Orchard characteristics, landscape factors, and management strategies influencing the spread of apple proliferation: epidemiological insights from cider orchards in Northern Spain

Abstract

Apple proliferation (AP) is one of the most severe diseases affecting apple trees in Europe, yet its epidemiology remains poorly documented in Spain. The spread of ‘Candidatus Phytoplasma mali’ may be influenced by insect vectors, landscape, and crop managements. To evaluate these factors, a regional-scale survey was conducted in Asturias (northwest Atlantic Spain), confirming the widespread presence of AP. Orchard age emerged as a key determinant of AP incidence and severity, while cultivar susceptibility also played a role, with ‘Regona’ exhibiting a higher infection rate than the set of six Protected Designation of Origin cultivars assessed in the study. Coniferous plantations were identified as a major driver of AP spread, increasing the likelihood of remigrant psyllids returning to nearby orchards. However, contrary to expectations, no clear relationship was observed between the area dedicated to apple cultivation and AP incidence. Late-winter mineral oil applications effectively reduced AP incidence, likely by repelling psyllids and deterring oviposition. Notably, smaller orchards, which applied fewer insecticides, exhibited higher AP incidence and severity, highlighting the need to reduce vector pressure through improved management. Rootstock selection significantly influenced AP dynamics, with M7 potentially contributing to increased disease incidence, particularly in high-density plantings. An integrated management strategy that accounts for landscape characteristics, vector control, crop management, and orchard design is essential to mitigating AP spread and ensuring the long-term sustainability of apple production.