Acute oak decline: 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 Forest Research records about acute oak decline and does not diagnose any tree. Forest Research lists the disease as reportable in the United Kingdom, which is a request for reports and not a legal duty. The list of other diseases is on the tree diseases page.

At a glance

Item	What Forest Research says
Causal agent	There is no single causal agent. The lesions are caused by a mix of bacteria. Three are found in abundance: Brenneria goodwinii, Gibbsiella quercinecans and Rahnella victoriana.
Hosts	Mainly pedunculate and sessile oak. Other oaks listed include holm, Turkey, red, scarlet, pin and water oak.
Where	Found mostly in south-eastern, central and eastern England and the Welsh Borders and south-east Wales. As of 2020 it had not been reported in Scotland or Northern Ireland.
Status	Present in the United Kingdom and reportable.
Report to	Great Britain: TreeAlert. Northern Ireland: TreeCheck. See the United Kingdom report-a-pest guide.

What Forest Research calls it

The page calls acute oak decline an emerging disease first observed in the UK late in the 20th century, which can kill oaks within four to six years of the first symptoms. It says most affected trees have been mature specimens more than 50 years old, though affected younger trees with trunks 10 to 12 cm across have been recorded. It says the trees likely need to be weakened first by factors such as environmental ones, and describes the disease as present in warm, drought-prone parts of the UK with high airborne nitrogen pollution. It describes the incidence work as defined in 2008 and 2009 in Britain, with photographs and descriptions available from 2006 onward.

Symptoms as the source states them

Stem bleeds. Dark, vertical, weeping splits in the bark, which seep black fluid between the bark plates and down the trunk. The splits are typically 5 to 10 cm long and usually first show 1 to 2 meters above the ground. Beginning in spring the fluid runs down the stem and stains the bark.
Dry periods. The page says bleeding often stops at certain times of the year, leaving dry black streaks and crusts.
Under the bark. A wet, slimy lesion forms beneath the outer bark, and the tissue breaks down into a fluid-filled cavity.
Beetle signs. D-shaped exit holes of the two-spotted oak buprestid, about 4 mm wide and 3 mm high, occur in about a third of cases, with larval galleries often under the lesions. Forest Research says the beetle is not considered a cause but is thought to be opportunistic on weakened trees.
Crown. The canopy may thin as the tree nears death, and symptoms can develop over 18 months. The symptoms page says deterioration in the crown often does not occur until the tree is near death.

Look-alikes and lab confirmation

Forest Research says weeping patches or stem bleeds are a common response by trees to attack from pests and pathogens, for example Phytophthora species, so a stem bleed alone does not necessarily indicate acute oak decline. It says checking reports was labor-intensive at first and has been sped up with a rapid diagnostic tool that detects the bacteria. It holds a database of symptomatic oaks reported to its Tree Health Diagnostic and Advisory Service and collates the confirmed reports.

Where reports are confirmed

The incidence page says the map of confirmed sites from 2006 to 2024 shows the disease mainly in England, with particular prevalence in the London area, the South East and East Anglia, the furthest north being around Delamere and Mansfield. It reports increasing occurrences along the Welsh borders and none in Scotland. A separate probability map based on temperature, rainfall and atmospheric nitrogen shows where it would be expected.

What the agency publishes for management

Forest Research says there is no cure and that its guidance is based on general biosecurity principles meant to reduce the risk of moving the bacteria from affected to healthy trees. Its advice page says its understanding of the cause is limited. In general terms, it recommends recording the number and location of symptomatic trees, leaving affected trees in place and monitoring them unless there is an immediate safety concern, and avoiding contact with the bleeds. It says pruning infected trees is discouraged, that where only a few trees on a site are affected felling and destroying them may be prudent, and that parts of infected trees should not be used for mulch or compost. It also lists precautions for felling and for moving wood, which the page itself sets out. It says management that targets soil health may help support declining oaks.

Credit

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