In vitro evaluation of Dicloran 75 % WP as a new fungicide against Onion Bulb Rot Caused by Sclerotium rolfsii

Abstract

Big onion (Allium cepa L. var. cepa) is considered as one of the important cash crops cultivated mainly in dry zone in Sri Lanka. The crop is highly susceptible to pests and diseases due to its succulent nature. Among the diseases, fungal bulb rot caused by Sclerotium rolfsii is a prevalent disease that spread extensively during Maha season. Long term survival of Sclerotium in the soil has increased the threat of this highly devastating disease in Sri Lanka. There are recommended fungicides against the disease. However, the introduction of new, safer fungicides and revisiting the available fungicide is important for effective management of the disease. Therefore, this research was conducted to evaluate the efficacy of Dicloran 75% WP as an alternative fungicide to those that are already recommended. Each fungicide was tested at the concentrations of 100 ppm, 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm (a.i.). on the radial growth of Sclerotium rolfsii on Potato dextrose agar (PDA) medium by Petri plate assay. In conclusion, laboratory tests revealed that Thiophanate-methyl 50% + Thiram 30% WP inhibited Sclerotium rolfsii growth in a concentration-dependent manner, while Thiophanate methyl 70% showed no significant effect. Dicloran 75% WP stood out with a remarkable 76.54% inhibition at 2000 ppm, suggesting it as an effective fungicide for mitigating Sclerotium rolfsii impact in Sri Lankan onion cultivation. However, the study emphasizes the need for field trials to validate its real-world efficacy. While Dicloran 75% WP appears promising, additional research is crucial for practical feasibility and informed decision-making in sustainable onion disease management.