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Conkers on horse chestnut trees threatened by moth pest
By Emma Brennand
Earth News reporter

Horse chestnut seed
Could conker championships become a thing of the past?

A common insect called the leaf miner moth does more long-term damage to horse chestnut trees than thought.

Previously the moth was thought to cause only cosmetic damage, but a study published in the journal Urban Forestry & Urban Greening shows the moth larvae attack the tree's leaves, reducing their ability to capture sunlight and turn it into food.

This loss in ability to produce energy, dramatically reduces seed size and quality, potentially stunting the tree's growth.

The horse chestnut tree was first introduced to the UK in the 1600s.

The future does not look promising for a tree that, up until six to eight years ago, had thrived in the UK for the past 400 years
Dr Glynn Percival, University of Reading

Its white flowers are now a common sight in UK towns, cities, parks and woodlands.

However, over the past eight years, this tree has been under attack by the leaf miner moth Cameraria ohridella.

"Infected leaves are covered initially in small, brown patches which spread rapidly across the entire tree," explains Dr Glynn Percival from the University of Reading, UK.

"Eventually leaves die and fall prematurely."

This new study shows that the damage may be long-term, effecting the tree's growth and reproduction.

Light-weight conkers

The researchers report that the average seed weight, germination and growth rates decreases by up to 48% in trees showing infestation.

And conker weights are halved in trees that show a very large amount of leaf damage.

The team also observed decreases in stem growth, and in levels of sugars and starch in roots and twigs.

Horse chestnut leaf miner moth

This reduced the overall tree's growth and ability to store energy.

The largest impact was during the growing season, between late June and early July.

This is when the tree switches from vegetative growth to storage and reproduction.

"It is debatable whether smaller trees would be capable of long-term survival," Dr Glynn writes in the journal article.

"The future does not look promising for a tree that, up until six to eight years ago, had thrived in the UK for the past 400 years."

The general consensus amongst researchers remains that the horse chestnut leaf miner is a cosmetic pest.

But Dr Glynn believes that unless this invasive pest can be better controlled, horse chestnut-lined streets might be a thing of the past, as people opt for ornamental trees which are aesthetically pleasing all year round.

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