Specific recommendations for the management of bleeding canker of horse chestnut

 

Our understanding about this disease is limited at present and this makes it difficult to make precise recommendations about the management of the disease and affected trees.  In these circumstances the following course of action is recommended until better information is available:

• Before embarking on any control measures on sites where there is a significant number of horse chestnuts, a survey to assess the number of affected trees is recommended (see surveying).
• Unless there is an immediate concern about safety, trees with light to moderate bleeding and vigorous crowns can be left in place and monitored.  Recovery may be possible and removal of trees which are still relatively vigorous (although diseased) may be premature.
• On sites where several horse chestnuts are present but only a few trees are affected, it is possible that removal of the diseased trees will reduce the risk of the healthy trees becoming infected.  Unfortunately, as we have no definite knowledge of how the pathogen is spread, there is no guarantee that such measures will be successful.  However, as small trees are more likely to succumb to the disease in the short term because they can be girdled in a shorter time than larger trees, the removal of young trees is therefore more easily justified than removal of large specimens.
• Trying to treat infected trees by pruning or cutting out infected bark, may be counterproductive - it may create wounds that allow new infections to establish and encourage the disease to spread.  Beneath the necrotic and dead bark of certain affected trees there are reservoirs of the bleed fluid which may contain inoculum of the pathogen.  Cutting diseased bark allows this fluid to be released which may be a source of infection.  In any case, if the areas of affected bark are either large or numerous, removing them by excision may create too much damage.
• Avoid disturbance around the trees, especially soil movement or applications of fertilisers.  This type of activity may lead to the spread of the disease to healthy trees and may even make the trees more susceptible to infection.
• If trees have to be treated, and pruning or felling is undertaken, start with the most lightly affected trees and progress towards the most heavily infected.
• Always disinfect tools after working on affected trees, and when moving from site to site.  Tools can be disinfected with methylated spirit, a solution of domestic bleach or one of the commercially available disinfectants.
• Where practicable, hose off machinery and vehicles that have been on infected sites, to reduce the likelihood of transferring the infection to new areas with horse chestnuts.
• Avoid bringing in young horse chestnuts to be planted on sites where the disease is absent, to minimise the risk of introducing the causal agent of bleeding canker.  Instead, consider establishing trees directly on site by planting conkers that come from horse chestnuts that are already growing there.