Xylella: what the agencies record
What Forest Research, the UK Plant Health Information Portal and the European Food Safety Authority say about Xylella fastidiosa: the bacterium and its sub-species, the broadleaved trees it can infect, the insects that carry it, the leaf symptoms, the diseases that look like it, and where it is recorded.
Checked against the sources at the bottom of this page on October 8, 2026. Rules, fees and pay change: the source has the last word.
This page reports what the official source says. It is not legal advice: ask the office named here. It lists what the sources record about Xylella and does not diagnose any tree. Forest Research describes it as a quarantine organism, so it also states a reporting expectation for Great Britain and Northern Ireland, and the exact wording is on the pages linked below. The list of other diseases is on the tree diseases page, and the reporting lines are in the United Kingdom report-a-pest guide.
At a glance
| Item | What the sources say |
|---|---|
| Pathogen | Xylella fastidiosa, a bacterium. Forest Research says it has four known sub-species: multiplex, fastidiosa, pauca and sandyi. |
| Hosts | Forest Research names oak, elm, plane and maple among broadleaved trees, and grape, citrus, coffee, olive, almond and blueberry among crops. The European Food Safety Authority database lists 696 plant species from 88 botanical families, and says not every plant listed is susceptible to every sub-species. |
| Where | Forest Research says outside trade premises it has been found in France, Spain, Italy, the Americas and Taiwan. The UK Plant Health Information Portal, last updated December 17, 2025, lists outbreaks in France, Italy, Spain and Portugal. |
| Status in the United Kingdom | Not known to occur there. Forest Research says an infected imported plant has been intercepted, and lists it as notifiable. |
| Report to | Great Britain: TreeAlert. Northern Ireland: TreeCheck. Trade premises: the country plant health authority. See the United Kingdom guide. |
How the sources say it spreads
Forest Research says that in nature the bacteria are carried only by insects from the Cicadellidae and Cercopidae families that feed on xylem fluid, the water-carrying vessels of the plant. It names the common froghopper as a UK species that could act as a carrier, says these insects usually fly up to 100 metres but can be blown much farther, and says some transfer between neighbouring plants through root grafts. It lists movement of infected plants for planting as the route for long-distance spread. The European Food Safety Authority says sharpshooters and spittlebugs are the vectors and that the bacteria block the xylem, which causes shortages of water and minerals in the plant. The UK Plant Health Information Portal calls imported host plants for planting the most likely pathway into the United Kingdom.
Symptoms as the sources state them
- General. Forest Research says symptoms range from leaf scorch, or browning, to dieback and death, and vary with the host and how susceptible it is. The European Food Safety Authority says many infected hosts may show no symptoms at all.
- Plane, maple, oak and elm. Forest Research lists leaf scorch, sometimes with dieback of twigs and branches. It says the leaf symptoms visible in summer include browning at the leaf margins but not along the main veins, often with a yellow edge to the browned area.
- Season. The only season Forest Research gives is summer, for the leaf margin browning above.
Look-alikes
Forest Research says several other problems cause similar symptoms: Dutch elm disease on elm, anthracnose and powdery mildew on plane, leaf blotch of horse chestnut, and browning from horse chestnut leaf miner, which browns the leaf between the veins instead of at the margin. It advises checking those first when affected trees are horse chestnut, plane or elm. Read the Dutch elm disease page for the elm one.
Sub-species named by the sources
Forest Research says sub-species multiplex can infect probably the widest range of hosts, including pedunculate oak, wych elm, plane and northern red oak. The UK Plant Health Information Portal calls multiplex the one of most concern to the United Kingdom, because it survives in cooler climates, and says pauca, which damages olive production in southern Italy, is unlikely to thrive in the United Kingdom. The European Food Safety Authority says the bacterium was first detected in the European Union on olives in Puglia, Italy, in October 2013.
What the agencies publish for control
Forest Research describes a strategy that aims to keep the bacterium out and to require pre-notification of host plants such as plane, elm and oak plants landing in the United Kingdom, so they can be inspected. The UK Plant Health Information Portal says eradication measures for an outbreak are set out in a contingency plan. The European Food Safety Authority says certain treatments in Apulia reduced symptoms but did not remove the pathogen from infected plants. Who may apply pesticides is covered on the pesticide licences page.
Credit
The Forest Research and UK Plant Health Information Portal material was read under the Open Government Licence v3.0 and is restated here in our own words.