Manipulating within-orchard and adjacent habitats to provide better pest control in organic orchards. Some elements for modulating “orchard tree-pest-natural enemy” relationships

The control of pests in organic orchards cannot solely rely on the use of direct control methods. The effect of manipulating the habitat of orchard pests and natural enemies through tree architecture and the increase of plant diversity has been investigated in an experimental organic apple orchard and in a pear orchard, in order to provide information about the potential benefits of these cultural practices. Tree training affected the development of the most detrimental pests of apple trees, and the centrifugal training system globally provided better aphid (Dysaphis plantaginea) and mite (Panonychus ulmi) control than the more classical Solaxe system, whereas codling moth (Cydia pomonella) was favoured compared to Solaxe. The study of an experimental hedgerow designed to optimise protection of the pear orchard allowed us to validate the basic principles of designing plant assemblages to increase plant diversity in the orchard surroundings, namely the introduction of a succession of resources favouring the natural enemies of the key orchard pests, and to avoid detrimental effects (pests or diseases shared with the crops). This experiment and other studies suggest that manipulating the plant diversity adjacent to the orchard has an effect on entomocenosis. However, the potential benefits for the orchard only concern the control of pests that can be tolerated at high infestation rates.