The cumin blight disease caused by the fungus Alternaria burnsii is the most destructive disease on cumin in its cultivated areas in the world. The fungus A. burnsii was isolated from cumin plants infected with blight and its pathogenicity was confirmed on cumin plants. Selected green chemicals (potassium silicate; PS and nano silicon; NSi) were evaluated for their antagonistic effect against A. burnsii in the laboratory at different concentrations (50, 100, 200, 300 and 400 ppm for PS and 1.5, 2, 2.5, 3 and 3.5 mM for NSi). Also, the inhibitory effect of Trichoderma harzianum and T. hamatum was studied in the laboratory using dual culture technique. The biocontrol fungus T. harzianum was formulated in four biofungicidal forms and tested against cumin blight in greenhouse and field trials. These forms were: suspension of fresh spores and mycelium in water, emulsion of fresh spores and mycelium with its filtrate in corn oil, emulsion of fresh spores and mycelium without its filtrate in corn oil, and emulsion of dried spores in corn oil, which were all sprayed on cumin plants showing blight symptoms. The emulsion of dried spores of T. harzianum at 1 × 10⁶ spores/ml was the most effective in suppressing blight disease, and NSi was in the second place in this regard, thus increasing the yield of seeds and the percentage of volatile oil in the seed compared to the untreated control.