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Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the views of the Arboricultural Association.

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Reminder to report signs of threat to local oak trees

Author:  Forestry Commission
  04/07/2017
Last Updated:  04/07/2017

People in parts of London and the South East are being reminded to look out for and report caterpillars of the Oak Processionary Moth (OPM), which could be damaging oak trees in the area.

OPM is an invasive tree pest and feeds almost exclusively on oak leaves. In large numbers they can strip trees bare and leave them vulnerable to other pests, diseases and drought. The public are being urged to report any sightings to the Forestry Commission, who will safely remove the caterpillars and nests.

The Forestry Commission are working closely with councils and land managers in affected areas to tackle the pest and protect oak trees, through a carefully controlled programme of tree treatment and nest removal.

Alison Field, the Commission’s South East England Director said the public can play an important role in helping to control the pest by reporting sightings, saying;

“We are working hard to protect our oak trees from the devastating effects that large numbers of these caterpillars can cause. To help us to do this, we are asking anyone who spots the caterpillars or their nests to contact the Forestry Commission.”

“However it’s vital that members of the public avoid any contact with the caterpillars or the nests. The treatment of infested oak trees needs to be carried out by specially trained experts and treatment must be carefully timed in order for it to be most effective.”

Infested oak trees should be only be treated by qualified operators under strict controls to ensure it is safe for people, pets, livestock and the environment. Hairs from the caterpillars can cause itching skin rashes and other health problems, so it is important to avoid all contact with the caterpillars and their nests. Anyone who does come into contact with the hairs should seek advice from a pharmacist. If your pet is affected, you should seek assistance from a vet.

The reports that the Forestry Commission have received to date have helped to build a better picture of OPM distribution and has meant that further control measures can be taken.

How to identify OPM

OPM caterpillars;
  • move about in nose-to-tail processions;
  • often form arrow-headed processions, with one leader and subsequent rows containing several caterpillars abreast;
  • are most likely to be found in oak trees;
  • are most likely to be seen in summer;
  • have very long, white hairs which contrast markedly with other, shorter hairs; and
  • do not live on fences, walls and similar structures, as some caterpillar species do.
OPM nests;
  • are usually roughly semi-spherical or teardrop-like in shape before they begin to collapse, when they can become bag-like;
  • occur almost exclusively on oak trees;
  • are almost always attached to the trunks or branches of oak trees; and
  • are almost never woven among the leaves. Silken webbing nests among oak leaves, or in other trees and shrubs and on other structures, are almost certainly NOT made by OPM and need NOT be reported.

If you spot any caterpillars or nests affecting oak trees in your area you can submit a Tree Alert here. Alternatively contact the Forestry Commission on opm@forestry.gsi.gov.uk or call 0300 067 4442.