Phytophthora seedling blight disease of cacao and its control measures

Abstract

Symptoms of Phytophthora seedling blight disease of cacao were found on 3 weeks old cacao seedlings at the nursery of Seed Production Division of Ghana Cocoa Board in New Tafo-Akim during routine surveys of cacao diseases in the Eastern Region of Ghana. Survey of seedlings in the nursery was conducted to determine disease incidence (DI). Heat sterilization of soil and drenching with Ridomil Gold plus 66 WP (6% metalaxyl-M and 60% copper (I) oxide) and Champion (77% cupric hydroxide) fungicides were evaluated for disease management. Symptoms of the disease started as vertical brown lesions above the cotyledon toward the top of cacao seedlings, causing the stems and leaves to wilt. Out of a total of 135,000 inspected cacao seedlings at the nursery, 2,525 (DI = 1.8%) seedlings were infected within one week of disease identification. Isolations from samples of infected tissues yielded Phytophthora palmivora. The fungicides were effective in disease control but heat sterilization of nursery soil before sowing cocoa beans was found to be the ideal control method. Key words: Seedling blight, cacao, Phytophthora palmivora, fungicides.