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

Abstract

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.