Xylella fastidiosa is a bacterium that causes leaf scorch, wilting, dieback and death in a very wide range of plants. Since 2013 it has killed millions of olive trees in southern Italy, and there are major outbreaks on ornamental plants in southern France and Spain's Balearic Islands, and more recently Portugal. It has not been detected in the UK. For a home gardener there is no treatment to learn, so what matters is knowing what it looks like, why treating it yourself would be the wrong move, and who to tell.
Current status: not detected in the UK
Xylella fastidiosa has not been detected in the UK, Scotland included. It is a GB quarantine pest, prohibited from being introduced into or spread within Great Britain, so a suspected case brings a formal containment response, not a garden treatment.
An olive orchard near Gallipoli in Puglia, Italy, where the outbreak is real. It is not a UK or Scottish scene.
Plants to know
The host range is very broad. Nine plants are rated high-risk hosts in the UK, among them rosemary, lavender, olive and cherry (with other Prunus), and blueberries are among the other important hosts. None has been found infected in Scotland; these are the plants to watch if the position changed.
What it looks like
Leaf scorch, wilting, dieback and eventual plant death are the symptoms. Drought, frost and many ordinary diseases cause the same signs, so symptoms alone don't identify it, and a laboratory test is what confirms it.
It spreads two ways. Locally, insects that feed on plant sap pick the bacterium up from an infected plant and carry it to the next one they feed on; the meadow froghopper or meadow spittlebug (the insect behind cuckoo spit) is the most notable vector in the UK, and the insects do no damage themselves. Over longer distances it spreads when infected plants are moved in trade. Imports through professional routes are inspected and documented, and the risk of undetected infection is likely to be higher for a plant brought back in a passenger's luggage.
Why this matters in Scotland
The bacterium isn't in Scotland, and Scotland is preparing in case it arrives. SASA, the Scottish Government's plant health agency, runs routine surveillance on plants in trade and has been collecting spittlebugs across Scotland and recording which plants they live and feed on. A Plant Health Centre project in 2021 to 2022 modelled where the insects that carry the bacterium occur, and how abundant they are, across Scottish landscapes, ahead of any detection.
A suspected case in Scotland can be reported directly to the Scottish Government's Horticulture and Marketing Unit ([email protected]) as well as through the UK-wide portal.
What happens if it is found
The response depends on how early it is caught. If infection is found at an early stage and is not thought to have spread, the infected plant and host plants close by are destroyed, and plants and insect vectors within 200m are surveyed for a minimum of two years. If it is thought to have spread, host plants within 100m are destroyed, a 2.5km buffer zone has restricted movement, only specified plants can be replanted for at least four years after the last finding, and the insects that spread it are controlled. The earlier it is caught, the smaller the response.
What to do
There is no product or technique that fixes an infected plant. Two things are within a gardener's control.
Report a suspected case, do not attempt to treat it yourself
Compile the host plant name, symptoms, origin and import history, and report to the UK Plant Health Information Portal, or in Scotland directly to the Scottish Government's Horticulture and Marketing Unit at [email protected]. Do not send plant samples to RHS.
Favour UK-grown or long-established plants over recently imported stock, especially for priority hosts like rosemary, lavender and olive
UK-grown plants and seeds pose a very low risk, and a plant established in your garden for more than five years that has been healthy is also low risk. Spread over long distances happens when infected plants are moved in trade, and a plant brought back in a passenger's luggage is more likely to carry undetected infection than one that came through a professional import route.
Myths about Xylella fastidiosa
“Xylella fastidiosa has already turned up in UK gardens, so it's too late to worry about keeping it out”
The bacterium has not been detected anywhere in the UK, including Scotland. It's classed as a GB quarantine pest, meaning it is legally prohibited from being introduced or spread here, a status that only applies to something the authorities are actively keeping out, not something already established. Scotland does not treat the absence as permanent: SASA runs routine surveillance on plants in trade, and a Plant Health Centre project has modelled where the insect vectors occur.
