Effect of fertilization and biocontrol application frequency on cocoa pod diseases

Three native and two commercial biocontrol agents (Clonostachys rosea and Trichoderma spp.) were evaluated against the cocoa diseases moniliasis, witches'' broom, and black pod. Antagonists were applied either separately or as mixed inoculum in comparison with a copper fungicide and a nontreated control. Cultural control (weekly removal of diseased pods) was practiced in all treatments. Field trials were conducted on neglected cocoa farms in eastern Peru from 1998 to 2000. The fungicide treatment and C. rosea strain G-4 did not reduce disease. The other single-strain antagonists reduced moniliasis. Additionally, Trichoderma longibrachiatum and Trichoderma stromaticum reduced witches'' broom and Trichoderma virens reduced black pod. With strain mixtures, yield increases of up to 15% were obtained. A mixture of four antagonists was superior to mixtures of two or three antagonists with respect to multiple disease control and yield. Biocontrol in combination with cultural control was more economical than cultural control alone; chemical control was least economical. Fertilization improved yields by 11% independent of the disease control measure and compensated for the additional costs with net returns improving by 9%. Increasing application frequencies of a mixed biocontrol inoculum improved moniliasis and witches'' broom control linearly. Moniliasis exhibited a stronger response. Witches'' broom was significantly lower than the nontreated control only if ten applications were administered in two-week intervals. This application frequency increased yields by 15%. It was followed by three applications adjusted to the production cycle (yield increase: 12%). Three adjusted applications were the most economical biocontrol strategy under the conditions of eastern Peru. Net returns were increased by 12%. Recommendations for technology transfer are presented. [Copyright &y& Elsevier]