Bleeding canker in horse chestnuts is a nationwide concern. We have been monitoring it in the borough since 2005 and have needed to remove several trees suffering from it.
What is it?
Horse chestnut trees are succumbing to an infection caused by the bacteria Pseudomonas syringae. The predominant symptom of the infection is a bleeding canker which are are lesions that ooze or "bleed" rusty red or black gummy liquid from the trunks or branches of trees.
The more lesions that appear on the trees the more patches of bark die. As the patches join together and extend around the trunk the vital ring of wood that supplies water and nutrients to the tree is destroyed. Once a significant area of the timber is dead, large branches in the crown of the tree split and die back and the vigour of the remaining crown begins to suffer.
Most decay in trees spread within the heartwood of the tree and show no outward signs of a problem until the decay is advanced. Specialist equipment is often needed to detect the internal decay and chart the decline. However the decline of a chestnut tree through bleeding canker is very visible.
Forestry Research, the advisory arm of the Forestry Commission, has done a lot of research and in their 2007 study of the condition found that 46% of the sample trees examined in the east of England region were infected, with urban trees affected more than rural ones. The bleeding canker is significantly impacting on the population of horse chestnuts across the country:
"In the case of horse chestnut, some trees eventually die, some recover and others have to be felled for safety reasons because the condition weakens the trunks or branches until they are in danger of falling."
For further information on the infection visit The Forestry Commission website.
How we are managing the condition
Our street tree survey shows we have 629 horse chestnuts in urban verges and, unfortunately, we have been seeing all the early signs of bleeding canker in a significant number of them over the last few years. We have followed the advice given by Forest Research on the progress of the infection. We have felled some of the infected trees in the past and it is likely that more horse chestnuts will need to be removed in the future.
The avenue of 30 horse chestnuts on Parkway have been badly affected. One tree was felled in 2006, five trees in 2011 and nine in 2013. In 2014 sweet gum (Liquidambar styraciflua) were been planted to replace those that were removed. We are monitoring the remaining horse chestnuts to assess their condition as they all are gradually declining. It is the intention to replace all the horse chestnuts with sweet gum to create a new avenue along the southern end of Parkway.
In Hatfield Hyde cemetery in Hollybush Lane all the horse chestnut trees are showing varying degrees of the infection and, sadly, seven trees were felled in 2011 and replaced with English oak.
What to do if you notice a horse chestnut tree with the infection
If you notice bleeding canker on your own horse chestnut trees we recommend that you contact a tree surgeon or tree specialist to advise you how to manage the problem.
Horse Chestnut Leaf Miner
This is another noticeable infection that Horse Chestnuts have been suffering from in recent years. All species of tree are attacked by insects, bacteria and fungi but in the last seven to eight years horse chestnuts have suffered heavily from attack by a moth known as Cameraria ohridella, the horse chestnut leaf miner. The larvae tunnel into leaves initially creating small brown patches. However, these spread rapidly across the entire tree, giving an autumnal appearance by late July or early August. Eventually, leaves die and fall prematurely. Current research indicated that this is mainly an aesthetic problem and does not affect the long term health of the trees.
More information can be found on The Forestry Commission website.