This disease has been found mainly on Horse Chestnut trees and in severe cases can lead to death. It was earlier thought to be a symptom of Phytophthora fungal infections, but the bacterium Pseudomonas syringae pv aesculi has been identified as the causal agent. Recently the DNA of the bacterium has been sequenced and this gives a clue to its origin and development. It is believed that it is a more virulent strain of the same bacterium that occurs in India, attacking the Indian horse chestnut, but only causes lesions on the leaves. The European strain has some additional genetic material and lives off the sugars in the sap. Knowing the genetic makeup may help to derive better methods to control it.
On affected trees sap can be seen oozing from the bark and running down the trunk. The bark becomes cracked and distorted, and on smaller trees complete girdling leads to death. If the weeping sap is removed and the cankers pared away they may dry up and heal.
A new treatment called Conquer is being launched for aboriculturalists to use. It is prepared from garlic, Allium sativum and is injected via a series of plug holes around the tree to be taken into the vascular system where it can act on the infection. It takes about a year for the tree to recover. Recent trial results have been promising, and some have reported that the treatment has an effect on the leaf miner which is also attacking the chestnut trees.
Other bleeding cankers caused by Phytophthora fungi, P. cambivora and P. citricola can be found in other tree species. Another, P. alni affects Alder trees. The spores are carried in water and resting spores can be found in soil.
Slime Flux or Bacterial Wetwood is another disease which causes oozing from the trunk that is usually an orangey colour with a foul smell.
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