Plant Oak Processionary Moth (OPM): Update

March represents the start of the period when eggs laid on the branches and stems of oak trees by adult oak processionary moth larvae the previous year, will start to hatch into caterpillars.  This period will last until June/July. The significance of this period for the landscape industry is the risk posed by caterpillars to staff working on and around oak trees, and material removed from oak trees as part of maintenance activities.

Strengthened measures on the importation of most species of oak into England have been put into place to protect native trees from the threat of OPM. The measures permit imports of certain oak trees, if they come from OPM-free countries, from designated pest free areas including Protected Zones (PZ) or have been grown under complete physical protection for their lifetime. 

The aim of measures is to slow the spread of OPM, reduce numbers of the pest and protect oak trees, whilst supporting landowners where OPM is already established. 
 
Despite interceptions throughout England, Wales and Scotland, OPM is currently established in most of Greater London and some surrounding counties.  The measures introduced aim to slow the spread of OPM from these surrounding counties. 
 
In light of the number of interceptions, BALI is urging all members to remain vigilant for signs of oak processionary moth activity regardless of their geographic location.  The precautionary measures are necessary due to the risk posed to native oak trees, humans and some animals whilst the oak processionary moth is in its caterpillar life stage. The risks are twofold:

1. As a caterpillar, oak processionary moths are capable of defoliating large areas of oak trees.  This leaves target trees vulnerable to other, external stresses, such as disease, drought or flooding. 
    
2. The caterpillars have thousands of hairs which, when in contact with human or animal skin, can cause unpleasant rashes.  In isolated cases, the hairs can cause more serious issues such as sore throats, breathing difficulties and eye problems.  The hairs are also commonly found in the nests they live in.

Reporting

All sightings of OPM should be reported to Defra via the Tree Alert system.  See link, below.
https://www.forestresearch.gov.uk/tools-and-resources/tree-alert/

Identification

Photos of oak processionary moth, and the associated caterpillar and nest may be reviewed at the following link: https://www.forestresearch.gov.uk/tools-and-resources/pest-and-disease-resources/oak-processionary-moth-thaumetopoea-processionea/

Further reading:

Oak Processionary Moth map