In vitro efficacy of oomycete-specific fungicides and pH-modulated Bordeaux mixture against Phytophthora meadii of arecanut fruit rot

Abstract

Fruit rot disease or Koleroga, caused by Phytophthora meadii, is a serious disease of arecanut (Areca catechu L.) in the Western Ghats of India, causing major economic losses. The study evaluated the curative efficacy of selected oomycete-specific fungicides and the effect of pH on Bordeaux mixture against P. meadii using a detached nut assay in farmer’s participatory mode. Healthy ‘Sagara Local’ nuts were inoculated with a zoospore suspension of P. meadii and treated with Bordeaux mixture (1%) at pH 6, 7 and 10, Metalaxyl (4%) + Mancozeb 64% WP (0.25%), Mandipropamid 23% SC (0.1%) and Copper oxychloride 50% WP (0.25%). An untreated inoculated control was maintained. After seven days of incubation under high humidity, disease incidence was recorded. The untreated control showed 100 per cent disease incidence, while all other treatments significantly reduced fruit rot disease. Metalaxyl + Mancozeb was found to be most effective (10% incidence; 90% reduction), followed by Mandipropamid (20% and 80% reduction). Bordeaux mixture at pH 7 found superior (24% incidence), compared to pH 6 (36% incidence) and pH 10 (60% incidence). The results highlighted the effectiveness of Metalaxyl + Mancozeb, Mandipropamid and emphasize maintaining neutral pH in Bordeaux mixture for improved management of arecanut fruit rot.