Tree officers group issues advice on OPM outbreak management

The London Tree Officers Association (LTOA) has issued advice for tree managers faced with new oak processionary moth (OPM) outbreaks, as the noxious tree pest spreads around the country.

Image: Andreas März (CC BY 2.0)
Image: Andreas März (CC BY 2.0)

Currently the Forestry Commission is leading on controlling the moth, whose caterpillars release hairs harmful to humans and animals.

It has separate regimes within the "core" zone of west London where the initial outbreak occurred, and across the rest of the country, termed the "control" or "protected" zone.

With early first-hand experience of OPM, the LTOA has issued guidance to tree managers on its management since 2010.

Outbreaks within the control zone must be notified to the Forestry Commission, which then manages the pest within these areas. "It is also crucial that the problem is communicated to key stakeholders within any organisation, ensuring that the matter of OPM is acknowledged and considered at an appropriate level," the LTOA says.

For a local authority, this will mean at a corporate level, where decisions can then be made to determine the extent of the problem, the risk that needs to be managed, how and by whom, and how it is to be funded.

It points out that within the core zone by contrast, the management of OPM is the responsibility of the tree owner, who needs to consider the risk to human health," the LTOA says. "It is this consideration that will help the tree owner to determine a form of management."

In such cases, a strategic approach should be data-led, allowing tree owners to categorise risk based on the position of vulnerable trees in relation to human activity, so setting surveying requirements to determine if infestations are present.

In such cases, managers need to be aware of the management options available to them, from prophylactic chemical control to manual nest removal, and also of the constraints on these options, for example the limitations on chemical control near waterways, as well as the burden placed on operatives, who have to wear uncomfortable protective equipment during summer weather.

The LTOA adds that the risk OPM poses to workers "has been understated", and says: "Arborists that have been affected by OPM become increasingly sensitive to the effects of the irritating toxin thaumetopoein, so much so that it is no longer acceptable for them to be exposed to the irritating hairs that are produced by the developing caterpillars."

And it warns: "If taken lightly, the risk to our much needed tree professionals could result in companies having an inability to work on oak trees, or at worst, putting hypersensitive operatives at an unacceptable risk of harm."

The LTOA also warns against using blowtorches to destroy nests, which can cause caterpillars to eject their toxic hairs, and it says felling oak trees to avoid the OPM management burden should also be avoided as oak "is of huge significance to our environment and the multitude of species that identify with this cherished tree".

It urges managers to communicate the dangers and approporate response to OPM among the public, such as via timely press releases, online guidance, presentations to community groups and volunteers and signage.

"Within boroughs that have learned to live with OPM, tree owners have effectively communicated the dangers that it poses, and the public have taken personal responsibility for avoiding the pest and reporting it to the tree owner," it says.

London Borough of Richmond arboricutural manager LTOA Executive Committee member Craig Ruddick said: "Communication is a hugely important part of OPM management - not only to senior officers and elected members in local authorities so that funding can be sought, but also ensuring the public are informed so that risks to health are minimised."

So far this season, OPM has been found in over 60 locations beyond the original outbreak area.

London borough of Merton arboricutural manager Dave Lofthouse, also a LTOA Executive Committee member, said: "Where eradication is still possible, local authorities should be making every effort to direct resources towards this."

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