asked Her Majesty's Government:

What is the extent of the spread of bleeding canker (Phytopthora cactorum and P. citricola) in horse chestnut trees and other species in the United Kingdom; what is the extent of the threat of that disease to horse chestnut trees and other species; and what action they are taking against that threat. [HL5893]

Infection of horse chestnut trees by both Phytophthora cactorum and P. citricola is relatively uncommon and gives no cause for concern. It has also been recorded on lime. However, in recent years bleeding canker of horse chestnut has been more widely reported throughout the country and this is now known to be caused by a bacterial disease, Pseudomonus syringae pathovar aesculi, not previously recorded in this country.

Bleeding canker can sometimes kill its host, or it can weaken it until it becomes unsafe and needs to be felled. Some trees do show signs of remission, although it is not yet known if this leads to permanent recovery.

The Forestry Commission carried out a survey of 2,629 horse chestnut trees in 2007 to determine the extent and severity of symptoms of the disease. This showed that 49 per cent of all trees assessed displayed symptoms which could be caused by this new disease. A copy of the report has been placed in the Library of the House.

There is currently no known treatment against bleeding canker. The Forestry Commission is now testing whether healthy trees, growing in close proximity to infected specimens, have a degree of genetically inherited resistance which raises the possibility that these trees could form the basis of future generations.