Marigold is one of the most important commercially exploited flowers of the world. Among the diseases reported on marigold, leaf spot and flower blight of marigold caused by Alternaria tagetica is one of the most important diseases. The fungus was isolated from an infected marigold plant. The pathogenicity of the isolated fungus was proved by inoculating into the healthy seedling of marigold. Based on typical symptoms shown on the inoculated leaves, microscopic observations and cultural characteristics of the fungus, it was identified as Alternaria tagetica. An investigation was carried out in vitro to test the efficacy of botanicals, bioagents and fungicides against the isolated fungus. Among the botanical extracts tested, Garlic cloves (20%) extract recorded the highest percent mycelial growth inhibition with 78.25% followed by 10% (73.11%). The results of dual culture technique revealed that Trichoderma harzianum gives the highest with 46.82% mycelial growth inhibition. Among the tested fungicides, Mancozeb @ 0.2% showed maximum mycelial growth inhibition with 84.90% against Alternaria tagetica. The compatibility test of T. harzianum with fungicides revealed that T. harzianum was compatible with Mancozeb 75 WP and Copper oxychloride 50 WP but incompatible with Carbendazim 50 WP and Saaf 75WP at all concentrations.