oak processionary moth

Oak Processionary Moth (OPM) is a relatively new pest to the UK, with several confirmed outbreaks now identified outside of West London.

Since 2006, OPM infestations have occurred entirely around London and surrounding counties. Although OPM specimens have previously been identified in Leeds and Sheffield, follow-up surveys suggested no viable breeding populations were established.

In June 2019, BALI was first alerted by the Animal and Plant Health Agency (APHA) and the Department for Environment, Food and Rural Affairs (Defra) that further cases of OPM had been identified by the Plant Health Service outside of the Core Zone, affecting counties in the Protected Zones including Warwickshire, Gloucestershire and Hampshire. The incidents involved oak trees imported from the continent, specifically the Netherlands, where OPM is a serious issue. Since then there have been further reported sightings around the UK, including in Cardiff.

In July, the Chief Plant Health Office of the Agriculture and Rural Economy Directorate, a department of Scottish Government, advised that all oak trees that have been imported should be sprayed with Deltamethrin, a more effective insecticide for OPM during the summer.

The APHA also issued similar guidance for nurseries in England and Wales, noting the same chemical, Deltamethrin, known in the trade as Bandu or Decis. One litre will be enough to treat approximately 500 trees and can be applied with a knapsack sprayer. PA1 and PA6 operator certificates would be expected. The entirety of the oak tree needs to be sprayed. The hairs from the caterpillars can cause a risk to humans if skin contact is made or if they are inhaled.

Defra also announced stronger measures on the importation of oak trees including:

  • those from OPM free countries
  • those from designated pest-free areas including Protected Zones (PZ) - an area of the European Union declared free of OPM
  • those that have been grown under complete physical protection for their lifetime

The most recent map released by the Forestry Commission has shown a slow but steady spread throughout the London boroughs. Members working in or around London should familiarise themselves with this distribution and identification guide.

BALI members and industry professionals should report any findings of OPM to Tree Alert. You can visit their website here. For more information on how to identify OPM visit The Forest Research website