A new oil-based formulation of Trichoderma asperellum for the biological control of cacao black pod disease caused by Phytophthora megakarya

Abstract

In African cacao-producing countries, control of cacao black pod disease caused by Phytophthora megakarya is a priority. Introducing biological control agents as part of a P. megakarya control strategy is highly desirable, especially in a perspective of pesticide reduction. Trichoderma species are among the most used biological control agents. In Cameroon, Trichodermaasperellum formulated in wettable powder has produced positive effects against this disease. However, with this type of formulation, shelf-life and persistence of conidia on pods are limited. Our study therefore sought to develop a new T. asperellum formulation that would be more effective and better suited to the conditions of field application by small-scale producers in Cameroon. We selected a soybean oil-based oil dispersion, in which the half-life of the conidia reached 22.5weeks, versus 5weeks in aqueous suspension. Tested on detached pods, the formulation completely inhibited the development of the disease. When sprayed in the field on cacao clones highly sensitive to P. megakarya, the formulation resulted in 90% protection of treated pods after 1week, and 50% after 3.2weeks. The formulations exercised a measurable effect for up to 7weeks, versus 2weeks in the case of an aqueous conidial suspension and 5weeks for that of a conventional fungicide (Kocide). Trichodermaasperellum formulated in oil dispersion has therefore great potential for the control of cacao black pod disease with less recourse to synthetic fungicides. Moreover, this formulation is well adapted to the types of sprayers used by small-scale cacao producers in Cameroon.