper oxychloride plus streptocycline sulphate. The pooled data on seed cotton yield indicated that highest yield was obtained in its treatments with copper oxychloride with or without streptocycline sulphate. Results of Ludhiana location indicated that propineb was effective to check the development of Cercospora and Alternaria leaf spots at a higher concentration of 0.4 per cent during both the years. The pooled data indicated per cent disease control of 72.3 and 67.2 for Cercospora and Alternaria leaf spots, respectively. Copper oxychloride plus streptocycline sulphate recorded the highest disease control of 71.6 per cent for bacterial blight.