Horse Chestnut trees

There are currently 3 main pathogens affecting Horse Chestnut trees throughout the borough.  

Horse Chestnut Bleeding Canker

This disease will effect major branches and tree stems, exhibiting black tarry exudates (bleeding areas) which may girdle the entire circumference, potentially resulting in failure. The reasons for the increase in number of affected trees are currently under investigation by scientists at Forest Research. The Netherlands, France and Germany are also experiencing a similar upsurge of the disease.

There is no chemical treatment currently available to cure or arrest the development of bleeding canker:

• If the lesions become so extensive that the entire trunk is girdled, the tree will inevitably die and have to be removed and disposed of appropriately.
• If major branches are infected and show dieback they should be removed, because recently-dead branches of horse chestnut may be susceptible to sudden fracture and drop as the wood dries out.

Infected trees may survive for many years as disease progression can be very slow or even cease.

Horse Chestnut Leaf Miner

An insect pest, Cameria ohridella, is a leaf mining moth which attacks the leaves of horse chestnut. This pest arrived in the UK in 2002 from elsewhere in Europe.  Larvae of C. ohridella mine within the leaves of horse chestnut, and the damage caused by large numbers of larvae can be striking. Up to 700 leaf mines have been recorded on a single leaf under favourable conditions. Severely damaged leaves shrivel and turn brown by late summer and fall early, well before normal leaf fall in the autumn.

There is no evidence from Europe that trees have died or shown a progressive decline in health as a direct consequence of attack by C. ohridella.  This disease only affects the leaves of the trees, subsequently reducing their photosynthetic ability during the growing season. Disposing of leaves during the winter may assist in limiting the spread of the disease.   

Guignardia Leaf Blotch

One of the most common diseases is Guignardia leaf blotch (caused by the fungus Guignardia aesculi).  This disease can be mistaken for the Horse Chestnut leaf miner. The disease is recognisable by the reddish or dull brown, irregular blotches that are often concentrated at the tips and margins of infected leaflets. The blotches are often outlined by a conspicuous yellow band.  

This disease only affects the leaves of the trees, subsequently reducing their photosynthetic ability during the growing season. Disposing of leaves during the winter may assist in limiting the spread of the disease.   

With all of the above diseases/pathogens we would recommend that specific advice is obtained from a suitably qualified and experienced Arboriculturalist, a list of whom can be at: www.trees.org.uk.