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NEWS RELEASE No: 159323 MAY 2013

Aerial spraying to tackle pest caterpillars in woodland near Pangbourne

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Oak processionary moth (Thaumetopoea processionae) larva

The Forestry Commission is planning aerial spraying of an area of woodland near Pangbourne in West Berkshire during May, and is reassuring residents that it poses no risk to human or animal health.

A helicopter will spray the woodland twice over a seven to 14-day period. This is the time when caterpillars of the oak processionary moth (OPM), which is a risk to tree, animal and human health, are emerging from eggs in oak trees.

The product sprayed will be Bacillus thuringiensis (Bt), a bacterial agent which occurs naturally and widely in soil. Bt is very safe when used by fully qualified operators in compliance with the strict health, safety and environmental protection regulations governing its use. Natural England, the government’s advisor on the natural environment, has given authorisation for the operation.

The main, 10-hectare (25-acre) area to be treated comprises Herridge’s and Broom Copses, part of which is privately owned and part of which is public woodland managed by the Forestry Commission. Another privately owned 1ha (2.5-acre) block of trees nearby will also be treated.

If successful the operation would mark a big step forward in efforts by the Commission and West Berkshire Council to eradicate the pest from the Pangbourne area, where only three nests were found in 2012, down from several dozen the previous year. Stewart Snape, from the Commission’s Plant Health Service, explained:

“We know there could be OPM in the woodland because we found a nest in it last year. Most OPM treatment is done by spraying individual trees from the ground, but it’s much more difficult to find and treat the pest in a woodland environment than in trees in a park or street, with a significant risk that some will be missed.

“The most effective way to treat the woodland is to spray it from a helicopter using an ultra-low-volume spray system to minimise the amount of Bt used. Helicopters can fly lower and slower than fixed-wing aircraft, and therefore target the spray very accurately. In addition, the downdraft from a helicopter’s rotor helps to achieve much better penetration of the foliage than fixed-wing aircraft or ground spraying can achieve.

“We have also agreed to conduct a five-year environmental monitoring programme which includes bird, bat, moth and butterfly surveys.”

Pangbourne residents whose oak trees have been found to be infested with OPM have been working with the Commission, West Berkshire Council and an authorised contractor since 2010 to have their trees sprayed. The aerial spraying of these dense woodland areas will significantly support the eradication project.

OPM is a risk to oak trees’ health because its caterpillars feed on the leaves, and in serious cases they can defoliate whole trees, leaving them vulnerable to other pests and diseases.

It is a human and animal health risk because the caterpillars have thousands of tiny hairs which contain a substance which can cause painful skin rashes. Eye and throat problems have also been reported, and the hairs can be blown on the wind and left in the nests.

OPM is a native of southern Europe which was accidentally introduced to Britain. The small Pangbourne outbreak was discovered in 2010, and the eradication programme led by the Forestry Commission and West Berkshire Council has reduced it to only three nests found in 2012.

  • Local residents with enquiries specifically about the aerial spraying may contact the Forestry Comission Public Enquiry line on 0845 FORESTS (0845 367 3787),;
  • More-general enquiries about OPM in Pangbourne should be directed to Arthur Cullen at West Berkshire Council on 01635 519675 or
  • Reports of sightings of the caterpillars or their distinctive white, silken nests can also be made to Mr Cullen, or by using the Forestry Commission’s on-line Tree Alert reporting form available at
  • Anyone with an itchy or painful skin rash or a sore throat and irritated eyes after being near oak trees in these areas should consult their GP or NHS 111. Health information is available on the Public Health England website at under ‘oak processionary moth’.

Further information, including pictures, is available from .

Notes to Editor:

  1. There are two other OPM outbreaks: one in South London, centred on Bromley and Croydon, and one affecting several boroughs in West and South-West London.
  2. Treatment is carried out by qualified pest control operators using techniques and products licensed by the Chemical Regulations Directorate which, when used correctly, are very safe for human and animal health and safety and the environment.
  3. Sighting reports should include a precise description of the location. An Ordnance Survey grid reference is ideal, otherwise an accurate postal address with the full postcode, and/or a clear description of the tree's exact position, is helpful. Digital photographs may be included to aid identification. OPM is most likely to be seen in or near oak trees.
  4. The Forestry Commission is working with landowners and local authorities to eradicate the smaller Pangbourne and Bromley/Croydon outbreaks. However, it is not thought possible to eradicate the West and South-West London outbreak. The objective there is to slow or prevent its spread, and minimise its population and impact.
  5. The best times to tackle the pest are in the spring, with insecticide after the caterpillars have hatched, and in the summer by removing the white, silken nests in which they pupate into adult moths.
    6. OPM (Thaumetopoea processionea) gets its name from the caterpillars' habit of moving about in nose-to-tail processions. It gets the first part of its scientific name from thaumetopoein, the irritating chemical in the caterpillars’ hairs.
  6. A native of southern Europe, OPM has become established as far north as The Netherlands over the past 20 years, aided by plant movements in trade and, possibly, by climate change. It most likely entered Britain as eggs laid on young oak trees before they were imported from mainland Europe for planting here.
  7. OPM will attack other trees such as hornbeam, hazel, beech, sweet chestnut and birch, but usually only where oaks are severely defoliated so that its preferred food of oak leaves is limited.
  8. This press release was edited on 14 May 2013 to amend the Forestry Commission contact details for enquiries about the spraying operation.


  • Forestry Commission / Forest Research – Charlton Clark, 0131 314 6500;
  • West Berkshire Council – Arthur Cullen, 01635 519675;
  • Public Health England - Cian Daly or Tycie West, 020 7811 7242 / 3.