Oak processionary moth: Plan and manage risks
How to plan for and manage the risks associated with oak processionary moth (OPM) on oak trees on your land.
Applies to England
This guidance is for landowners and site managers who have oak trees on their land, and for people who work on oak trees.
If you’re a private resident with oak trees in your garden, read Managing oak processionary moth (OPM) in England.
Managing the risks from OPM
OPM is regulated as a quarantine pest known to be present in GB. As a quarantine pest, it is under official control measures and cannot be introduced, moved, multiplied or released without prior authorisation. If you suspect you have found an OPM nest or caterpillars, you must report it to us immediately via TreeAlert.
Forestry Commission leads an annual programme of work to manage OPM. The actions required under this approach will vary depending on the management zone in which your site is located.
The current Great Britain OPM management zones map 2024 with exclusion zone is available to view and was updated for the start of the OPM 2023 season. A list of local authorities and wards (ODT, 62.6 KB) that will fall into the buffer zone and established area is also available.
In the established area
In the established area you must report OPM via Tree Alert and should take a risk-based approach to managing OPM. In this area landowners are responsible for the management of OPM on their land, and it is recommended you develop a management plan, which will involve assessing the risks OPM poses on your site. The OPM resource hub contains several tools to understand and evaluate the risks associated with OPM and to determine the appropriate risk management actions.
In the buffer zone
In the buffer zone you must report OPM via Tree Alert. You will then be issued with a Statutory Plant Health Notice (SPHN). You must follow the instructions within the SPHN which may require you to take action. In most cases support is available for treatment of trees within this zone. The SPHN document will explain what action is needed.
In the area free from the pest
This area is officially designated free from OPM and covers most of the country. In this area, the government funds an extensive programme of surveillance to monitor for OPM. Any outbreaks of OPM found in the wider environment within this area are managed by the government with the objective of eradicating the outbreaks. In the area free from the pest, you must report OPM via Tree Alert and you will then be issued with an SPHN. You must follow the instructions within the SPHN which will require you to take action.
Survey for OPM
If you manage oak trees, you should survey your trees for signs of OPM. Read guidance on how to identify OPM in Managing oak processionary moth in England to understand what you’re looking for.
You can also use pheromone traps to survey for the presence of OPM males. Using traps can be an effective tool for identifying new areas where OPM might be spreading. This may be useful in the area outside the established area.
How pheromone traps work
Funnel traps contain a synthetic chemical lure which mimics the sexual pheromone emitted by the female to attract a mate for breeding. This lures the male to the trap. Funnel traps are usually a plastic bucket with the lure under the lid. Male moths attracted to the lure fall through a funnel into the body of the trap.
Adult males are strong flyers and can travel up to 20 kilometres from the nests where they first emerge. Capturing OPM males some distance from known OPM-affected areas does not necessarily mean that OPM has spread to the area of the trap. However, if you catch lots of adult males in a single trap or cluster of traps this may indicate a local breeding population.
Female OPMs are not strong flyers and are rarely found about 500 metres from their original nests.
You should hang the traps as high as possible - at least 10m above ground in the canopy of an oak tree. Any lower will reduce the number of moths caught. You can do this by:
- using a mobile platform (‘cherry picker’)
- climbing the tree
- throwing/catapulting a weighted line over a convenient branch, which you can tie off and use to lower and re-erect the trap when you inspect it
You may need expert help to identify the moths correctly. There are many other species that look similar to OPM. Contact the Forestry Commission for help.
What to do if you find OPM moths
If you trap OPM, you should:
- look for nests in all oak trees within the area of trapping
- inspect again the following year
Any sightings of OPM nests or caterpillars should be reported to the Forestry Commission via Tree Alert. You can also email opm@forestrycommission.gov.uk or phone 0300 067 4442.
Management options to control or manage OPM
In the buffer zone and area free from the pest, the government funds an extensive management programme led by the Forestry Commission. If OPM is found in these areas, it is likely that you will receive a Statutory Plant Health Notice (SPHN). This will include instructions for what you should do.
It is important that landowners, site managers or professional operators report findings of OPM within the buffer zone or area free from the pest to the Forestry Commission to enable government management to take place. If you find OPM nests or caterpillars, report it via the Tree Alert online form.
In most cases the treatment of oak trees that have OPM infestation in these areas will be completed on behalf of the landowner by Forestry Commission. Professional operators should not take action on OPM findings within the buffer zone or area free from the pest without government authorisation, due to the quarantine pest status of OPM.
If you are in the established area and have OPM on your site, there are several management options available to tackle the risks posed by OPM. The measures available to you can be selected depending on the level of risk identified in your management plan and the wider objectives for your site.
