Peach orchard protection strategies and aphid communities: towards an integrated agroecosystem approach
Résumé
Aphid populations, including a widespread pest, Myzus persicae, are known to be affected by cultural practices, plant growth and natural regulation, but their control in orchards most frequently relies on regular treatments aiming to avoid direct damage and virus transmission. This study aimed first at characterising farmers’ management strategies towards aphids and, secondly evaluating them in terms of efficiency and impact on aphid natural enemies. Protection methods were first identified through semi-open interviews and peach orchard pesticide records from 19 organic and conventional fruit farms in south-eastern France. It appeared that in addition to the regular use of direct control, farmers also used cultural and/or alternative methods and various decision-making indicators to optimise their orchard crop protection. Comprehensive variables based on the technical guidelines of the IOBC (International Organisation for Biological and Integrated Control) for crop protection made it possible to differentiate four strategies: intensive, optimised, input-substitution and integrated. Visual monitoring of aphid infestations and of beneficial populations was performed at the plot level. Brachycaudus schwartzi and Myzus varians were the most frequently encountered aphid species but the structures of the communities were affected by protection strategies: the more integrated the strategy, the more diverse and abundant the aphids. The two most effective strategies were dominated by chemical treatments, whereas the other two, less detrimental to aphid antagonists, were mostly carried out by organic farmers. Variations in aphid communities were related to: (i) the use of toxic products, correlated with low-infestations and low-abundance and diversity of antagonists; (ii) alternative and cultural methods (such as mowed ground cover and manual pruning of infested branches, respectively) that promoted high populations of both guilds. Unexpectedly, the structures of these communities were not related to the number of treatments, management of tree vigour or of the surrounding environment. The four strategies identified can be further interpreted as steps towards a redesign of orchard protection where integrated organic farming would be the most advanced stage. However, the paradox between effective protection strategy and biodiversity conservation still remains, casting doubts on the agroecological concept of sustainability