Tree pests and diseases

The Oak Processionary Moth (OPM)

OPM is a moth species specific to Oak trees (Querus sp.) thought to have been imported into Britain via infected trees from mainland Europe where it is native. Whilst in some years large infestation can substantially defoliate trees, the moth is primarily an issue for human health.

Fine hairs produced by the moth caterpillars as a defence mechanism for their nests can be a serious irritant to human skin and respiratory system, although it is unlikely to result in serious illness in most cases. Animals, in particular people’s pets, may also suffer from contact with the hairs.

The first reported cases of OPM were in London and the southeast. The moth has been present in TRDC for several years and is present on several sites owned and managed by TRDC. It is anticipated that OPM will become more widespread, due to warmer and dryer summers resulting from Climate Change.

OPM is currently a notifiable pest, meaning that landowners are required to report sightings to the FC. To manage the issue of OPM, the Forestry Commission has divided England into three zones, dependant on the presence of the pest.

Three Rivers District is currently in the established zone. In this zone, landowners are responsible for inspecting and risk assessing for OPM, and making decisions on when to remove OPM from a tree. Government guidance on this can be found here: https://www.gov.uk/guidance/oak-processionary-moth-plan-and-manage-risks.

If you find OPM nests in trees owned by Three Rivers District Council

If you discover OPM caterpillars or nests on Oak trees owned by the council, please report it at: enquiries@threerivers.gov.uk or on: 01923 776611.

Trees and Woodlands Officers will arrange to inspect the trees. If the infestation is found to be OPM, officers will consider the level of risk and whether the nests or caterpillars need to be removed.

Currently, where OPM is found on council trees, which is within three metres of ground level; and / or is present on limbs which directly overhang outdoor, high use areas (such as gardens, and play areas) the council will remove and destroy the nests. In other locations, it will consider the level of risk and may remove nests if the circumstances require it.

If you find OPM nests in your own oak trees

If you discover OPM caterpillars or nests in oak trees growing on your land, it is your responsibility to pay to have the nests removed by a professional. The Forestry Commission can advise on professional firms that provide nest removal services. Do not attempt to remove the nests yourself.

Please report any sightings of OPM caterpillars or nests on public or private land to the Forestry Commission by calling 0300 067 4442 or emailing opm@forestrycommission.gov.uk.