Tree pests and diseases

Diseases or pests that affect our trees

In this section

The Oak Processionary Moth

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 south east. The moth has been present in TRDC for several years, and is present on several sites owned and managed by TRDC.

OPM is currently a notifiable pest, meaning that landowners are required to report sightings to the FC. The FC are also currently conducting surveillance of OPM across the region. When detected, the FC will normally issue a plant health notice to the tree owner, which requires them to undertake control of the infestation.

Presently the FC are providing financial support to undertake spraying treatment of trees with OPM. However, this treatment can be detrimental to a wide range of Lepidoptera species, and may not be appropriate for use in ecologically sensitive areas, such as nature reserves.

OPM nests can be mechanically removed from trees, although this is a more costly form of treatment, which is not financially supported by the FC. In addition, ongoing annual visits are normally required to remove nests from infested trees.

The removal, or pruning of infested Oak trees can provide more permanent control, but should be a method of last resort in most cases. In certain situations, such as ecologically sensitive areas with high public use where spraying is not appropriate, tree removal may be the most effective option.

It is anticipated that OPM will become more widespread, due to warmer and dryer summers resulting from Climate Change. In the future it is possible that control of OPM will be managed via a risk-based strategy, with control limited to areas of highest public use.

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