Moths threaten chestnut tree survival

Visit the Père Lachaise cemetery in Paris and chestnut trees shade you as you wander among graves of luminaries such as Oscar Wilde and Jim Morrison.

When Anne Frank hid from Nazis in Amsterdam, the view of a monumental chestnut tree was one thing that cheered her up.

In Cambridge, England, a 200-year-old chestnut outside King’s College chapel is a beloved icon.

But in all those places — and over much of Europe and here at home — the horse chestnut tree is under threat.

Sometimes they fell themselves, unable to bear the weight of their foliage. At other times, city officials move in and cut them down before they collapse.

In summer, their leaves can become so rusty it feels like October. As autumn approaches, many stand naked while other trees still wear their crowns of green.

The culprits? A moth that produces leaf-eating larvae and a bacterium that makes trunks bleed and die.

“In a sense it is almost like a lethal cocktail,” said Dr Darren Evans of Hull University. “If it is under attack by moths, it is probably going to be more susceptible to this bleeding canker, which will kill it.”

The Office of Public Works is understood to have felled several trees in Phoenix Park as a result of the disease, which has spread across the country.

It has flourished across the Continent. The moth lays eggs in leaves and the larvae start devouring them, causing foliage to turn colour as soon as July.

The rusting robs the tree of vital sunlight for key months and, weakened, some fall prey to other diseases such as fungi.

The moth was joined by a bacterium from the Himalayas that causes chestnut bark to bleed a sticky liquid, sapping the tree and in many cases causing death.

“The worst case scenario is that we lose most of our horse chestnuts,” Evans said.

There is historical precedent for the fear: At the turn of the last century, a fungus caused mass extinction of the American chestnut tree in the eastern US.

Europe’s chestnuts came from the Balkans and were introduced to Western Europe 500 years ago.

“Many local authorities are no longer planting horse chestnut trees. What is the point in planting something that is going to be susceptible to attack?” said Evans.