Forestry Commission logo

Oak processionary moth - September 2014 update


The background to OPM can be found on the FC website; in summary, OPM was first found in England in 2006. Since 2013, additional Defra resources have helped fund an enhanced OPM control programme, to complement the collaborative OPM control activity being undertaken by affected landowners and managers. This report provides an update on control and survey activity up to the end of September 2014.

Principles behind 2014 activity

In 2014 the OPM programme was based on some key principles (with a few site-based exceptions):

  • Trees infested in the past and treated but which have not been found to be infested in the last 2 years, were not sprayed again unless new infestation was found. Therefore previously infested trees from 2011 and before, but not found to be infested in the summer of 2012 and 2013, were not sprayed.
  • New trees found to be infested last season were sprayed.
  • Where infested trees were identified for spraying in 2014, all potential host oak trees within 50m were sprayed.
  • The majority of the control programme used Bacillus thuringiensis (Bt) and Dimilin to control OPM as these chemicals have the least impact on non-target species.
  • Where surveys during 2014 identified infestation of oak trees and the window of opportunity for effective spraying is no longer available, manual nest removal was carried out before the moths emerged to reduce the likelihood of OPM spread. This involved issuing the statutory plant health notice and nest removal, either by teams funded by Defra, or by the landowner.
  • The survey looked at host trees within outbreak areas, surveying 2km beyond the known furthest extent in 2013. In West London, FC survey resource was focussed on the outer ring of infestation and 2km buffer while partners were expected to survey the core infestation area. In Pangbourne and Bromley/Croydon, FC survey resource covered the whole outbreak area with a 2km buffer.
  • Pheromone traps to capture male moths were set up 2 km outside the 2 km buffer survey zone i.e. up to 4 km from known OPM infestations.

The appendix maps show the location and extent of survey and pheromone traps.


The following provides the amount of control work that was carried out. The term ‘site’ refers to an area of work where OPM is found. A site could be a one tree in a garden or hundreds of trees, for example, on a golf course. The data includes Defra-funded activity undertaken by the Forestry Commission and activity reported by partners.

Sites sprayed 322
Trees sprayed 46566*
Sprayed sites subsequently found to be reinfested 94
Nests removed 12755

* Number of trees sprayed excludes The Royal Parks and those sprayed by helicopter at Pangbourne


Sites surveyed - summer 2014 2410
Trees surveyed - summer 2014 54804
Sites infested with nests 322
Trees infested with nests 4043
Total nest numbers 12513
Number of surveyors submitting records using the reporting app 63
Number of records submitted to the app (one record could include location of many trees) 5685
Number of pheromone traps deployed 302



Public information posters produced and distributed 2400
Public information leaflets produced and distributed 80000
Addresses to which leaflets and posters were distributed 1863
OPM signs for contractor vehicles (2 per vehicle) 30
Press releases at key milestone points in OPM season 3
Portable twin-set banners produced and provided to all affected local authorities, and to Transport for London 36
NGO on-line forums engaged 2
FC site signage produced and deployed (Sulham Woods) 1
Tweets sent from FC accounts 5



Appendix I shows OPM was found beyond last year’s previous known extent, and preliminary results indicate OPM infestation ~50% greater in area than 2013. In 2013 the area increase was 17%, but in previous years the area of spread averaged 50%. OPM has been found in Surrey, with Elmbridge and Spelthorne Districts affected. Hillingdon, Harrow and Brent are new boroughs with OPM, and in Westminster it has been found at London Zoo in Regent's Park, close to Camden Borough.

The finding of wider infestation is not necessarily an indication of spread this year, but rather as a result of more extensive survey work and detection of old infestations.

East London intervention

After a report of an infested tree adjacent to the Olympic Park in Stratford, a statutory plant health notice was issued and the infested tree destroyed within a week of notification. The tree was planted in 2013 as an 8-10m tall semi-mature tree, and surveys were carried out of all potential hosts trees within a 2km radius. These surveys found no further evidence of OPM infestation.

Pheromone trapping programme

Appendix II shows the extent of the pheromone trapping programme, and that male moths were captured 4km beyond the 2013 known extent. The extensive trapping deployment was a new feature of the OPM programme this year, and used improved trap techniques. It is known that male moths can fly more than 20km, so more work is needed to interpret the pheromone trap results.

Tree Health

Whilst some of the nests found this year were particularly large, and there was some evidence of tree defoliation, no major defoliation was reported.

Human Health

Public Health England has continued to monitor health effects. It is known that there were some reports of health issues arising at a small number of school premises.


For the second year running the visual survey programme has not found any OPM nests. The more extensive pheromone trap programme has detected a single male moth in each of 3 traps in locations further SE from the centre of Pangbourne, as indicated in appendix II.


36 pop-up portable banners and posters were distributed to all affected local authorities and Transport for London to raise awareness of OPM and promote reporting of sightings.

OPM leaflets and posters were provided to Defra-funded control contractors and surveyors, and to a range of premises and organisations. We targeted those organisations and premises whose staff, members, customers and/or visitors were at greatest risk of exposure to OPM, e.g. golf clubs and public parks, or who would benefit from knowing how to recognise OPM contact symptoms and what to do about them, e.g. vets and pharmacists. A small number of GPs’ surgeries requested copies when invited by PHE to do so.

Removable signs were distributed to pest control contractors to erect on the sides of their vehicles while engaged on OPM control operations, to inform passing public.

The FC proactively issued 5 tweets from FC accounts and engaged in on-line forums of two NGOs which were disseminating misleading and incorrect information about aerial treatment at Pangbourne. Rapid responses on the FC website helped counter this misleading information.

An OPM-themed garden was installed at the Chelsea flower show, sponsored by the City of London Corporation. The garden attracted a huge amount of interest, engaging with around 12,000 people to highlight the issue of OPM and what is being done to control it.

Weather conditions

This year’s results will have been affected significantly by the weather conditions, which were very favourable for OPM in comparison with 2013. The 2013/14 winter was very mild and there were no late spring frosts recorded. The spring and summer of 2014 have been largely dry and warm. Natural mortality of OPM appears to be much less than the 2013 season.


The OPM control programme has been implemented as planned, with 322 sites out of 342 sites sprayed. Weather conditions have been very favourable for OPM development, which is likely to have been a key factor for the increased OPM distribution compared with last year. That said, we are confident that the control programme employed has limited the level of infestation and distribution compared with continental situations where OPM is not controlled.

Next Steps

  • Take stock of what this year’s findings mean for the 2015 programme and longer term strategy.
  • Identify targeting and resources for an OPM winter survey that will further inform the 2015 OPM programme.

Appendix I - OPM nests, London, 2014

In the map below, the red and green dots indicate oak trees inspected for OPM presence in 2014. The red dots indicate trees where OPM was found, and the green dots where it was not found.

Map showing oak trees inspected for OPM presence in 2014.

Map of OPM nests, London, 2014 (PDF, 2.7MB)

Appendix II - OPM pheromone traps, London and Pangbourne, 2014

In the map below, the dots indicate pheromone traps set to trap adult male moths in late summer 2014. The red dots indicate traps where moths were caught, and the green dots indicate traps where none were caught.

Note that male moths are known to be capable of flying at least 20km, whereas females lay their eggs mostly within 1km of their nest sites. Therefore presence of male moths in pheromone traps is not necessarily an indication of local infestation. However, by analysing the numbers of males caught in each trap, we are better able to target winter surveying for nests that might have been missed during the summer. 

Map showing pheromone traps set to trap adult male moths in late Summer 2014.

Map of OPM pheromone traps, London and Pangbourne, 2014 (PDF, 3.5MB)