Horse Chestnut Trees Struggle with Disease

Prematurely brown trees fail to produce conkers

Diseases causing premature leaf fall and even fractured branches have affected horse chestnuts trees around London this year.

Infected horse chestnut trees in Twickenham, suffering leaf fall in early autumn

Bushy Park's magnificent avenue of chestnuts are among the many specimens to fall prey to leaf infestation. The horse chestnut trees in Kew Gardens had no conkers this year as a result of disease and pest infestation. On Hampstead Heath, contamination of the water in the Ladies' Pond is being blamed on leaf fall from horse chestnuts infected with leaf disease.

There have been reports of accidents: an Australian visitor was seriously injured by a 10m hybrid horse chestnut, which broke in half and collapsed on her in Abney Park Cemetery, Hackney in October.

According to the Forestry Commission, between 40,000 and 50,000 trees may already be affected - about 10% of all the horse chestnuts in Britain. The LB Richmond has issued a guidance notice describing the three main pathogens affecting horse chestnuts.

1. Bleeding Canker

Horse Chestnut Bleeding Canker is a disease which affects major branches and stems. These exhibit black tarry bleeding areas which may girdle the entire tree and this eventually kill it.

All major diseased branches need to be removed, as diseased branches may suddenly fracture and drop as the wood dries out. There is no chemical treatment currently available.

Infected trees may survive for many years as the progression can be slow and sometimes cease. Scientists are Forest Research are urgently investigating the causes and the Netherlands, France and Germany are also experiencing an upsurge of the disease.

2. Leaf Miner

Horse Chestnut Leaf Miner is an insect pest, Cameria ohridella, which attacks the leaves of the horse chestnut. This arrived in the UK in 2002 from Europe. The larvae mine within the leaves and can cause striking widespread damage. Severely damaged leaves shrivel and turn brown and fall by late summer, well before the normal autumn season. There is no evidence so far that this causes the tree itself to die, as only the leaves are affected: the tree's reduced photosynthetic ability may affect its growth during the growing season.

Experts recommend the leaves should be disposed of during the winter months to limit the spread.

3. Leaf Blotch

Guinardia, or Leaf Blotch, is one of the most common diseases, caused by the fungus Guignardia aesculi. This disease can be mistaken for the leaf miner disease. It is recognisable by the reddish or dull brown irregular blotches that are often concentrated at the tips and margins of the infected leaves. The blotches are often outlined by a conspicuous yellow band. Again this disease only affects the leaves of the trees, reducing their photosynthetic ability and leaves need to be disposed of during the winter to limit its spread.

For more information contact www.trees.org.uk (opens in new window).

HMJ