Xylella fastidiosa was once restricted to the Americas but was discovered near Lecce, Italy, in 2013. Since the initial outbreak it has invaded over 23,000 ha of olives in the Apulian Region of southern Italy, and is of great concern throughout the olive production areas of the Mediterranean basin. The study modelled control zones currently employed in Apulia, Italy, and found that increasing buffer widths decreased infection risk beyond the control zone but may not stop the spread completely. This was due to the ability of the disease-spreading insects to transport themselves between sites.

Lead author Dr Steven White, a Theoretical Ecologist at the Centre for Ecology & Hydrology, said the model indicates the importance of control strategies reducing the risk of the disease-spreading insects infecting healthy trees through the use of wider buffer zones. Dr White said, “At these early stages of Xylella fastidiosa invasion, little is known about the rates of spread of this terrible disease of olive trees and how best to control it. This is largely due to biological and environmental differences between where the strain is invading and where it has originated. “Based on current surveillance work in Apulia, Italy, we have constructed a simple mechanistic model which attempts to replicate the pattern of disease spread. Then, building upon this model, we investigated the efficacy of the buffer zone control programme. “In doing so, this work provides policy makers with scientific information about how the disease might progress and how the control strategies imposed by the European Union may reduce the risk of spread to the rest of Italy and beyond.” Co-author, Dr Daniel Chapman, a Plant Community Ecologist at the Centre for Ecology & Hydrology, said, “The emergence of novel invasive plant diseases such as Xylella fastidiosa in olives is an increasing threat. Our study shows that simple models can help to plan disease management strategies in the early stages of an epidemic. “Thanks to new funding from the European Union, we will be further developing the approach to provide specific guidance on surveillance, containment and even eradication of new outbreaks.”

The research, funded by the European Food Safety Authority (EFSA) and the Natural Environment Research Council (NERC), also recommends that while many aspects of the Xylella fastidiosa invasion remain uncertain and hinder forecasting, future studies should investigate quantification of the infection growth rate as well as short and long term distance dispersal.