Irish horse chestnut trees threatened by new parasite

Horse chestnut trees in Ireland are threatened by a new parasite which has killed 50,000 trees in the UK.

Bleeding canker is killing horse chestnuts in significant numbers in Ireland. It is caused by the bacteria Pseudomonas syringae pv aesculi, which is widespread in Europe and is increasingly common in Ireland, said the forest service of the Department of Agriculture.

Bleeding canker, which withers the crowns of horse chestnuts, affects trees of all ages and often kills them.

Bleeding lesions

The forest service said the symptoms are mostly in the form of bleeding lesions on the bark. These produce rusty-red, yellow-brown or an almost black sticky ooze.

The causal agent of the disease is not listed as an EU quarantine pathogen and so no statutory measures are being taken, the forest service said.

In a statement, the department said it co-ordinates efforts with local authorities and the Office of Public Works on treatment and measures to limit the spread of the disease.

It has been noted in the UK for over two decades and the Forestry Commission has tracked its progress from the south of England across the UK and into Ireland. The commission said it appears to have spread faster in the last few years.

The disease has become a threat to Irish trees along with ash dieback, beech wilt, and sudden oak death or decline.

Expert Thomas Pakenham said the four diseases of ash, chestnut, beech and oak represented the “horsemen of the apocalypse” for Irish forestry. He said his estate, Tullynally Castle in Co Westmeath, loses one horse chestnut a year.

He attributed the disease to globalisation, with parasites probably coming on pallets from the Far East. But, he said, Indian and Asian horse chestnuts seem to have become immune, which offers hope.