Oriental chestnut gall wasp confirmed in UK

[Lucan]

Oreintal chestnut gall wasp (Dryocosmus kuriphilus)

 

Just confirmed in Kent. Regarded as the world's worst pest of chestnuts.

[Pinkfoot]

We will just have use pesticides then.

[Adam Bourne]

Oak seem to deal well with gals, and sweet chestnut being oak family I can't see them being much different. I could be wrong

[Steve Bullman]

Doesn't seem a massive issue! copied from Forestry commission site:

 

Oriental chestnut gall wasp (OCGW) was discovered in a woodland in Kent, England, in June 2015, the first time this pest has been confirmed as present in the UK. We are investigating neighbouring woodland to establish the extent of the outbreak, and will take swift and appropriate action. Image courtesy Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org

Description

 

OCGW is an insect of Asian origin which affects sweet chestnut trees in the Castanea family of trees. The only species of the Castanea family grown in significant numbers in Britain is the European sweet chestnut (Castanea sativa).

It does not attack horse chestnut, or ‘conker’ trees, which belong to the Aesculus family, or any other widely grown trees in Britain.

It is a tree pest because its larvae (immature life stage) cause abnormal growths, called galls, to form on sweet chestnut leaves, twigs and petioles (the stalks which attach the leaf blades to the stems). These green or rose-coloured galls inhibit the function of the leaves, weakening the tree and making it more susceptible to other pests and diseases. It can also reduce nut production, and there is some evidence that it can affect timber production.

The wasp does not sting or pose any other risk to human health or to pet animals and livestock, and the affected woodland is not a commercial producer of sweet chestnuts. There are no commercial chestnut orchards in the immediate vicinity.

Identification and symptoms

 

The most obvious indication of OCGW infestation is the presence of the green or rose-coloured galls on leaves. These can grow to 4cm in diameter. No other organism is known to cause galls to form on sweet chestnut trees, so the presence of galls is a reliable indicator of OCGW infestation.

The adult wasp is tiny, being only 2.5 to 3.0mm long, with a black body, translucent wings and orange legs. It emerges in June and July, but its small size means it is unlikely to be noticed by most visitors to affected sites.

Download our symptoms guide onto your mobile phone or tablet:

 

• Symptom Guide (ePub, iBooks compatible)
  
• Symptom Guide (Mobi, Kindle compatible)
  

Or print/save the pdf:

 

• Symptom Guide (PDF)
  

The threat

 

Britain’s suitable climate and the presence of sufficient numbers of its host plant, sweet chestnut, mean that OCGW could get established here. The pest is parthenogenic - it does not need male wasps to reproduce.

Sweet chestnut is valued as a timber species and is locally important in Britain, particularly in Kent, where the small chestnut coppicing industry has been enjoying a revival in recent years. New markets for high-quality chestnut products have been developed.

Sweet chestnut trees are also the source of the edible variety of chestnut, popular in Britain as part of Christmas celebrations. Although there are some orchards, Britain is not a large producer of sweet chestnuts, and most of those consumed in Britain are imported.

Both of these industries could be impacted if the pest were to become established.

The pest also weakens sweet chestnut trees and makes them more vulnerable to other pests and diseases, especially sweet chestnut blight caused by the fungus Cryphonectria parasitica.

Severe attacks can result in tree decline, and loss of or damage to sweet chestnut trees could have an impact on woodland biodiversity.

Outbreak stage

 

Only Farningham Woods, near Swanley in the Sevenoaks District of Kent, England, is currently known to be affected.

Survey and control

 

We have been carrying out annual surveillance for this pest in nurseries, orchards and the wider environment since 2006. This is the only outbreak detected.

We are urgently surveying surrounding woodland within a five-kilometre radius of the affected woodland for any evidence of the pest elsewhere, and assessing what eradication or control action is practicable.

We have served a containment notice on the owners to prevent sweet chestnut material being removed from the woodland.

We will investigate whether there is evidence that the pest might have entered Britain on chestnut plants for planting. If there is, we will trace forward from the source to the destinations of other consignments of plants from the same source to check for other possible outbreaks.

Control options include insecticide treatment. However, insecticide treatment of widespread outbreaks in the wider environment is unlikely to be effective because the galls encase the larvae, protecting them from chemical treatments.

