Horse Chestnut Canker, caused by the bacteria Pseudomonas syringae pv aesculi, is the most serious disease affecting trees in the Aesculus family.

• Infected Horse Chestnut Trees develop open, bleeding wounds on the bark that ooze a dark red-black fluid that tends to be clearer in Spring and more opaque by Autumn.
• If these grow all the way round, girdling the tree, it will die above that point.

The canker will attack trees of all ages and is most dangerous on trees in the age range up to 30 years old, after which their trunks get wide enough for girdling to be less likely.

It is not a guaranteed killer, some trees fight off the canker and recover.

Dealing with infected Horse Chestnut trees

There is no chemical cure, and we don’t even really understand how the bacteria are spread: wind, water, and insects are the possibilities, and perhaps all three.

Diseased trees are best dealt with by qualified tree surgeons.

• In order to stop the canker spreading, try not to prune or do other cutting work on infected trees.
• If you have to cut, immediately paint the wound with a pruning sealant such as Medo.
• If pruning is necessary, the tools must be disinfected in between trees. Use 9 parts methylated spirits to 1 part disinfectant cleaning agent, such as Jeyes Fluid.
• Do not disturb the surrounding soil.

Where you remove infected trees, do not replace them with more horse chestnuts: they are likely to get canker too.

Handling infected chestnut wood

Infected wood should be stored away from other horse chestnut trees, and covered up until you can burn it; don’t save it for firewood, or chip it.

If you can’t burn it yourself, take it to a green waste facility.