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OPM manual – 3. Management zones

If you own or manage oak trees in the area affected by oak processionary moth (OPM), you need to check which OPM management zone your trees are in. This will help you to decide what action you need to take.

Three distinct geographical zones have been defined for OPM management purposes (see 'OPM Management Zones' map and lists of areas within each zone below). The official response, and any assistance available to deal with OPM, will depend on which of these zones your trees are in. They are referred to as:

  1. the 'Core Zone' (coloured orange on the map). OPM is established here and control action is not compulsory in this area
  2. the 'Control' or Buffer Zone (an area surrounding the Core Zone, coloured yellow), where control remains the aim to prevent or minimise outward spread into the Pest Free Area
  3. the 'Pest Free Area' (the OPM-free area, coloured green). This is effectively the whole of the remainder of the United Kingdom, where we are required to prevent incursions by OPM or, if they do occur, to take action to eradicate them.


 Map – OPM management zones

Core Zone

The Core Zone is an area where OPM is established and the Forestry Commission does not fund the control treatment in this area. In the Core Zone, it is tree owners' responsibility to check their trees for OPM infestation and to take any necessary action. You will not usually be legally required to do any work to control OPM in this area. This manual provides advice on the action you can take and when.

We strongly recommend that you do take action to protect yourself, your family, neighbours, visitors, staff, pets and livestock and others who have reason to be close to your trees. This will also protect your oak trees from potentially damaging defoliation by the caterpillars. Severe defoliation can leave trees weakened and vulnerable to other pests, diseases and environmental stresses such as drought.

Please refer to the following list and 'OPM Core Zone' map to find out if your trees are in the Core Zone.

If your trees are anywhere in the London Boroughs of:

  • Ealing
  • Hammersmith and Fulham
  • Hounslow
  • Kensington and Chelsea
  • Kingston Upon Thames
  • Richmond Upon Thames
  • the City of Westminster

they are in the Core Zone, where control action is not compulsory, although we strongly advise it.

Map – OPM Core Zone


If your trees are in the local authorities of:

  • Brent
  • Hillingdon
  • Merton
  • Wandsworth
  • the Surrey District of Elmbridge

they could be in the Core Zone or the Control Zone, depending on which part of the local authority they fall in. Please see below maps and descriptions for greater detail:

Control Zone

In general terms, the Forestry Commission will take charge of spray treatment of infested trees in the Control Zone, and there will be no costs for the owner. Treatment involves spraying the trees with an approved bio-pesticide or insecticide. Spray treatment is applied between April and June as this is when the product we use is most effective. 

Nest removal, which is best used as a follow-up supplement to spraying, must be at owners' expense in the Control Zone.

In the event of an OPM find in the Control Zone you may be issued with a Statutory Plant Health Notice (SPHN). The Forestry Commission issues these notices, requiring the owner or manager to take certain steps to control the pest or to outline ways that landowners/managers can work with the Forestry Commission to deliver any control treatment required.

If you are issued with a SPHN, you must follow any instructions provided within the document. If you have any questions about a SPHN you have been issued for OPM, contact the Forestry Commission OPM team.

Note that receipt of a SPHN does not mean that you are in any trouble. Nor does it imply that you have committed an offence, or are at fault for the pest being present on your land. However, failure to comply with the requirements of a SPHN can result in enforcement action.

List of local authorities currently in the OPM Control Zone:

Barking and Dagenham, Barnet, Basildon, Basingstoke and Deane, Bexley, Bracknell Forest, Brent (part of), Brentwood, Bromley, Broxbourne, Camden, Castle Point, Central Bedfordshire, Chelmsford, Chiltern, Crawley, Croydon, Dacorum, Dartford, East Hertfordshire, Elmbridge (part of), Enfield, Epping Forest, Epsom and Ewell, Gravesham, Greenwich, Guildford, Hackney, Haringey, Harlow, Harrow, Hart, Havering, Hertsmere, Hillingdon (part of), Horsham, Islington, Lambeth, Lewisham, Luton, Medway, Merton (part of), Mid Sussex, Mole Valley, Newham, North Hertfordshire, Reading, Redbridge, Reigate and Banstead, Runnymede, Rushmoor, Sevenoaks, Slough, South Bucks, South Oxfordshire, Southwark, Spelthorne, St. Albans, Stevenage, Surrey, Sutton, Tandridge, Three Rivers, Thurrock, Tonbridge and Malling, Tower Hamlets, Uttlesford, Waltham Forest, Wandsworth (part of), Watford, Waverley, Welwyn Hatfield, West Berkshire, Windsor and Maidenhead, Woking, Wokingham and Wycombe.

Pest Free Area

A Pest Free Area (PFA) is an area designated as free of a particular pest. From January 2021 the UK has Pest Free Area status against OPM (see 'OPM Management Zones' map above). Special import and movement requirements apply to prevent infested trees being introduced into the PFA.

The majority of the UK has Pest Free Area status for, and is free from, OPM. This is effectively the whole of the remainder of the United Kingdom, excluding the local authorities listed in the OPM Core and Control Zones, where we are required to prevent incursions by OPM or, if they do occur, to take action to eradicate them. OPM is only known to be present in parts of London and some surrounding areas. The government therefore has a statutory duty to prevent OPM establishing in the PFA.

Outbreaks of OPM in the PFA will be managed by eradication. The Forestry Commission in general will take charge of treating OPM-infested trees in the PFA. Eradication is most likely to be achieved by a combination of methods, which include:

  • surveying trees for evidence of OPM presence
  • correctly-timed applications of insecticide which treat the whole of the tree canopy; and
  • removal and destruction of nests.

Accordingly the Forestry Commission focuses government-funded control effort on the buffer area (the 'Control Zone'). OPM management zones have been defined using the best evidence and scientific advice available to us, and we need to focus public resources on controlling those populations which most threaten to expand into, or further into, the Pest Free Area.

If you do any other work on trees in either zone, especially if it involves cutting branches (tree surgery), there are other considerations which must be taken into account. See section 10 – Other work on oak trees.

The remainder of this manual provides information to help you to help us, the Forestry Commission and the other partners involved, such as local authorities, to prevent or minimise further spread of the pest and to keep its impacts to a minimum.

Next – Biology and life cycle

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