Bleeding Canker & Sudden Oak Death

Many of our customers at Nicholsons have made enquiries on how some of the so-called "new tree diseases", such as "Bleeding Canker" and "Sudden Oak Death", have impacted on the local tree population in and around Oxfordshire.

We have also discovered during our Duty of Care tree surveys and subsequent tree surgery work just how badly these diseases are affecting our client’s trees. In response to these enquiries and concerns we have gathered together our best knowledge on some of the worst of these diseases: Bleeding Canker of Horse Chestnut, Sudden Oak Death and Oak Decline.

Bleeding Canker of Horse Chestnut

Until around the turn of the Millennium, bleeding cankers on Horse Chestnuts, Aesculus hippocastanum and related species, were a rare occurrence. Since then the incidence of the disease has rapidly increased to the point that the planting Horse Chestnuts is now equally as rare.

At first the disease was thought to be caused by a Phytophthora, a fungal pathogen. However research by Dutch scientists has since confirmed that it is in fact caused by a bacterium, Pseudomonas syringae.

Initial symptoms include bleeding areas on the stems and sometimes branches. The bleeding often takes the form of rusty red or brown exudates, as illustrated here, in our main picture, and also (close-up) in the title graphic.

Later this can develop into brownish gummy liquid that sometimes solidifies to form a crusty deposit.

After some months the area around the bleeding patch can crack. Over some years the dead phloem and cambium layers underneath can extend around the trunk resulting in yellowing foliage and eventually crown death. As the bark has been killed the tree becomes liable to attack from wood rotting fungi and this can have an impact on tree safety. Horse Chestnut is already infamous for being liable to ‘sudden branch drop’, but the canker makes this phenomenon more likely to occur.

Where trees are in areas with frequent public access then particular care should be taken to ensure that trees are inspected regularly. Nicholsons is able to carry out ‘Duty of Care Tree Surveys’ and in particular roadside tree surveys, as well as providing a full tree surgery contracting service.

Unfortunately there is no cure for the disease at the present time. As the future for Horse Chestnuts looks bleak, Nicholsons have taken the decision not to recommend the planting of Horse Chestnut until more is known about the disease or until resistant strains of the tree are discovered.

Our main picture (above) shows a young Horse Chestnut tree which is displaying some of the typical early symptoms, including bark necroses and bleeding exudates from the bark. There is also quite a lot of crown death but this is not easily visible during the winter when this photograph was taken.

Sudden Oak Death

This is primarily a shoot and leaf disease of shrubs, particularly Rhododendron, and in the UK is mainly limited to the south west of the country, including Cornwall and South Wales, and is only rarely found on our native oaks, despite its worrying name.

The disease was first identified in America, where attacks on American oaks (above right) gave rise to its name, although it does also attack other species of tree and shrubs. In Britain the source of the disease is closely linked to the presence of Rhododendron. This relationship should help limit the impact of the disease to those sites suitable for the growing of Rhododendron, which prefer acid soils.

Apart from Rhododendron the other main host of the disease has been found to be Viburnum. In susceptible trees the disease causes stem bleeding, and it is this that has caused concern in parts of the country where ’Sudden Oak Death’ has not been diagnosed and is unlikely to occur. Laboratory tests have proved that our native tree species are currently resistant to the disease, except where there is a high incidence of Rhododendron, and as such the planting of both English oak - Quercus robur, and Sessile oak - Quercus petrea, is unlikely to be affected.

Cases of stem bleeding in oaks in non-Rhododenron areas are most likely to be suffering from symptoms of Oak Decline, for details see below.

There are two stains of Phytophthora that are the cause of ‘Sudden Oak Death’ in the UK. These are P ramorum and P. Kernoviae. Away from the south west most instances of the disease have been in garden situations involving Camellia, Hamamelis, Leucothoe, Pieris, Kalmia, Syringa, Lilac, Vaccinium vitis-idaea, Drymis winterii and Magnolia.

DEFRA’s plant health division has the overall responsibility for legislation and policy for plants and plant health and coordinates the UK’s plant health policy. The Forestry Commission has legislative responsibility for trees and wood and further details can be found on the Forestry Commission website.

Legislation places particular emphasis on nurseries supplying plants. At Nichsolons we take particular care to ensure that Rhododendrons are not grown or traded on our premises. We also undertake strict quality control measures.

Oak Decline

There have been several reports of stem bleeding on oak away from areas with a high incidence of Rhododendron. This phenomenon has now been diagnosed as ‘Oak Decline’ and can be result of several agents, though not necessarily the same agent in each incidence of the problem.

Damaging factors can include drought, water logging, Phytophthora, beetle and moth attack. The phenomenon causes deterioration in the foliage, and results in branch death. It can lead to the death of the whole tree and can cause stem bleeding. It is not felt that the planting of oak should be affected by the condition which was first reported in the 1920’s and is being monitored by the Forestry Commission.

At Nicholsons we have found that the condition is most prevalent within populations of very old and veteran oaks particularly in old parklands. The older trees being less able to withstand the causal agents detailed earlier. It has not been identified in woodlands under our management, though the Forestry Commission has identified it in mature woodlands.

Further investigation:
For further information on these diseases, these web pages on the Forestry Commission website may be of interest:

Bleeding Canker of Horse Chestnuts: Forestry Commission
Oak Decline: Forest Research
Sudden Oak Death: Forestry Commission

Here at Nicholsons we will happily try to help you identify and solve any problems you are encountering with your trees. If you would like further advice or information, please don't hesitate to Contact us.