RHS warns of new Xylella fastidiosa plant disease
The quintessential UK garden, bursting with a wide variety of flowers, fruit and vegetables, could be lost to an unprecedented new disease. First flagged by the Royal Horticultural Society (RHS) in 2018, Xylella fastidiosa has hit the news once again as the UK clamps down on the importation of olive trees.
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.
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 RHS point out that the disease is difficult to identify and so there is the added problem that it could advance unnoticed. It is spread by insects including leafhoppers and froghoppers and infected plants will either show no symptoms or exhibit ones which may be confused with other common problems such as drought or frost damage such as leaf scorch, wilt, die-back and plant death.
If the disease does get into the UK, host plants within 100m could be destroyed and there would be restrictions on movement of plants within a 5km radius for five years – obviously causing considerable problems for surrounding nurseries and garden centres.
In addition,the UK government is also taking measures to tackle other threats to plants, including import controls on woods which may contain emerald ash borer.
Gardeners and the industry can 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.
The RHS has taken several steps over the last few years to mitigate the importation of the disease including:
Holding in isolation all imported semi-mature trees for at least 12 months prior to planting in RHS gardens and RHS shows wherever 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.”
Tom Attwood, of Cumbria based Abi & Tom’s Garden Plants, points out that sourcing locally from UK based nurseries growing their own stock will help reduce the risk: “The UK has no reported cases of Xylella and by relying on home-grown material ultimately mitigates the risk of an outbreak,” he said.
The Forestry Commission points out that Xylella fastidiosa, ‘affects its host plants by invading their water-conducting systems, moving both upstream and downstream. In so doing, it restricts or blocks the movement of water and nutrients through the plant’. Their website outlines the four known sub-species of the bacterium and its spread. Further information can be found here: https://www.forestry.gov.uk/forestry/beeh-a3vemx
A useful identification chart is available from: https://www.rhs.org.uk/science/pdf/plant-health/IPSN-Poster-Xylella-UK-garden-plants.pdf
DEFRA has also issued plant health guidance for UK for all plant growers, retailers, landscapers, garden designers, importers etc., and can be found by linking here.