Improving the formulation and timing of application of endophytic biocontrol and chemical agents against frosty pod rot (Moniliophthora roreri) in cocoa (Theobroma cacao)

Frosty pod rot (FPR), caused by Moniliophthora roreri, reduces yields of cocoa (Theobroma cacao) by over 80% within a few years of disease outbreak. Both biological and chemical control approaches are being developed to supplement cultural management. Our objectives were to optimize the agent(s), their formulation and application regime for FPR control in Costa Rica. In order to economize scarce resources for field research, we opted for an iterative optimization of treatments. We aimed to (partly) replace copper hydroxide of proven efficacy with two systemic agents, the coevolved endophyte Trichoderma ovalisporum and the oxathiin flutolanil, and assessed four stickers for improving the agents' performance. Over 3 years, we selected effective agents and their combinations: eight of 18 treatments increased yields. Orthogonal contrasts extracted three general trends: (1) Copper should be applied in water, whereas the systemic agents were best formulated with a sticker. There was no difference between the stickers BreakThru and NP-7. (2) If the first rule was observed, a switch from systemic agent to the contact fungicide in mid season was beneficial. The optimum timing for this change requires further definition. (3) T. ovalisporum-containing agents controlled black pod better than flutolanil-based ones; both systemic agents were equally effective in controlling the more severe FPR. We discuss potential benefits of switching agents in the context of organic agriculture and argue that coevolved endophytes may be particularly suited for the classical biocontrol of Moniliophthora spp. in cocoa planted outside its South American centre of origin. (Résumé d'auteur