What attacks horse chestnut: pests and diseases the sources name
A register of the leaf-mining moth, the bleeding canker bacterium, the leaf blotch fungus and the scale insect that Forest Research, the Woodland Trust and the Royal Horticultural Society tie to horse chestnut in Britain: which trees each row names, the status each source gives, 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 status details are on the linked pages. The sources are about the common or European horse chestnut (Aesculus hippocastanum) unless a row says otherwise. Forest Research says horse chestnut leaf miner does not affect sweet chestnut (Castanea), and the chestnut register is on the chestnut page.
The register
| Agent | What the sources record |
|---|---|
| Horse chestnut leaf miner, Cameraria ohridella. Full profile | Kind: Moth whose caterpillars feed inside the leaf Hosts: Forest Research says it feeds on the European horse chestnut and on other Aesculus species, never as heavily, including Japanese horse chestnut, red-flowering horse chestnut, Indian horse chestnut and red buckeye. It says the moth can occasionally attack Norway maple and sycamore, especially when planted close to a horse chestnut, and that it is not thought a significant threat to them. Where and status: Forest Research says it is present in much of England and Wales, with four reported sightings in Scotland. Forest Research heads the page reportable in Scotland, and its text says there is no requirement to report sightings to the plant health authorities. Season: Forest Research and the Royal Horticultural Society both say the blotches appear in summer, sometimes as early as June, starting in the lower crown. The Royal Horticultural Society gives June to September as the active months. |
| Bleeding canker, Pseudomonas syringae pv. aesculi. Full profile | Kind: Bacterial disease Hosts: Forest Research says it affects European horse chestnut in Great Britain, that trees of all ages are affected and can die, and that some recover and some appear resistant. The Woodland Trust says it can lead to the death of trees. Where and status: Forest Research says it is found in all parts of Great Britain. It is listed as not notifiable and the page says there is no need to report suspected cases. Season: No season given on the page read. |
| Leaf blotch, Phyllosticta paviae (also Guignardia aesculi) | Kind: Leaf fungus Hosts: Forest Research describes it as causing brown patches that can be confused with leaf miner marks, with a yellow border round parts of them and a more reddish-brown colour. It says a tree can have both at once. The Woodland Trust says horse chestnut may suffer from Guignardia, a genus of fungi that causes leaf blotch. Where and status: No status or distribution given on the pages read. |
| Horse chestnut scale | Kind: Scale insect Hosts: The Woodland Trust says horse chestnut may suffer from a horse chestnut scale insect. It gives no further detail. Where and status: No status given on the page read. |
| Leaf scorch | Kind: Water stress, not a pest Hosts: Forest Research says trees in urban areas can be badly affected by leaf scorch, especially with heavy traffic, compacted roots, spring drought or unusually high temperatures, and that scorched leaves are almost completely brown without any mines or halos. Where and status: Not applicable. |
How the sources describe the effects
Forest Research says that at high population densities the leaf miner caterpillars can destroy most of the leaf tissue on a tree, that research has shown up to 75% of the total leaf area attacked, and that the loss of leaf tissue reduces total carbon assimilation by at most an estimated 30 to 40 per cent over the growing season, because most of the damage comes late in the season. It says the effect is mostly aesthetic and does not significantly impair the general health of the tree, but that infestation reduces the weight of conkers and seedling germination and vigour. The Royal Horticultural Society says that by August most of the leaf area may be mined, giving the impression that the tree is dying although it will survive, and that heavily affected trees can drop leaves early.
Forest Research adds that the moth might worsen a decline triggered by other threats, among them bleeding canker, leaf blotch, leaf scorch and the damage from droughts and floods, and says trees with all of leaf miner, leaf blotch and bleeding canker have been seen. It names the long-term risk as a decline in horse chestnut numbers if landowners opt to replace them with other species.
Where the moth came from
Forest Research says the leaf miner was first observed in Macedonia, in northern Greece, in 1984, was reported in Austria in 1989, and was discovered in the London borough of Wimbledon in 2002, since when it has spread through England and Wales. The Royal Horticultural Society gives the same Wimbledon date for the first identification in Britain.
Who the sources say to report to
Forest Research takes leaf miner records from Scotland through TreeAlert for research and monitoring. The offices for each country are on the report a pest in the United Kingdom page.
Sources
- Forest Research, horse chestnut leaf miner (Cameraria ohridella) page, read October 9, 2026
- Forest Research, bleeding canker of horse chestnut page, read October 9, 2026
- Woodland Trust, British trees, horse chestnut, read October 9, 2026
- Royal Horticultural Society, horse chestnut leaf-mining moth advice page, read October 9, 2026