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Oak Processionary Moth (OPM) outbreaks

Oak Processionary Moth

The first outbreak of OPM was discovered in Elmbridge and Spelthorne districts of Surrey in 2006. It then spread to Pangbourne in West Berkshire in 2010 and Bromley and Croydon Boroughs in 2012.

As shown on the 2017 map (courtesy of the Forestry Commission), the heaviest reported infestations were in West & SW London.

As of 2108 the infestation has spread rapidly out into the home counties, with many infestations being unreported. Each red dot denotes one tree.

The Forestry Commissions’ 2017 OPM Operational Plan Report states that:

  • 350 sites, 17,687 trees have been sprayed in the control zone
  • 2,111 nests have been removed from 84 sites

 

The threat...

As well as a threat to the trees, the caterpillars pose a health hazard to both humans and animals.  Threat from OPM

... to trees

Once the eggs have hatched and the caterpillars emerge, they feed on the oak trees leaves, slowly defoliating it. This results in a decrease to the photosynthesis process rendering the tree being left in a weakened state and vulnerable to other pests and diseases.

... to humans and animals

The fine hairs from the caterpillars contain a substance that causes irritation and rashes to people or animals. In severe cases, if inhaled, they can also cause breathing problems.

The hairs are easily shed from the caterpillars and can readily can be blown around on air currents, in addition, the nests themselves are often full of hairs.

Please do not attempt to touch the caterpillars or nests.

 

What to look for

Eggs are laid along twigs and branches any time between July to September. The egg plaque may only be 2cm long, which means it’s difficult to spot. Oak Processionary moth nest

When the larvae hatch, they are then visible from April to June, they are brown and approximately 2cm in length. Again, the size and colour make them difficult to see.

As they larvae grow they change into the distinctive hairy caterpillars, moving head to toe, in a procession, which is how they gained their name.

The caterpillars construct silken webbed nests. Theses nests are generally seen on the underside of branches or on the trees main stem, very rarely amongst the leaves. They can be as small as a few centimetres across or stretch for several meters.

The caterpillars then enter the pupae stage after which the moths emerge from the nests mid-July to early September. They only live for 3 or 4 days, but long enough to lay more eggs and begin the life cycle again.

 

Treating OPM

The treatment and removal will depend on where OPM is in the lifecycle.

During April and May, the larvae can be sprayed to control them. Connick Tree Care utilise a fogging machine to apply either a biological or growth regulating agent during the larval stage.

Between June to August is the time when we manually remove the nests from trees.

Nest removal should only ever be carried out by professional contractors, who are correctly equipped and trained to undertake the task.

Nest removal is undertaken by our arborists wearing protective suits and respirators. They ascend into the infested tree and climb throughout the branch structure to the individual nest sites. The nest is then removed and sealed inside a double bag, then removed offsite for incineration at a licensed waste plant.

We do not endorse the use of pyrethroid based insecticides due to their harmful effects to bees and other insects. 

 

Professional Management of OPM

Timing is key to the effective control and eradication of OPM, to ensure that the correct treatment is applied to coincide with the OPM life cycle.

During the course of our site visits, we have noted a marked increase in the spread of OPM throughout our operational area.

If you suspect that you have OPM present in Oak trees on your property, then please contact us for professional advice on how best to control this pest.

 

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Connick Tree Care is certified to treat and manage OPM.

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