Comparative effects of Metalaxyl, Fosetyl-Al and cuprous oxide on the life cycles and control of Phytophthora palmivora, P. capsici and P. citrophthora on cacao seedlings (Theobroma cacao L.). In: Agrotrópica v. 10 p. 103-118, 1998.

Abstract

Metalaxyl was the best of the three fungicides examined in this study for control of P palmivora. P citrophthora and P capsici which cause black pod disease of cacao. Metalaxyl resulted in the greatest inhibition of mycelial growth (EC50 range: 0.046-l. 727 m g/ml); sporangium production (EC50 range: 0.061-l.113 mg/ml) and chlamydospore production (EC50 range: 0.012-0.198 m g/ml) for the three Phytophthora species. It was also the best fungicide at inhibiting bark and leaf lesions and chlamydospores formation in cacao tissue when applied as drenches at concentrations as low as lmg/g dry wt of soil. Of the three Phylophlhora species, P capsici was the least sensitive to metalaxyl with respect to mycelial growth. zoospore release, zoospore germination and zoospore formation. Phytophthora citrophthora was less sensitive to metalaxyl regarding chlamydospore germination and to a lesser extent chlamydospore formation in cacao tissue. Phytophthora palmivora was generally the most sensitive species to metalaxyl especially with regard to mycelial growth, zoospore release, chlamydospore germination. oospore production and chlamydospore fornation in cacao leaftissue. Cuprous oxide was also a very effective fungicide. It was highly fungitoxic to sporangium production and germination, chlamydospores production and germination, and oospore production by P capsici as compared to its much lower effect on mycelial growth. Fosetyl-AI was not the best fungicide for inhibiting any of the life cycle stages of the species of Phyt ophth ora tested, however, it had an outstanding effect on sporangium production and germination, chlamydospore production and oospore production. In vim it did not provide adequate control of leaf and stem lesions of cacao induced by the three Phytophthora species.