Composted plant residue amendments in integration with Trichoderma asperellum suppresses above-ground diseases and improves the growth of cacao (Theobroma cacao L.)

Cacao (Theobroma cacao L.) suffers severe losses due to infectious and non-infectious diseases. This work reports the potential of three formulations of composted plant residues in combination with Trichoderma asperellum to reduce these cacao diseases. All formula consisted of gliricidia and rice straw. In addition, the first compost contained empty stalks of oil palm fruit, the second contained billygoat weed, and the third compost had coconut husks. These three composts formula plus T. asperellum were applied through soil amendment. Then, their impact was evaluated on significant above-ground diseases, specifically vascular streak dieback (VSD) and Phytophthora pod rot (PPR), availability of NPK for the plant, and decreased Ni content in the plant. By comparing to the control, the efficacy of first, second, and third compost plus T. asperelum in controlling VSD was 73%, 68%, 72%, and PPR 65%, 51%, and 59%, respectively five months post-application in the first year. In the second year, the efficacy against the disease was higher than in the first year. It was 83%, 75%, and 58% for VSD and 69%, 61%, and 78% for PPR, respectively. Moreover, the treatments increased pod production and P content in the leaves, while N and K content rose just in treating the second and third compost plus Trichoderma. Ni content only decreased in the treatment of the first compost plus Trichoderma. These data showed that especially first compost in integration with T. asperellum treatment suppressed above ground diseases and increased cacao pod production. Therefore, disease management and cacao growth on a bigger scale could potentially use the Trichoderma integrated-composted plant residues.