Vienna targets chestnut leaf miner as heat stresses trees

Heat and drought are putting Vienna’s chestnut trees under growing pressure, with the chestnut leaf miner adding to the strain, ORF reported. Vienna City Gardens is focusing protection on particularly valuable chestnut stands.

Some trees in Vienna are flowering for a second time this autumn. Although the bloom may look attractive, it is a warning sign: the trees use up reserves they need for winter.

Warm conditions also help the chestnut leaf miner develop faster. Under optimal conditions, it can produce up to four generations a year in Vienna. Heat does not reduce the infestation, Vienna City Gardens said.

Drought already forces trees to shed leaves. Combined with heat stress and damage from the leaf miner, this can prompt premature emergency growth in autumn, consuming the trees’ winter reserves. The phenomenon has been observed in some parts of Vienna.

Vienna City Gardens removes fallen leaves because the pest can overwinter as pupae in them. The leaves must be professionally hot-composted, as the pupae can survive ordinary composting. The department also uses sprays containing azadirachtin, an active substance derived from neem seeds, on trees in historically significant plantings.

Pheromone traps are used mainly to monitor the moth’s flight and determine the best time for treatment. Beneficial insects are not currently controlling the pest on a broad scale.

Logistical and financial limits restrict spraying. About 3,600 horse chestnuts are treated each year against the first and second generations of the moth, with priority given to historically significant stands such as the Prater Hauptallee and selected trees.