Dynamic of Vascular Streak Dieback Disease Incidence on Susceptible Cacao Treated with Composted Plant Residues and <i>Trichoderma asperellum</i> in Field

<i>Trichoderma asperellum</i>, composted plant residues, and its combination can control vascular-streak dieback (VSD) disease caused by fungus <i>Ceratobasidium theobromae</i> in laboratory conditions. In this trial, we evaluated these treatments in two years through the application of foliar spraying and stem infusion for <i>T. asperellum</i> alone, through soil amendment for compost alone, and <i>T. asperellum</i> plus this organic fertilizer in the field on susceptible cacao clone. The disease is characterized by full-leaf chlorosis and necrosis that can develop rapidly to the entire branch, with around 70% incidence in seven months, and we detected the pathogen in branches showing light symptoms. All treatments except for <i>T. asperellum</i> plus composted plant residues three and seven months post application did not have any impact on the reduction of VSD incidence in the first year. In the second year, we observed a significant reduction of the disease by both <i>T. asperellum</i> in combination with compost and compost alone in a time span of three to seven months, and with <i>T. asperellum</i> spraying and infusion in a time span of five to seven months. By comparing to the control, the efficacy of these treatments in controlling the VSD disease seven months post-first application in the last year was 44.4%, 23.5%, 23.1%, and 15.1%, respectively. Detection of trees inoculated with <i>T. asperellum</i> indicated that this fungus was present in root and branch tissues except for treatment through infusions, while in the uninoculated trees, <i>Trichoderma</i> was not present or was present at a very low level. These data showed that combination of <i>T. asperellum</i> and composted plant residues applied through soil amendment was able to control VSD disease effectively and could potentially be used at large scale to control this disease and other diseases infesting aerial parts of cacao, and to improve soil fertility.