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

•New oil-based dispersion with a half-life of T. asperellum conidia of 22.5 weeks.•Complete inhibition of P. megakarya on sprayed detached pods.•Enhanced rate and duration of protection on sprayed cacao pods in the field.•50% of pods protected 3.2 weeks after spraying in the field.•Formulation suitable for the spraying equipment of small-scale cacao producers.

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 22.5 weeks, versus 5 weeks 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 1 week, and 50% after 3.2 weeks. The formulations exercised a measurable effect for up to 7 weeks, versus 2 weeks in the case of an aqueous conidial suspension and 5 weeks 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.

Graphical abstractFormulated conidia of Trichoderma provide similar or even better protection of cacao pods against black pod disease than a conventional fungicide.Figure optionsDownload full-size imageDownload as PowerPoint slide