Horse-Chestnut Leaf Miner
Horse-Chestnut Leaf Miner
Horse-Chestnut Leaf Miner is a tiny moth present throughout England and Scotland. These insects can be extremely damaging to Horse-chestnut trees. Larvae feed within the leaf creating a mine, in which they eventually pupate, developing into a fully-matured adult moth. Leaf mining behaviour provides an abundance of food, as well as offering protection to larvae that are vulnerable to predation. Although the damage caused by these moths may seem unattractive, chestnut trees can survive repeated infestations, with leaves returning the following year. This is because these moths emerge later in the year, and it enables horse-chestnut to become established enough to tolerate attacks.
The larvae of this moth mine the leaves of horse chestnut, damaging leaves and stunting growth.
Although trees can appear unattractive, these moths can't do permanent damage to horse-chestnut.
Adult moths are considered a micro moth, meaning they are very small and hard to identify. They have wingspans of 5mm, with wing scales that are orangey-brown, with white and black banding (like a tiger!). The hindwings comprise whispy, delicate, fringes of hairs. Larvae are tiny, yellow-cream maggots. Pupae, or cocoons, look like small, tan, mealworms. By holding an infested leaf to the light, you can sometimes see pupae and larvae in the mines.
With leaf-mining insects, identification usually is best achieved from the species of the plant infested and characteristics of the mines. Horse chestnuts will flower and grow normally through the spring. The adult leaf-miners emerge come June. You may notice elongate brown blotches spanning the leaves of horse chestnut. It's normal for most leaves to have several mines per leaf. You may see pupae or larvae in the leaves when held to the light. Leaves may drop early, but the tree will recover the following year. Conkers may be smaller in size.
Currently, there is no effective form of biological control in the UK. These trees seem to tolerate the insects fine. You may pick leaves from the ground and destroy any which are infested; this is most likely during July and August. Alternatively, infected leaves collected can be stored in compost. Keep compost sealed the following July to prevent the release of matured moths. Planting red chestnut as opposed to white, can limit attacks by Cameraria ohridella. Pheremone traps can be used to catch active males looking for a mate.
Unfortunately, pesticides are ineffective.