Bleeding canker of horse chestnut: what the agencies record

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 bleeding canker of horse chestnut and does not diagnose any tree. The sources do not agree on reporting: Forest Research lists the disease as not notifiable, while the Woodland Trust page points readers to TreeAlert and TreeCheck. 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
Cause	Forest Research says that in most cases diagnosed since the year 2000 the cause has been the bacterium Pseudomonas syringae pathovar aesculi. The Royal Horticultural Society adds that two Phytophthora species, which are fungus-like organisms, more rarely cause the same kind of canker.
Hosts	Horse chestnut. Forest Research names European horse chestnut (Aesculus hippocastanum). The Royal Horticultural Society names the white-flowered tree and the red A. x carnea.
Where	Forest Research says all parts of Great Britain. The Woodland Trust says the origin is thought to be India.
Status	Present in the United Kingdom. Forest Research marks it not notifiable and says there is no need to report suspected cases to it.
Report to	Optional. The Woodland Trust names TreeAlert for Britain and TreeCheck for Northern Ireland. See the United Kingdom guide.

How the sources say it spreads

The Royal Horticultural Society says research on the bacterium was in progress at the page read on October 8, 2026. It says the bacterium may need wounds to infect, which may include the natural pores in the bark called lenticels, or might live on plant surfaces and move in wind-blown rain, and that Phytophthora, a related group of organisms, moves by similar routes and also makes resting spores that persist in soil. The Woodland Trust says the bacteria multiply in the water-carrying tissue just under the bark and eventually block it. Forest Research notes the disease went from four reported cases in 2000 to more than 110 reports in 2006.

Symptoms as the sources state them

Spring. Forest Research says bleeding patches release a dark but transparent liquid.
Summer. The liquid turns cloudy or opaque rusty-colored and runs down the trunk. In dry summer conditions the bleeding may stop and leave a dark brittle crust.
Autumn. Forest Research says renewed bleeding is often seen later in the year, which it reads as pathogen activity being greatest in moist, mild spring and autumn conditions. The Royal Horticultural Society says cankers can be seen at any time of year, and the Woodland Trust says the bleeds can dry out in winter.
Inside. Forest Research says the inner bark under the patches is usually dead, orange-brown and mottled, with wood sometimes stained blue-black. The Royal Horticultural Society says healthy inner bark is white or pinkish, and that the edge of the discoloured area is diffuse when infection is still spreading and sharply defined when it is stable.
Crown. Forest Research says that over several years the dead patches can join and encircle the trunk or a branch, and crown symptoms such as yellowing, early leaf drop and crown death follow. The Woodland Trust says some infections last for years with little effect on the crown.

Look-alikes and confirming the cause

Forest Research says similar symptoms can occur on other tree species, caused by different pathogens. It names Phytophthora root disease, where lesions run up to 1 to 3 m up the trunk from an infected root collar, and says honey fungus (Armillaria) can cause stem bleeding that is usually confined to the root collar and lower stem. It also says white fungal growth under dying bark is usually decay fungi arriving after the original cause, in which case the original agent cannot be isolated. Its management page says confirming the cause is critical to any recommendation. The same Phytophthora species cause bleeding cankers on lime in the UK, per Forest Research, and the Royal Horticultural Society has a separate page for them.

Survey results

Forest Research reports a 2007 Forestry Commission survey in which 49% of all horse chestnuts assessed showed symptoms to some degree, with rates that varied by region. The Woodland Trust gives 36% in Wales and 76% in South East England from the same year, which it calls the last survey for the disease.

What the agencies publish for management

Forest Research says no chemical treatment is registered or approved in the UK to cure or arrest the disease. Its management page lists a survey of affected trees, monitoring of trees with light to moderate bleeding and vigorous crowns, avoiding pruning or cutting out infected bark, working from the least affected trees to the most affected, disinfecting tools and machinery between sites, destroying felled material on site rather than chipping it, and not keeping logs from diseased trees. It does not recommend replanting with the same species. It says some trees survive for many years or recover through callus growth at canker margins. The Royal Horticultural Society says there is no chemical control available. Who may apply pesticides is covered on the pesticide licences page, and a related oak bleeding disease is on the acute oak decline page.

Credit

The Forest Research material was read under the Open Government Licence v3.0 and is restated here in our own words.