Horse Chestnut trees are under attack from a bacterium called Bleeding Canker, a disease that appears as a black tarry deposit on the trunk and branches that oozes out of the stem.
Chestnuts have long been known to suffer from a cankerous infection caused by the fungal-like Phytophthora. Around five years ago, however, a steep increase in the number of reports of bleeding canker prompted researchers to review earlier analysis. It was then realized that a new bacterium identified as Pseudomonas syringae pv aesculi had taken hold.
While it is still unclear how the disease spreads, it is thought that insect activity can spread the bacterium from tree to tree. Once that bacterium enters a tree, its effects can be catastrophic. The bacterium attacks and kills the bark, creating a wound. The tissue then becomes discoloured and extends, oozing a sticky tar substance that eventually takes on a hardened black varnish appearance.
Research in Austrailia and California suggests that the application of a Phosophite based material to the bark, stem and soil will strengthen the plants defense system, dry up the bleeding and arrest the advance of this disease. Phosphite treatments may also reduce the levels of new infestation.