What attacks chestnut: pests and diseases the sources name
A register of the blight fungus, the gall wasp, the borer and the root-attacking water moulds that British and Canadian sources tie to chestnut: which chestnuts each page names, where each is recorded, the season each source mentions, and where the full profile is.
Checked against the sources at the bottom of this page on October 9, 2026. Rules, fees and pay change: the source has the last word.
This page reports what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. Each row names its source, all read on October 9, 2026. Where this site has a full profile, the row links it, and the regulated status tables are on the linked pages and are not repeated here. The record for the chestnut grown in Britain is on the sweet chestnut page. Horse chestnut is a different tree, in a different genus, and Forest Research says neither the blight nor the gall wasp attacks it.
The register
| Agent | What the sources record |
|---|---|
| Sweet chestnut blight, Cryphonectria parasitica. Full profile | Kind: Fungus Hosts: Forest Research says it is usually fatal to European and American chestnut, and that European chestnut might be less susceptible than the American. It says the fungus can occasionally affect some oaks standing very close to heavily infected chestnut, with cankers on oaks tending to be superficial. Where and status: Forest Research lists it as present in the United Kingdom and notifiable, found at a number of sites since 2011, principally in central and southern England. Season: Forest Research says orange fruiting bodies exude spore tendrils in moist weather, and leaves above a girdling canker wilt and turn brown but stay hanging on the tree. |
| Oriental chestnut gall wasp, Dryocosmus kuriphilus | Kind: Gall wasp. Forest Research says it does not need males to reproduce Hosts: Forest Research says it affects European, American, Japanese and Chinese chestnut and their hybrids, and does not attack horse chestnut. Where and status: Forest Research lists it as present in the United Kingdom and notifiable, first found in Farningham Wood, Kent, in June 2015 and shortly afterwards in street trees in St Albans, with most later sites in and around London and south-east England. It is established in several European countries from Germany and the Czech Republic to the Mediterranean. Season: Forest Research says the galls form in early summer and the adult wasps emerge from them in June and July. |
| Twolined chestnut borer, Agrilus bilineatus. Full profile | Kind: Wood-boring beetle, a secondary pest Hosts: Natural Resources Canada says it attacks several oaks and American chestnut, and that in Canada it is most often found on weakened red, white and bur oak. It says English oak is known to be highly susceptible, and that 2018 finds of the beetle in Turkey raise concern for European chestnuts and oaks. Where and status: Native to North America east of the 100th meridian, from Manitoba to New Brunswick and the eastern United States. No regulated status is given. Season: Peak adult emergence from June to July. Wilted foliage on scattered branches in late summer is the first symptom of established galleries. |
| Phytophthora root rots, mainly P. cinnamomi and P. cambivora. Full profile | Kind: Water moulds that attack roots Hosts: Forest Research says sweet chestnut is susceptible to several root-attacking Phytophthora species. Where and status: Britain, in the species entry. No regulated status is given for these two. Season: No season given on the page read. |
How the sources describe the effects
Forest Research says blight infection usually kills the tree, with fungus entering through fissures or wounds in the bark and spreading fast enough to girdle stems or branches. It says the loss in Europe has not matched North America, where the disease almost wiped out the chestnut population, but that tree losses have been regionally significant. It adds that sweet chestnut woodland amounts to about 2 per cent of England's wood cover, most of it in southern England, so any impact would be regional. On the wasp, it says the galls on buds, leaves and leaf stalks can weaken trees in high numbers and make them more vulnerable to other pests and diseases, especially blight, and that severe attacks can cause decline.
Natural Resources Canada calls the twolined chestnut borer a secondary pest that only succeeds on trees stressed by drought or earlier defoliation, but says trees can be killed in the first year of attack if their health is already poor.
Profiles on this site
The full profiles linked in the table are sweet chestnut blight, twolined chestnut borer and Phytophthora root rots. The Oriental chestnut gall wasp has only the row above, because the text read gives too few separate facts for a page of its own.
Who the sources say to report to
Forest Research asks that suspected sweet chestnut blight and suspected Oriental chestnut gall wasp in Great Britain be reported through TreeAlert. The page read for the borer names no report line. The reporting offices for each country are on the report a pest in the United Kingdom and report a pest in Canada pages.
Sources
- Forest Research, Sweet chestnut blight (Cryphonectria parasitica) page, read October 9, 2026
- Forest Research, Oriental chestnut gall wasp (Dryocosmus kuriphilus) page, read October 9, 2026
- Forest Research, tree species database entry for sweet chestnut (SC), read October 9, 2026
- Natural Resources Canada, Twolined chestnut borer fact sheet (revision 2025), read October 9, 2026