Antifungal activity of aqueous extract of garlic and oils of carapa and neem on the causal agent of tomato late blight disease

This study evaluated the antifungal activity of plant extracts against Phytophthora infestans, the causal agent of tomato late blight. It was conducted in an insect-proof high tunnel using a randomized complete block design with three replicates. Treatments included aqueous garlic extract (0.2 g/mL), carapa oil (12% (v/v)) and neem oil (20% (v/v)), mancozeb 80 WP-based fungicide (5 g/L), and the untreated control. The biopesticides were applied once a week, while the chemical fungicide was applied once a fortnight. Applications were done before or after inoculation with 3×105 zoospores/mL of the pathogen. Recorded disease incidence varied from 50-100% for ancozeb to neem oil for preventive treatments and 100% for curative treatments. There was no significant difference in the severity of symptoms between aqueous garlic extract and mancozeb. The severity index ranged from 13.33 to 17.22% before inoculation to 20.0 to 25.0% after inoculation at the fruiting stage. The severity index of the untreated control was 58.34%. However, the net potential yield after inoculation with mancozeb (8.08 t/ha) was higher than that obtained with aqueous garlic extract (6.56 t/ha), carapa oil (4.95 t/ha), and neem oil (4.66 t/ha) compared to 4.55 t/ha for the untreated control. Hence, aqueous garlic extract can be used in integrated tomato late blight control programs.