Asian wasp listed as threat to UK's sweet chestnut trees

Forestry commission elevates oriental chestnut gall wasp to high-priority tree pest after 2015 outbreaks

Adam Vaughan

Tuesday 26 April 2016 15.22 BSTLast modified on Thursday 28 April 201612.41 BST

An Asian wasp that threatens the UK’s sweet chestnuts has been designated a high-priority tree pest for the first time.

The oriental chestnut gall wasp (Dryocosmus kuriphilus) was first found in the UK last year, in Farningham woods near Sevenoaks in Kent, and a street in St Albans in Hertfordshire.

On Tuesday the Forestry Commission said it was elevating the wasp to its list of high-priority tree pests because of the 2015 outbreaks.

There are 268 pests on the UK Plant Health Risk register but just 12 are ranked as high priority because of their impact and likelihood, including the fungus that causes ash dieback, sudden oak death disease and the emerald ash borer.

While the wasp poses no risk to humans and pets, its larvae cause abnormal growths — the eponymous galls — on sweet chestnut trees. These can weaken the tree and leave it more vulnerable to other pests and diseases.

The wasp itself emerges in June and July, and has orange legs and a black body, but is easily missed at only 2.5-3mm long.

The galls protect the species from insecticides, so eradication efforts have so far concentrated on felling. Felling trees at the “isolated finding” in St Albans, where it was spotted by the daughter of a tree health volunteer, appears to have wiped the wasp out there.

However, at Farningham woods in Kent, where four hectares of a 79-hectare wood have been felled, further surveys are planned this year.

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