Tree Pests and Diseases


Oak Processionary Moth (OPM) 

The caterpillars (larvae) of oak processionary moth (OPM) are pests of oak trees, and a hazard to human and animal health. OPM was first accidentally introduced to England in 2005, and is subject to a government-led programme of survey and control to minimise its population, spread and impacts.

In 2019 Oak Processionary Moth was found in Three Rivers. The nests were located in Oxhey Woods, Denham Way playing fields and Croxley Common Moor. In July 2019 the nests at these three sites were removed.

In May 2020 the spraying of the trees and surrounding areas took place at Oxhey Woods and Denham Way playing fields. As Croxley Common Moor is a Site of Scientific Special Interest spraying is not allowed to take place. As such Three Rivers, in Partnership with Forestry Commission and Countryside Management Service, will be undertaking visual inspections on whether the moths and their nests return.

Further nests were found in Three Rivers in 2020. This included new nests in Oxhey Woods, Rickmansworth Aquadrome, Croxley Common Moor and Ebury Way. All nests that were found or reported, in these locations were removed and a follow up spraying will be completed in 2021.

If Oak Processionary Moths are found on private land it is the land owners responsibility to have the nests removed, at their expense, by a professional. Forestry Commission will be able to provide assistance to private land owners on who they can contact for nest removal. Do not remove the nests yourself.

The nests are reportable and anyone who thinks they have seen a nest on public or private land can report this directly to Foresty Commission on 0300 067 4442 or

If you would like to find out more about Oak Processionary Moth then you can visit Forestry Commission website here



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