Several enemies at the same time: interaction between two cocoa pod diseases and a cocoa pod borer and their impact in Peruvian agroforestry systems

Farmers frequently need to deal with several pests simultaneously. Despite this co-occurrence, damages produced by pests and diseases (P&D) are often studied and treated separately as they can be caused by distant taxa including fungi, nematodes and insects. P&D can enhance or hamper the incidence of each other, making of these interactions important modulators of the real impact of P&D on the plant. Interactions between P&D, abiotic conditions and resource availability can affect the composition of the P&D community at the temporal and spatial scale. Therefore, comprehensive analyses including all these factors are needed to better understand the spatio-temporal effect of P&D on crop production and to help design sustainable management strategies. In this preliminary study we explored spatio-temporal patterns in P&D incidence affecting cocoa agroforestry systems, their possible correlation with pod production and climate (mean temperature and precipitation), and potential spatio-temporal patterns of co-infection at the tree level in the Peruvian Amazon region of San Martin. Over the course of one year we collected data on the incidence of three cocoa pests: black pod disease (BPD) – due to Phytophtora palmivora, frosty pod rot disease (FPRD) – due to Moniliophtora roreri and the emergent local pest American cocoa pod borer (APB) - Carmenta foraseminis. Damages produced by other agents such as birds and sunburns were also recorded. We found that P&D incidence was correlated to total cocoa pod production. No geographical pattern was detected on P&D incidence profile suggesting that P&D population species are not expanding or contracting in the area and that none of the plots has enhancers or hampers that favour differently P&D incidences. FPRD is the prevalent diseases in the area, thus managing practices such as removal and proper elimination of infected pods need to be the priority in the region. We found that warmer temperatures were correlated to higher incidences of BPD and BPD+APB and drier conditions to damages produced by "other" agents. Correlation between P&D incidences and microclimatic conditions still need to be explored to better understand the effect of climate on P&D incidence and to provide recommendations to counteract this trend through microclimate manipulation. Neither temporal nor spatial conditions favour coinfection at the tree level, suggesting that pods are not a limiting resource in the area and that pests avoid interactions. Whether results are similar at pod level needs to be explored. 

Keywords: multipest, injury profile, pest interaction, spatio-temporal dynamics, pest emergence