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Effects of shade trees on pests and diseases of Arabica coffee

Arabica coffee (Coffea arabica) may be monocropped, generally in intensive cropping systems. It is often grown under shade in agroforestry systems ranging from simple associations of two woody species to complex systems resembling natural ecosystems. The susceptibility of modern cropping systems, especially to pests and diseases, has partly been attributed to the loss of biodiversity. The present study revealed how shaded coffee cropping enables better pest and disease control.

Shade trees modify the microclimate and soil quality in coffee plantations. These modifications can alter pest and disease development through direct effects on their life cycle, or indirect effects via coffee defence mechanisms and stimulation of trophic chains. However, growing coffee under shade does not always reduce the pest and disease outbreak risk. The effects may vary depending on the organisms and their needs. Microclimate modifications that are unfavourable for coffee berry disease (Colletotrichum kahawae) development could, conversely, be conducive to the development of American leaf spot disease (Mycena citricolor) and the bark beetle (Hypothenemus hampei). Contrasting effects have also been noted in the same organism at different stages in its life cycle. Shade trees thus tend to reduce the berry load on coffee trees, in turn reducing their susceptibility to coffee rust (Hemileia vastatrix), while creating leaf moisture and temperature conditions suitable for fungus germination and penetration. Shade tree management for pest and disease control should thus be planned by taking all of the pests present into account, while seeking the shading balance point at which interesting ecological control mechanisms are stimulated and any negative effects are minimized.