The Oak Processionary Moth (Thaumetopoea Processionea) or OPM for short is a dangerous tree pest. The caterpillars feed on the leaves of several species of Oak trees; Turkey, Common and other deciduous oaks. Large processions are capable of ruthlessly stripping whole Oak trees. Therefore, leaving the trees vulnerable to additional pests and diseases not to mention the elements. OPM cannot be ignored. It is an epidemic which is ripping through the South-East of England.
Sometimes OPM will build nests in other trees but they won’t feed there. They only feed on the leaves of Oak trees.
The best time to identify OPM is in the early stages is to find the unbuilt nests. The building of nests generally starts from June onwards. Prior to that, the caterpillars will start to “process” like a marching army around the tree in larger numbers looking for a suitable site. Do not touch the larvae or caterpillars or disturb any nests. They are extremely toxic and dangerous to both humans and animals.
OPM is a major concern for several reasons in the South-East of England. In the later stages of OPM caterpillars development (between the end of May and early June) they are covered in tiny poisonous hairs. If the hairs come into contact with skin it is extremely painful. This includes an extremely itchy rash and sore throat, conjunctivitis and breathing problem. The hairs collect in the OPM nests and are so tiny they can be blown about by the wind. If they land on the floor they are extremely dangerous to animals. If you suspect you have come into either direct or indirect contact with OPM, please contact your GP. If you fear your dog has come into contact with OPM please take them to the vet asap.
Female adult Oak Processionary Moths lays around 300 eggs. All the eggs usually won’t hatch in the same year. Once hatched, the caterpillars pass through six instars [stages]:
- The newly hatched caterpillars are 3mm long, red and have no toxic hairs. (April-May)
- The caterpillars have turned black but still lack hairs. (Early-mid May)
- The caterpillars ‘process’ down from the tree and begin developing irritating hairs. (Mid-late May)
- They start to form silken nests, incorporating hairs and frass. They develop orange dots on their backs. (Early June)
- Trails are visible from the nest back up to canopy where they go to feed. (June-early July)
- The caterpillars have reached adult size. (Mid June-July)
From mid June to September the moths pupate in the nests. The adult moth emerges and lives for 4-5 days.
To prevent any further spread of Oak Processionary Moth (OPM) action is required. What action depends on which zone of the three OPM management zones you are in. Guidance on the zones and further information can be found in the Forest Research The Oak Tree Owners’ OPM manual.
In 2019 we saw a dramatically increased demand for our services to remove OPM. Mole Valley, Surrey Heath, Guildford, Epsom & Ewell, Spelthorne, Woking and Runnymede are all in the control or buffer zone (however almost all of these boroughs have now had cases of OPM). Elmbridge, Kingston upon Thames and Richmond upon Thames, Merton,Brent, Wandsworth, Hounslow, Kensington and Chelsea, Ealing and Westminster are in the core zone.
Surrey Forestry use an environmentally friendly Forestry Commission endorsed chemical called Dipel DF to treat OPM. Dipel DF is a living bacteria [Bacillus Thuringienis] which is consumed by the caterpillars and is not harmful to humans or other animals or wildlife. We apply Dipel DF between mid April – June when it is most efficient and the caterpillars are at their most hungry. Later in the season we use an industrial vacuum to literally ‘hoover’ the nests up (including the caterpillars) out of the Oak trees. They are then removed and incinerated.
It is imperative that you must get the right advise on removing OPM depending on the stage of growth and time of year you arrange action. Spraying will be useless if left too late in which case ‘hoovering’ will be the best course of action.
Surrey Forestry are able to provide a full service to help you to survey and identify, treat and remove OPM. Please do not hesitate to contact us if you fear for any of your Oak trees.