Evaluation of Fungicides, Botanicals and Bioagents Against Leaf Spot Caused by Alternaria macrospora in Cotton*

Seven botanicals, nine bioagents, five systemic and seven non-systemic fungicides were evaluated in vitro on Alternaria macrospora, causing leaf spot of Bt-cotton. Among botanicals, garlic and onion bulb extracts at 7.5, 5.0 and 2.5 per cent concentrations, Trichoderma viride and T. harzianum both indigenous and exogenous strains among bioagents, tridemorph and difenoconazole at 0.075, 0.05and 0.025 per cent concentrations among systemic fungicides and iprodione and mancozeb among non-systemic fungicides at 0.15, 0.1 and 0.5 per cent concentrations were effective in inhibiting the mycelial growth of A. macrospora. Under field condition, all the above botanicals including Prosopis juliflora, bioagents and fungicides except difenoconazole were effective in reducing the incidence of Alternaria leaf spot of cotton. Least disease incidence (11.3 and 12.6) and maximum yield of 22.5 and 22.1 q/ha were recorded in iprodione and mancozeb treated plots, respectively. Further, mancozeb was effective under field condition with higher cost- benefit ratio of 1:9.1.