Protecting the Horse Chestnut Trees

The horse chestnut (aesculus hippocaestanum) is a very popular tree here in the city. But unfortunately there is a moth, the so called horse chestnut leaf miner moth, that severely harms the trees in the long term. The chestnut leaves already turn brown and fall off in the summer. The moth larvae spend the winter in the fallen foliage and attack the trees in the following summer again. But this cycle can be interrupted.

More about this moth

The horse chestnut leaf miner moth (cameriaria ohridella), is tiny and only 5mm long. It was first discovered in Macedonia in 1984 and since then has spread all over Europe.

The moth's lifecycle

After the pupae have spent the winter in the fallen leaves, the first moths start hatching out in April. Each female lays up to 40 eggs after mating. The larvae hatch out of the eggs and start feeding on the leaves of the tree, which creates „mines“ inside the leaves. The larvae start to pupate again after just a few weeks and after a further two weeks develop into full grown moths. Three to four generations are possible in each year, because the process from egg to moth is so short. The last generation spends the winter as pupae in the fallen leaves on the ground.

How do the moths harm the chestnut trees?

After the larvae have hatched out of their eggs, the tiny caterpillars feed on the nutritious leaves of the tree for several weeks, destroying many cells which are important for photosynthesis. The tree drops the affected leaves and tries to recover by producing new leaves together with an „emergency bloom“ in late summer. With fewer leaves the tree cannot produce so many nutrients and carbonhydrates and is in a state comparable to malnutrition. The consequences are susceptibility to illnesses, frost damage, slow growth and premature dropping of the chestnut fruit.

By the way: The red chestnut tree (aesculus carnea) is rarely infested by the „horse chestnut leaf miner“ moth, which prefers the white horse chestnut tree.

What can we do to stop the moth?

The most effective and environmentally friendly way is to remove and safely dispose of the fallen leaves, combined with strengthening the natural enemies of the moth such as tits, grasshoppers, ants and parasitic wasps.

Other methods to combat the pest are „tree plasters“ and pheromone traps for the moth males. Injections with insecticide are not an option because of the environmental risk.

How can one help to combat the moth in Freiburg?

It definitely helps to regularly remove the fallen leaves and install nesting boxes for tits in the surrounding areas.