Efficacy of Trichoderma Asperellum oil formulations on the control of cocoa black pod disease (Phytophthora Megakarya)

The objective of this study was therefore to develop a formulation of conidia of T. asperellum with the aim of improving its efficacy. The formulations developed were oily dispersions. It was a combination of solvents consisting of groundnut oil or palm oil with structural agents and emulsifying-dispersing agents. Emulsification tests were carried out and the stability of the emulsions evaluated. The evaluation of the effect of co-formulants on the growth of conidia of T. asperellum was done by reading the optical densities of the formulated samples on multi-plates using a plate reader. The test on detached cocoa pods was done by treating the cocoa pods with selected formulations at 1.107 conidia/ml and inoculation of the treated cocoa pods was done 24 hours later with zoospores of P. megakarya at 1.105 zoospores/ml. The growth of necrosis on the fruits was measured daily. The screening of co-formulants and emulsification tests ended up with the selection of two formulations. The first composed of conidia of T. asperellum, groundnut oil, Tensiofix NTM® and Tensiofix 869®. The second differed from the first by utilisation of palm oil as the solvent. These formulations proved stable when diluted in water with 1% and 0.5% of sedimentation respectively after 24 hours. The viability test of the conidia indicated that the different formulations selected did not have a fungitoxic effect. The test on detached cocoa pods showed an improved efficacy of T. asperellum to control the disease. The growth rates of necrosis were 6.29 mm/day, 7.25 mm/day and 31.6 mm/day for treatment with formulation 1, pure conidia and control treated with water respectively. (Résumé d'auteur