The LI’s plant health and biosecurity group wants to draw members’ attention to the pressing need to inspect for Oak Processionary Moth caterpillars and their nests.

OPM Zones, distribution map (last updated 2018)

orange – 2018 core zone; yellow – control/buffer zone; green – protected zone

What do landscape professionals need to do?

OPM is a notifiable pest. It is a health hazard to people and animals in contact with hairs of caterpillar. It weakens oaks through heavy defoliation contributing to long term decline of oaks, OPM increases the tree’s susceptibility to attack from other pests and reduces the tree’s resilience to drought and flood.

  • If you have you been involved in specifying or recently planting oak trees – all oaks except Quercus suber – then you must check these trees as soon as possible before July 2020
  • Identify the caterpillar
  • Report sightings of caterpillars and or nests to Tree Alert online portal

The scale of the problem

The following text appears on page 31 of APHA’s Annual Science and Evidence Review 2019, published on 2 June 2020:

‘The most significant event this year was an unprecedented Oak Processionary Moth (OPM) incident involving all parts of the UK Plant Health Service. This is a UK quarantine pest which causes defoliation of oak trees and hairs on its caterpillars also can cause major health issues to humans and animals. In June, through routine inspection the PHSI detected OPM on recently imported and planted trees from the continent in Southern England. Although this incursion was rapidly and effectively dealt with it quickly became clear that a significant numbers of infected trees had been imported across the UK. Because of the need to quickly trace all imports while their movement information was still fresh and the fact adult moth dispersal would occur from late July there was need to take immediate and decisive action. This led to setting up of an inter-agency UK Plant Health Service (PHS) Incident Management Team (IMT). As part of this APHA took responsibility for tracing investigations (with FC inspecting trees at landscaping locations), inspections at nurseries and on residential property in England and all inspections and action in Wales. This lead to APHA investigating over 2,100 tracing lines stemming from 1,000 consignments and the whole PHS inspecting over 50,000 trees. In total 98 premises in the UK were identified resulting from 156 tracing lines supplied by 28 different Dutch, Belgium [sic] and German suppliers.’

APHA Annual Science and Evidence Review 2019

Increased numbers last year plus hot and dry conditions this spring may well result in a further spread of OPM populations.

OPM is established in London and surrounding areas, but the majority of the rest of the country is a designated Protected Zone (PZ). There are also PZs in mainland Europe. Within the Protected Zone (and in UK) there are restrictions on movements of oak plants to minimise spread of pest.

All imported oak trees into England and Wales now require plant passports, and Animal and Plant Health Agency (APHA) must be notified in advance about all oak (trees, plants and/or seed) imports.

Plant Health and Biosecurity Working Group, 28 May 2020

Remember to be mindful and adhere to current safety guidance if conducting site visits and/or fieldwork during the COVID-19 pandemic. See TGN 02/2020 – Site Visits and Fieldwork During the COVID-19 Pandemic for more information.


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