Bleeding canker threatens horse chestnut

I can’t walk past a horse chestnut tree without stopping to examine it.

I look for signs of disease, for the bleeding canker of horse chestnut. It’s a new disease and it’s virulent in western Europe. Thirty percent of horse chestnuts in the Netherlands, Germany, France and Belgium are likely infected. Fifty percent in Britain. I can’t find statistics for Ireland, but it’s bad here as well. The OPW is felling infected trees in Dublin’s Phoenix Park.

The first signs are a dark, tarry or rusty gum that exudes from the bark on the trunk or on infected limbs. The infection spreads and girdles the tree, which dies. This can take a while with a large tree and it’s the crown that dies back first. Occasionally, there is a spontaneous remission and the tree recovers. It was thought to be a fungal disease but it’s now known to be caused by a bacterium. There is no known cure, though possibilities are under trial. Horse chestnuts are magnificent trees, particularly when they’re in bloom, and it’s sad to think that if the disease becomes rampant the game of conkers may become extinct.