Symptoms of bark death with associated stem bleeding are not indicative of a particular disease or just confined to horse chestnut. Many tree species, including horse chestnut, may suffer from Phytophthora root disease, particularly on sites that are liable to be wet. In these instances Phytophthora infects the roots and root collar but the lesions may extend upwards by as much as 1-3m and be visible as bleeding areas on the tree trunk. This type of stem lesion, connected to a root infection, is distinct from the isolated aerial lesions that have been found to be caused by P. cactorum and P. citricola on horse chestnut in the past (Brasier and Strouts, 1976).
Other species that have shown symptoms of bleeding canker
Apart from horse chestnut, bleeding canker caused by P. cactorum and P. citricola has also been recorded on lime (Tilia). In the USA, the same pathogens have also been found (Strouts, 1981) to cause bleeding cankers on:
- Acer (maple)
- Betula (birch)
- Liquidambar (sweet gum)
- Quercus (oak)
- Salix (willow).
Recently, diagnosing the major cause of bleeding cankers on horse chestnut has also been complicated by the appearance of a new pathogen known as Phytophthora ramorum, which is the cause of Sudden Oak Death in the USA. Further detailed information about P. ramorum:
- Forestry Commission pages about P. ramorum
- Department of Environment Food and Rural Affairs (Defra)
- Risk Analysis for P. ramorum (RAPRA)
Phytophthora ramorum in the UK
P. ramorum has been found mainly in nurseries in the UK and is now listed under emergency EC plant health legislation. In a few instances P. ramorum has been found to cause bleeding cankers on certain broadleaf species in England (Brasier et al. 2004), including a single specimen of horse chestnut.
Only about thirty trees have been affected in this way, and most have been located in Cornwall (See www.forestry.gov.uk/pramorum). In all cases, such trees have been found close to rhododendrons which have foliage infected with P. ramorum; these have probably been the source of the disease for the trees. See:
Path Bulletin (Path News) 6 - Dec 2003 (PDF-292K)
In addition, the climate in the areas where P. ramorum has infected trees is mild, influenced by the nearby coast, with moisture laden winds. This has probably helped to spread spores of P. ramorum and increased opportunities for infection. The majority of affected trees have been beech trees (Fagus sylvatica).
Unless a horse chestnut with bleeding cankers is in a location where a source of P. ramorum (such as infected rhododendrons) is nearby, then the likelihood of infection by P. ramorum is negligible. Instead, the bleeding canker will have been caused by another pathogen.
However, if it is suspected that a tree is suffering from a disease caused by a quarantine organism such as P. ramorum then inform:
Plant Health Branch
Tel: 0131 314 6414
Or email email@example.com