orange-brown colour. Weeping from the bark of
trees can have other causes, such as severe drought or honey fungus attack but, in these cases, the affected area is usually close to ground level. Bleeding canker, by contrast, can be found at points from close to the ground to several metres up the tree.
Both white and red-
flowered horse chestnuts have been affected by the recent upsurge in bleeding canker, and a survey carried out in Hampshire by the Forestry Commission found that the disease affected about half of the trees examined. Whilst mature horse chestnuts can be badly affected, the disease is most damaging to younger trees, as these have smaller trunks and branches which are more easily girdled by the cankers. Girdling of affected branches may take many years on mature specimens, but the trunks of smaller trees may be girdled in just 3- 4 years.
The Cause
Phytophthora can still be found as the cause of some cases of the disease but, in more than ninety per cent of current cases, this organism is not associated with the problem. Instead, tests on the lesions affecting UK trees
have resulted in consistent isolation of a bacterium. In Holland, tests on affected trees have also resulted in the isolation of a bacterium, a known plant pathogen called Pseudomonas syringae. In the UK, the Forestry Commission is attempting to confirm that the bacterium is the causal agent - they will need to inoculate it into healthy material and reproduce the symptoms in order to do this.
Control
Recommendations are at present quite tentative due to the lack of knowledge about the disease. Removal of badly affected trees may help prevent spread of the problem. Lightly affected trees should be monitored closely, but removal is probably unnecessary unless there is a threat to public safety. It is possible that lightly affected trees could recover, although if only a small number of such trees are present in a large area of otherwise healthy horse chestnuts removal may still be prudent. When pruning or felling affected trees, start with those most lightly affected first, and disinfect tools thoroughly. Destroy affected plant parts by burning or burying - do not leave them lying around, and avoid chipping them as this could spread the problem.
It would also be prudent not to replant with horse chestnut in an affected area, and to avoid planting young horse chestnuts in an
area that is currently free from the disease (as there is a potential risk of introducing the disease on planting material).
Guignardia Leaf Blotch
This disease, caused by the fungus Guignardia aesculi, has been around for many years. It is not particularly damaging, as attacks do not usually occur until late summer or autumn, when the tree has completed most of its growth. It could, however, be mistaken for horse chestnut leaf miner. Blotches caused by Guignardia are most often found at the edges of the leaf, and usually have a yellow margin. They are not translucent when held up to light and tiny black spore- producing structures may sometimes be seen if the blotch is examined with a hand lens. If in doubt, and if the tree is in an area where the leaf miner has not been recorded, it would be worth informing the Forestry Commission. For distribution maps of horse chestnut leaf miner, details on sampling, and further information on both this pest and bleeding canker disease, go to
www.forestresearch.gov.uk and follow the horse chestnut link.
Conclusion
Whilst the symptoms produced by the horse chestnut leaf miner can be spectacular, there is currently no information to suggest that this pest will on its own cause serious long-term
Days OFF!
Guignardia Leaf Blotch
damage to horse chestnuts in the UK. However, as well as the adverse affects on the aesthetic quality of the trees, there are some concerns that a reduction in vigour by repeated, heavy infestations may increase a tree’s susceptibility to attack by other pests and diseases such as bleeding canker (particularly if trees are already stressed by environmental factors such as drought). Bleeding canker can certainly cause severe problems, but due to our current limited knowledge about the disease the prognosis at present is uncertain.
If horse chestnuts or other
trees in your care are struggling or showing dieback symptoms it is always best to seek advice from a trained arboriculturalist, particularly where there could be any risk to the public from falling trees or branches.
... or what Pitchcare readers get up to out of office hours
JOHN FARRELL, Technical Director of Baileys of Norfolk Ltd: I’ve always enjoyed sport, both taking part and as a spectator, so working in the sports surfaces industry is a bonus. One of my pastimes, outside of work, could be said to be a bit of a busman’s holiday, I do the match day divoting at Norwich City Football Club ... at the moment the pitch is playing very well, unlike the team! I have twin boys, Lawrence and Milo who have just started secondary school and are now getting into sport. Football boots and kit bags are beginning to clutter the house. Living in the Norfolk we have the wonder resource of the Broads. Over the last couple of years my partner, Mandy, and I have been learning to sail which is great fun. We also have a fantastic dry ski slope in Norwich which we all use. I take it very steady for fear of broken bones, but the kids just fly about as if it were the most natural thing in the world. A few years ago I saw an advert in the local paper for a piano, free to collect. Well, I though it would be a useful for the boys to learn music on. They have no interest in it at all, so I have started to learn how to play; it is a slow and painful process, particularly for the neighbours! Whilst the family is still young I like to spend my free time with them. Generally, it’s doing something mildly active. I’m a strong believer that sport and recreation are great levellers which transcend the boundaries of languages, race, wealth, social standing and disability, so its great to be involved both at work and during my leisure time.
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