Tree pests
Small insect, big hunger: leaf miner damages chestnuts
Leaves of a chestnut tree in Berlin-Schöneberg, damaged by the leaf miner. Photo
© Christoph Soeder/dpa
Autumn is still far away – and yet many chestnut trees are already shedding brown leaves. A small larva is to blame.
The first piles of leaves are already lying under many chestnut trees. This is not due to dry, hot days, but to a Insect that has been causing problems for trees for years. This year, the infestation with leaf miners is extremely noticeable, says Olaf Zimmermann, entomologist at the Augustenberg Agricultural Technology Center in Karlsruhe. Nationwide, white-flowered horse chestnut trees in avenues, parks and gardens hardly have any leaves left in the summer, and the ones that remain are dried out and wilted. A typical change in color and the first leaves falling off in the second half of August is a typical occurrence, says Roland Mühlethaler from the Nature Conservation Association (Nabu). In general, natural events are shifting forward as a result of global warming, so they are starting earlier and earlier in the year.
Drought exacerbates the problems
According to Mühlethaler, the horse chestnut is particularly affected by drought, in addition to the chestnut leaf miner. “Trees stressed by drought are generally more susceptible to pests,” explains the NABU expert. In northeastern Germany, this is particularly pronounced after several consecutive years of severe drought. “The trees are recovering only slowly, and many have even died.”
Although the horse chestnut is originally a Mediterranean tree, it needs enough moisture. “Years that are too dry combined with severe pest infestation can lead to death in the long term,” says Mühlethaler.
Not a native species
The disappearance of such a non-native species is not a great loss for the native nature. Planting native trees is preferable, not just because of the leaf miner, but in general.
Horse chestnut leaf miners (Cameraria ohridella) are around five millimeters long, orange and white striped small butterflies that lay their eggs on the upper sides of the leaves of the chestnut tree. After about three weeks, larvae hatch and, according to Nabu, eat their way through the inside of the leaf in the weeks that follow. This causes the tree’s leaves to wilt very quickly.
When the leaves die, the trees are prevented from photosynthesizing, which provides energy. In the long run, this weakens them and makes them more susceptible to other stresses. In mild winters, a particularly large number of the moth’s larvae survive.
Help easily available
There is a simple way to help the chestnut tree in front of your house: carefully collect and dispose of the leaves. This removes the larvae in the leaves, from which new moths would otherwise hatch.
Only white-flowering horse chestnuts (Aesculus hippocastanum) are attacked; red-flowering ones of the species Aesculus carnea are not affected.
According to the Nabu, the horse chestnut has been cultivated in parks, gardens and streets throughout Europe since the 17th century due to its attractive foliage and flowers. Since 1989, the leaf miner has invaded almost all of Europe, probably starting from once inaccessible gorges in the Balkans.