What to do: Treat unexplained wilting, scorch or dieback on a known host plant, especially rosemary, lavender, cherry or blueberry, as worth reporting rather than dismissing.
In Scotland: SASA has been collecting spittlebugs across Scotland and recording the plants they feed on, and a 2021 to 2022 Plant Health Centre project modelled vector occurrence and abundance across the Scottish landscape.
2 sources
- RHS: Xylella fastidiosaXylella fastidiosa has not been detected in the UK, though there are serious concerns about its introduction via imported plants.
- Scottish Government: Plant pests and disease guide, Xylella fastidiosaXylella fastidiosa is a GB quarantine pest, prohibited from being introduced into or spread within Great Britain.
“Xylella fastidiosa is purely a border-control and import-licensing problem, so there's nothing an individual gardener can do about it”
A gardener controls two things: what they buy, favouring UK-grown or long-established plants over recently imported stock in host species, and what they do if they suspect a case, which is to compile the plant, symptoms, origin and import history and report it rather than staying silent. A case caught early means a smaller destruction zone and survey area than one that has already spread, so prompt reporting has a real effect on the scale of the response.
What to do: Choose UK-grown stock where it's a realistic option for rosemary, lavender, cherry, blueberry and similar hosts, and if you ever see leaf scorch, wilting or dieback that doesn't fit drought or frost, report it rather than trying to diagnose or treat it yourself.
2 sources
- RHS: Xylella fastidiosaUK-grown or long-established plants are rated low risk against imported stock, and suspected cases should be reported with plant, symptom, origin and import details rather than sent to RHS or treated at home.
- Scottish Government: Plant pests and disease guide, Xylella fastidiosaSuspected cases should be reported to the Scottish Government's Horticulture and Marketing Unit.
“If a host plant shows scorch or dieback, pruning out the affected growth can save it from Xylella fastidiosa”
A suspected case should not be controlled by the gardener at all: not pruned, not treated, not managed at home. The bacterium is moved from plant to plant by sap-feeding insects, so cutting out a shoot is unlikely to remove it. Gardeners are advised not to attempt any treatment, and the response to a confirmed case is destruction of the infected plant and nearby hosts by plant health authorities, alongside movement restrictions and control of the insects that spread it.
What to do: Don't prune, spray or otherwise try to manage a plant you suspect has Xylella. Report it with the plant name, symptoms and any import history, and let plant health authorities take samples and decide next steps.
1 source
- RHS: Xylella fastidiosaIf Xylella is suspected you should not attempt to control the disease yourself; samples should not be sent to the RHS, and containment through destruction and movement restriction is carried out by plant health authorities.
“Buying rosemary, lavender or a cherry tree from a UK garden centre means it can't be carrying Xylella”
Risk is graded by where and how a plant was grown, not by which shop it was bought in: UK-grown plants and seeds are rated very low risk, and a plant that's been established in a garden for more than five years and has stayed healthy is also low risk. A plant sold by a UK retailer can still have been grown abroad and imported recently, which is the higher-risk category, so the country the shop trades in doesn't by itself tell you the plant's growing history.
Our read The claim assumes that where a plant is sold settles the risk, while the risk criteria measure where it was grown and how long it has been in place. A UK-grown plant is rated very low risk, so the claim may often be right in practice, but a UK shop sign is not what makes it so.
What to do: For priority hosts like rosemary, lavender, cherry, blueberry or olive, ask where and how long a plant has been grown rather than assuming a UK point of sale settles the question, and favour clearly UK-grown or long-established stock when it's offered.
1 source
- RHS: Xylella fastidiosaUK-grown plants or seeds pose a very low risk, as do plants established in a garden for more than five years and previously healthy; imported plants carry higher risk.
“Scotland's cold, wet climate means Xylella fastidiosa could never really establish here even if an infected plant slipped through border checks.”