Manage OPM: Site zoning, signage, and restricted access
In some cases, direct control action will not be appropriate, and it may be necessary to apply other measures to manage the risks associated with OPM. To manage these risks, you can:
- use signs to warn the public about the presence and risks of OPM
- use site zoning to assess the level of risk in specific areas of the site
- restrict access to high risk areas
These options will not reduce the levels or spread of OPM but will allow you to take targeted action to reduce the public and animal health risks. This is in line with the risk-based approach and is appropriate for all areas, however outside of the established area you will be subject to an SPHN which will specify action needed.
Control OPM: spraying
If OPM is found in the buffer zone or area free from the pest, action must be taken to control OPM. A government led management programme operates in these areas, including in many cases support to treat OPM. It is likely that you will receive a Statutory Plant Health Notice (SPHN), which will include instructions for what actions are needed and what you should do.
Action may also be appropriate in the established area dependent on the approach set out in your management plan. To control the spread of OPM you can:
- spray the affected tree with insecticides
- if you have oak trees within 50m of the affected tree it is recommended you also spray those trees
To spray, use the 2 insecticides licensed for control of the larvae, or caterpillars, of OPM. These are:
- bacillus thuringiensis var kurstaki (BT)
- deltamethrin
The status and availability of chemicals can change from year to year, so it is important to check the manufacturer’s label and the Health & Safety Executive (HSE) website to ensure that there is current approval for the use intended.
Where pesticide is needed, it must be applied by appropriately qualified and equipped professional operators. You can find a professional on the Arboricultural Association website to carry out this work.
Do not spray trees once the moths have flown - this is not effective. Only use insecticides on trees with larvae/caterpillars. Where pesticide use is needed, it must be applied by appropriately qualified and equipped professional operators.
If your trees are on a site of special scientific interest (SSSI), you’ll need permission from Natural England before any work is carried out.
Control OPM: nest removal
If the nests pose a threat to public and animal health, you can remove the nests with their larvae using a vacuum cleaner or by hand.
You should use an expert to do the work. You can find businesses able to carry out this work from:
- the Arboricultural Association
- your local borough or district council’s tree officer
Removing nests and larvae does not completely eradicate OPM but is considered more environmentally friendly and has little impact on other wildlife. It may be the only option if spraying is not allowed, for example if your trees are on a site of special scientific interest (SSSI).
Further information about risk management options and control measures is available on the OPM hub.
Public and animal health risks
If you have OPM on your oak trees, you must protect yourself, the public and animals from health risks. Read the risks to people and animals from OPM on Managing oak processionary moth in England.
If your work brings you into close contact with oak trees, you should take care to protect yourself.
Site users and visitors
If you are encouraging visitors to your site, you may wish to consider actions to mitigate against public health risks such as:
- signs warning people about the presence of OPM and what to do/what not to do
- restricting access to high risk areas
- working with stakeholders, such as friends’ groups, to raise awareness
- newsletters and social media posts
- control actions, such as spraying or nest removal to reduce levels of OPM
Working on oak trees with OPM
Before starting work on trees with OPM, consider the likelihood and risk of exposure to OPM.
When you’re working in areas where OPM is known to be present:
- avoid direct contact with caterpillars and their nests
- wear long-sleeved tops and long trousers with the cuffs tucked in and consider gloves, goggles, and a balaclava to protect your head and hands
- wear a dust mask to stop hairs entering your mouth, throat, and airways
When removing nests, make sure you have the right personal protective equipment (PPE) to protect your eyes, mouth, and skin. This includes:
- face mask - filtering half mask FFP2 or FFP3 (European standard EN149: 2001), disposable, to protect against particles
- goggles - complying with European standard EN166 and either Code 4 or Code 5
- disposable spray suit - an impermeable protective suit suitable for insecticide spraying will also protect against the caterpillars’ hairs
- gloves to prevent skin contact - robust water- and chemical-resistant gloves, as used for spraying operations
- boots to prevent skin contact - water-proof and chemical-resistant rubber boots, as used for spraying operations
All these items are available from safety equipment suppliers.
Employing people exposed to OPM
If you employ people who are exposed to OPM, you have legal responsibility for your and their safety. Before you start work on the oak trees, you must:
- complete risk assessments
- identify and use control measures
- provide people with suitable PPE
- have a system for people to report defective equipment
- provide people with information and training on the health risks and control measures including skin checks
- provide suitable welfare facilities such as washing facilities
- provide a health surveillance programme
If you’re exposed to OPM at work, make sure you:
- take care of your own health at work
- follow recommended systems of work
- use the equipment provided, including the PPE
- keep equipment, such as ropes and gloves, used on OPM-infested trees separate from equipment used on other trees
- report any defects or problems with the equipment
- attend any training or instruction
- tell your employers if you have health concerns
- attend any health surveillance programme or health checks put in place
Speak to a medical professional if you have any concerns about your or anyone else’s health after working near OPM.
Updates to this page
Last updated 26 April 2024 + show all updates
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Updated to reflect the 2024 season and added a link to the new map.
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General page updates
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First published.