Increased proportion of exclusion netting in the landscape affects pest damage in unnetted apple orchards.
Abstract
The spatial distribution of agricultural practices in the landscape can affect pests through landscape concentration-dilution or resource limitation effects. Furthermore, these landscape effects could interact with the local impact of agricultural practices. In pome fruit orchards, exclusion nets are increasingly used, especially in organic orchards, to prevent damage from the codling moth (Cydia pomonella). However, their broader impact at the landscape scale, including potential effects on non-target pests like aphids, remains largely unexplored, as are interactions between local and landscape effects of agricultural practices. From 2021 to 2023, we investigated the effect of exclusion nets in organic farming on the target pest and two non-target aphid pests (rosy and woolly apple aphids, Dysaphis plantaginea and Eriosoma lanigerum) in the main apple production area of southern France. We monitored 23 pairs of organic orchards, each consisting of a netted orchard adjacent to an unnetted orchard, to disentangle the local effects of nets from those of nets in the surrounding landscape on local infestations by C. pomonella and the two aphid species. Locally, C. pomonella damage and diapausing larvae were reduced in the netted orchards. Unexpectedly, the probability of D. plantaginea presence was also reduced, but not that of E. lanigerum. Additionally, we observed some effects of the landscape-scale distribution of nets. Both the damage from C. pomonella and the presence of D. plantaginea increased in unnetted orchards when there was a high proportion of netted orchards in the surrounding landscape (only observed in 2021 for D. plantaginea). Damages from C. pomonella also decreased significantly, but only in unnetted orchards when there were more pome fruit orchards in the landscape. Synthesis and applications. This study is the first to reveal that nets significantly impact pest dynamics on the scale of agricultural landscapes. We recommend landscape-scale coordination in the deployment of nets, along with additional protective measures to mitigate their unintended effects on pests at the local and landscape scales.