The quintessential UK garden, bursting with a wide variety of flowers, fruit and vegetables, could be lost to an unprecedented new disease in 2018, warns the Royal Horticultural Society (RHS). Xylella fastidiosa – a bacterium which restricts water movement in plants resulting in eventual death – has already caused widespread devastation on the continent and threatens to arrive in the UK through the importation of infected plant material.

Unlike most pests and diseases which are plant-specific, Xylella affects more than 350 different plant species with garden favourites such as lavender, hebe, rosemary and flowering cherry at high risk because of their popularity, susceptibility to different strains of the disease and association with outbreaks on the continent.

The disease, which is spread by insects including leafhoppers and froghoppers is difficult to identify meaning it could advance unnoticed. Infected plants either show no symptoms or exhibit ones which may be confused with other common problems such as drought or frost damage. If found in the UK, all host plants within 100m would be destroyed and there would be restrictions on movement of plants within a 5km radius for five years – striking a death knell for surrounding nurseries and garden centres.

In light of the threat, the RHS is calling on gardeners and the industry to future proof gardens by purchasing host plants that are UK-sourced and grown – that is, propagated from seed in the UK or grown in the UK for a minimum of 12 months – maintaining varied plantings and reporting potential cases of Xylella to Defra.

To help mitigate the risk posed by Xylella, and other pest and diseases, the RHS is adopting six new principles that will guide its activity across gardens, shows and plant centres and hiring three new senior staff who will oversee plant health issues. Short term actions include:

  • Holding in isolation all imported semi-mature trees for at least 12 months prior to planting in RHS gardens and RHS shows where ever possible
  • Incorporating evaluation of plant health risk into judging criteria for gardens at RHS Shows
  • Wherever possible using UK grown and sourced plant material
  • Developing a central list of RHS-approved suppliers that meet specified plant health criteria


Gerard Clover, Head of Plant Health at the Royal Horticultural Society, said:Xylella is a game-changer for gardeners and the horticultural industry and it is vital that we understand its potential impact. Unusually, the disease threatens not just one host but hundreds of different types of garden plants and its impact has been felt dramatically in France, Spain and especially Italy where entire groves of ancient olive trees have been wiped out. The question for the UK is not ‘if’ but ‘when’ the UK will have its first outbreak of Xylella and the industry and public must be prepared for the far-reaching impact of it.”

For more information about Xylella and the RHS’s new plant health policies please visit



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