Peer-reviewed climate-suitability modelling of Xylella fastidiosa across Europe found its potential distribution is limited by minimum winter temperatures, and that fewer models predicted its presence in the northern part of France, the British Isles, Belgium and the Netherlands. That points towards cold winters limiting establishment. It is a continental model, though, and does not settle what would happen in a Scottish setting. The Defra portal adds that the subspecies that attacks olive is considered unlikely to thrive in the UK, while another subspecies has a wide host range that includes oak.
Our read The direction of the evidence is reassuring, but no study of Scotland's climate and vector species was found, so treating Scotland as safe by extrapolation would overstate it. It is a plausible hope, not a demonstrated fact.
What to do: Don't treat a cool climate as a safety net: buy host plants (lavender, rosemary, olive, cherry) from reputable suppliers and report unexplained scorch or dieback.
In Scotland: No Scotland-specific establishment study was found, so this is an open question rather than a settled one either way.
2 sources
- Xylella fastidiosa: climate suitability of European continent (Scientific Reports / Nature, peer-reviewed)The potential distribution of the three subspecies of Xf studied here appeared to be limited by minimum winter temperatures. The agreement between algorithms x climate datasets was somewhat lower in the northern part of France, the British Islands, Belgium and Netherlands where a lower proportion of models predicted the presence of Xf subsp. fastidiosa.
- Defra UK Plant Health Portal: Xylella fastidiosaThe pauca subspecies shows a preference for olive and is considered unlikely to thrive in the UK; the multiplex subspecies affects a wide range of hosts, including many native broadleaved trees such as oak.
Frequently asked questions
Is Xylella fastidiosa in Scotland?
No. It has not been detected in Scotland or anywhere else in the UK. It is a GB quarantine pest, prohibited from being introduced into or spread within Great Britain, and a suspected case is handled by the plant health authorities rather than left to a gardener to judge.
What should I do if I think a plant has it?
Don’t try to treat it, and don’t send a sample to the RHS, which does not test for it. Note the plant’s name, the symptoms, where it came from and its import history if you know it, then report it through the UK Plant Health Information Portal or, in Scotland, to the Scottish Government’s Horticulture and Marketing Unit at [email protected]. The earlier it is reported, the smaller the destruction zone and survey area.
Is there any treatment?
Not for a gardener. The advice is not to attempt to control it yourself. The response to a finding is regulatory: destroying infected and nearby host plants, restricting movement and controlling the insects that spread it. What a gardener can do is report a suspected case promptly and favour UK-grown or long-established plants.
Should I be worried about my rosemary, lavender, cherry or blueberries?
Not at the moment. These are among the plants Xylella can infect, but the bacterium has not been detected in the UK, so there is no current infection to act on. The practical steps for these plants are to buy UK-grown stock where you can, and to report unexplained scorch or dieback rather than treating it yourself.
Sources
Show the 6 sources
- RHS: symptoms, high-risk and other important hosts, insect-vector and trade-based spread, UK detection status, passenger-luggage import risk, interception and outbreak containment measures (200m survey, 100m destruction, 2.5km buffer, four-year replanting rule), reporting protocol, low risk for UK-grown and long-established plants
- Scottish Government: Scotland's own reporting route via the Horticulture and Marketing Unit, and GB quarantine pest status
- Plant Health Centre (James Hutton Institute): Scottish project (March 2021 to January 2022) modelling vector occurrence and abundance in the wider landscape; states Xylella has not been detected in Scotland or the UK
- Review of the Apulia outbreak (PMC): the outbreak identified in Europe in 2013 and the statement that it has killed millions of olive trees in Apulia, southern Italy
- SASA: not known to occur in the UK; concern about introduction on imported plants; routine surveillance on plants in trade; spittlebug collecting across Scotland; meadow spittlebug as the notable UK vector, which does no damage itself
- Defra Plant Health Portal: subspecies pauca (olive) considered unlikely to thrive in the UK, subspecies multiplex with a wide host range including oak; cherry, almond and lavender named in outbreak areas; infected plants for planting as the most likely pathway