Saikia, M. K.Patowary, Debarshi2024-01-122024-01-122021https://krishikosh.egranth.ac.in/handle/1/5810206219In the present investigation, efforts have been made to evaluate the comparative efficacy of two different forms of copper fungicides viz., copper oxychloride and copper hydroxide against late blight of potato incited by Phytophthora infestans (Mont.) de Bary under the different spray schedule (10 numbers of sprays at 4 days interval and 8 numbers of sprays at 5 days interval) with a view to select the most effective one for management of the disease. Field experiment performed revealed that both the fungicides could control late blight to a varying extent. Among the fungicides, copper hydroxide proved to be the best in reducing late blight severity. The fungicide could provide highest protection (73.74%) to moderately late blight resistant variety (Kufri Himalini) and 47.23% protection to the susceptible variety (Kufri Jyoti) when applied 10 numbers spray of copper hydroxide @0.2% at 4 days interval. This treatment gave maximum tuber yield 15.73 and 10.26 t/ha in K. Himalini and K. Jyoti respectively. Although maximum net return Rs. 54,200 with a corresponding incremental benefit-cost ratio of 2.25 was recorded in this treatment (10 numbers spray with copper hydroxide @0.2% at 4 days interval) but at the same rate of application the highest B:C ratio (2.41) obtained in the treatment of copper oxy-chloride with a net return of Rs. 43,500. An another study on comparative efficacy of four microbial bioformulations viz., Biometa, Biosona, Biollium and Biogreen against Red ant (Dorylus orientalis Westwood) on potato was evaluated during 2018-2019 and 2019-2020. The formulation, Biosona (combined tuber treatment @6g/kg tuber and soil application with enriched compost @ 2 t/ha) gave highest tuber yield of 11.23 t/ha with a minimum nfestation rate of 15.71% tuber damage and maximum protection (47.02%) against red ant and also gave a satisfactory profit of Rs. 19,700 with a B:C ratio of 1.48. The third investigation was carried out during 2018-2019 and 2019-2020 to evaluate the comparative efficacy of four microbial bio-formulations viz., Biometa, Biosona, Biolium and Biogreen against Aphid (Myzus persicae and Aphis gossypii) on potato. Biolium (Verticilium lecani) @0.5% spray gave highest tuber yield of 10.27 t/ha with a highest protection 33-66 % against aphid. This treatment gave a satisfactory profit of Rs. 10,400 with a B:C ratio of 1.44.EnglishThesis