The gall wasp is a pest that mainly affects yucca palms and deciduous trees. It is a black wasp species one to five millimeters in size. It lays its larvae on the leaves of trees and plants. The larvae give off secretions there, which lead to the formation of so-called galls. These galls use the larvae as a shelter and feed and develop there. There are around 100 different species of gall wasp that appear on different plants. Gall wasp infestation is most commonly observed on yucca palms, blackberries, rose plants, maples and other deciduous trees. In addition to the leaves, the gall wasps can also attack buds, inflorescences, fruits and roots. The wasps occur in up to two generations each year.
Prevention - briefly listed
So that gall wasp infestation does not occur in the first place, you should use the
- You shouldn't buy plants from contaminated areas.
- Find out about the distribution of the gall wasp before introducing plants.
- One should not propagate any plant material whose origin is unclear.
- You shouldn't import or buy plants whose origin is unclear.
The damage to the affected plants
The galls caused by the wasps range in size from a few millimeters to several centimeters, depending on the type of wasp. Up to 100 of the smaller galls can appear on one leaf at the same time. The galls can be spherical, lenticular, hump-like or have irregular outgrowths. Some galls are spongy, others have a very firm consistency. The older galls lignify and damage the foliage. Both the
Recognize the gall wasp infestation
Unfortunately it is not very easy to recognize gall wasp infestation in time. It is a discreet pest that is not yet apparent when bought and planted. The well-hidden larvae only become active at the time of budding, and the galls form on leaves, inflorescences and buds. The galls hinder healthy leaf development and damage the flowers. The plant does not die immediately in the case of gall wasp infestation, but it is weakened and loses its productivity. This leads to the fact that further diseases and pests set in. Gall wasp infestation is notifiable in some federal states and control is mandatory.
The fight against the gall wasp
Since the gall wasp was introduced from Asia, there is still little knowledge of effective control methods in Europe. Both mechanical and chemical processes hardly hinder the further spread of the gall wasp. This is because the larvae are well protected inside the bile. Only a few insecticides get there. Cutting out the affected leaves is very time-consuming. In the early stages of the infestation, however, it can be helpful to cut out local foci and destroy them. Contaminated plant material should be burned or disposed of with household waste. In Japan there have been good experiences with biological control methods. A Chinese parasitic wasp species is used for this. This predator, the gall wasp, is able to contain the population and thus the infestation. This method has already been successfully tested in Italy. However, it is currently hardly known what influence the introduction of the Chinese ichneumon wasp has on the European flora and fauna.
Cut back affected plants in a targeted manner
There is currently a real alternative to pruning back the gall wasp-infested plants. Thorough pruning should be done in spring if possible. All affected shoots are to be removed and destroyed. The damaged parts of the plant can be recognized by the characteristic gall formation. It is important that the cut is made before the wasps hatch, because otherwise you have to reckon with an infestation by a second generation of wasps. With a targeted pruning, smaller foci of infestation can be eliminated, but it is very time-consuming and not very effective for larger areas. The only thing that helps here is the use of beneficial insects that decimate the wasp population.
