If you have ever looked at a horse chestnut tree and noticed that its leaves look brown and mottled, you have likely witnessed the effects of the Horse Chestnut Leaf Miner. Here, you will find all that you need to know about this common pest.
Common Name: Horse Chestnut Leaf Miner.
Scientific Name: Cameraria ohridella.
Affects: Horse Chestnut (Aesculus hippocastanum) and some Acer spp.
Impact: Across the UK.
The Horse Chestnut Leaf Miner (Cameraria ohridella) is a larval pest originating from south-eastern Europe.
The first recorded case of the pest in the UK was in 2002, and since then it has spread rapidly across the country.
What is the Horse Chestnut Leaf Miner and What do They Do?
Horse Chestnut Leaf Miners are the larvae of the moth species, Cameraria ohridella.
Between mid-spring and early summer, female Cameraria ohridella moths lay their eggs onto newly opened leaves. Once hatched, the larvae proceed to mine into the two upper layers of the leaf (known as the two epidermis layers) where they feed on the leaf matter to aid their growth process. This is what causes leaves to become crisp, brown and shrivelled.
Once most of the nutrients have been eaten, the larvae pupate within these layers of leaf litter before finally emerging as adult moths who are then ready to restart the process.
Unfortunately, while small populations cannot kill your trees, Horse Chestnut Leaf Miners instead weaken your tree over a sustained period, making them more vulnerable to other pests and diseases. Higher populations also can completely degrade most of the leaf tissue on a tree, which similarly increases a tree’s vulnerability.
How Did They Come to the UK?
The pest is thought to have made its way into the UK accidentally through undetected and infected imported trees; however, this is not for certain.
It is thought that since the first recording in 2002, leaf miners have gone on to spread further through the transportation of hidden pupae amongst leaf litter, but also through adult moths hitching rides on vehicles.
What Should I Look Out For?
- Symptoms will typically begin to show in the lower canopy before making their way up the entirety of the tree.The 3 main symptoms that indicate Horse Chestnut Leaf Miners are present are:
- Visible ‘tracks’ on leaves – these are left by the larvae as they feed within the leaves.
- Shrivelled, brown and crisp leaves – resulting from the larvae consuming vital leaf matter.
- Early leaf fall – Trees can be left completely defoliated due to early leaf fall before the beginning of autumn
How Can I Control/Eliminate this Pest?
Currently, there is no way of getting ‘rid’ of this pest completely, and Horse Chestnut Leaf Miners are now widespread across the UK. Some natural predators, such as blue tits, great tits and marsh tits, feed on the larvae, although it is estimated that only 2-4% of larvae are lost to predation.
There are some third party “horse chestnut leaf miner traps” available online, which use pheromones to lure adult male moths into an enclosure that they cannot escape from. This reduces the likelihood that females can mate and/or lay their eggs in the tree. However, this method will not remove larvae that are already within the tree and the pheromone inserts need to be replaced regularly.
Generally, prevention is better than cure, and it is advised that as a method of control (if your tree does become affected by the mining larvae), you should compost or remove any infected leaves once they have fallen in the autumn. This will prevent the larvae from hatching into adults and reinfecting the tree in the next spring.
Furthermore, efforts are continuously being made to reduce the risk of any additional pests and diseases coming into the UK.
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