Insects and diseases affecting trees and hedges

Trees and hedges may be affected by a range of diseases and insects. To read more about these, visit the Forestry Commission website.

Oak Processionary Moth in Kingston

The Oak Processionary Moth (Thaumetopoea processionea) is an invasive species which has health implications to trees, humans and animals. Native to central and southern Europe, this pest has been identified in London and is breeding on oak trees in West and South London. It gets its common name from its caterpillars' striking habit of forming long lines, or 'processions', in trees and other substrates. The area affected by Oak Processionary Moth is growing steadily and has been identified within Kingston Upon Thames and neighbouring boroughs.

You must not attempt to handle the larvae caterpillars yourself, or disturb their nests.

The caterpillars have irritating hairs that carry a toxin which can be blown in the wind and cause serious irritation to the skin, eyes and bronchial tubes of humans and animals. They are considered a significant health problem.

The current management process includes removal of any nests up to 4m which ensures they are out of reach of humans and pets. We carry out an annual survey on all RBK oak trees for Oak Processionary Moth. This takes place in the summer and takes the form of a visual inspection from ground level to identify any nests which would pose a health and safety risk - these are currently being removed. The council will generally only remove nests high up within the canopy of the tree if the tree has reached plague levels of infestation and the tree becomes overladen, showing signs of severe defoliation. We do not spray Oak Processionary Moth infested tress with pesticides due to the severe detrimental impact of such practices on populations of other insects, particlarly butterflies and moths. 

The Forestry Commission announced in 2011 that it's no longer possible to eradicate the West and South-West London outbreak and the ongoing objective is to prevent or slow its spread to keep its population as low as possible.

Ash dieback (Chalara fraxinea)

Ash dieback is a serious disease caused by a fungus called Chalara fraxinea. The disease causes leaf loss and crown dieback in Ash trees, and usually leads to tree death.

Young trees cannot recover from infection, but mature trees can survive for a considerable time and some may recover entirely. The impact of Chalara fraxinea depends on tree age, location, weather conditions and co-presence of honey fungus or other pathogenic organisms.