An option in localised outbreaks is to conventionally harvest affected trees by felling or coppicing them and burning, or deeply burying, the lop and top (branch and tree-top material). The timber can then be used in a bio-secure manner, e.g. for fencing.

In the long term there could be the possibility of using a parasitoid organism to achieve a measure of ‘biological control’, but this would need careful research beforehand to ensure that the control organism itself would not cause environmental damage

Action

 

In addition to the actions under Survey and Control (above), we are contacting interested parties and woodland owners to offer advice and guidance. We are circulating a symptoms guide for circulation to woodland owners.

We urge visitors to the woodland not to remove plant material from the woodland. Children should not take galls away to play with. This helps to minimise the risk of accidentally spreading the pest.

Regulation and powers

 

OCGW is a quarantine pest, giving national plant health authorities powers to take measures to contain or eradicate it.

The UK has Protected Zone status for this pest, which means that:

• we have a legal status as being free from Oriental chestnut gall wasp;

 

• sweet chestnut plant imports must be certified as coming from an area declared to be free of the pest; and

 

• we must do annual surveys to check that the UK remains free of the pest.

A statutory notification scheme is in place which means that pending landings of sweet chestnut plants and planting material must be pre-notified to the UK plant health authorities. This helps to raise awareness, build intelligence about the trade, and facilitate targeted inspections. Although this requirement was primarily intended to protect the UK from introductions of sweet chestnut blight, it also helps to provide protection against Oriental chestnut gall wasp.

OCGW is listed on the UK Plant Health Risk Register.

Origin

 

OCGW is a native of parts of Asia which has been accidentally introduced in international trade to Europe and North America. In Europe it has been recorded in France, Spain, Italy, Slovenia, Croatia, the Czech Republic, Germany, Hungary, Portugal and Switzerland.

We do not yet know how it entered Britain, and this is part of our investigation. The main pathways for the pest to travel a long distance are on sweet chestnut plants, or by natural spread, via wind, or in vehicles.

Lifecycle

 

The female wasp lays eggs in the trees’ growth buds during the summer, and the eggs hatch within 30 to 40 days. The early stages of the larvae then lie dormant in the bud over the winter.

Larval activity resumes in the spring, and this activity causes the formation of galls, inside which the larvae develop, in early summer. The galls are formed on young twigs, on leaf petioles or on the midrib of leaves. These green or rose-coloured galls start at approximately 5–20 mm in diameter, and can develop up to 4cm in diameter as the leaf tries to form.

Adult wasps emerge during June and July, leaving exit holes in the galls. The galls turn woody, and can remain on the tree for two years or more.

Reproduction is achieved from unfertilised eggs without mating in a process known as thelytokous parthenogenesis: male wasps have never been recorded.

[Paul Cleaver]

its the veteran trees I would be most concerned about

[Welshwoodsman]

Well get this guys- I know the forester/ coppicer that works Farningham Woods, he and his wife have been friends of my mum's for 20 years+. He has had all his cut timber impounded, and posts/ rails can't leave site, was talking to his wife yesterday- the Plan seems to be going to be clearfell the whole wood. Everything chestnut-there were 50 guys walking around the other day!

 

Contractors meant to be going in with harvesters.

 

Its a SSSI, and my mum was until recently in the management commitee- we gave been walking in the woods there for 40 years.

 

Its just terrible news.

 

Foot & Mouth springs to mind, and another knee jerk reaction.

[timbernut]

A knee jerked in the right direction can be a good thing, although it's very sad that they have to harvest the whole wood (what's its acreage?) think of all the other chestnut woods, including more sssi ones I'm sure, in the south that could be affected, there was no such action taken, apart from saplings being destroyed when ash dieback hit the news, it is now EVERYWHERE in East of England and much further afield, this year it's really taken hold with most coppice regen going back several years is pretty muck dead , not to mention P Ram!

Admittedly there's no guarantee as they don't know it'll work cos they don't know how long the wee beast has been here but surely hitting it hard at the first sign may be a good thing?

[Welshwoodsman]

I agree- IF they can control it, but possibly clearfelling 160 acres if ancient SSSI on the basis it hasnt already spread, seems like a gamble. With all the Spanish salad lorries on the M25, how many other chestnut woods are within easy reach of the motorway? There must be hundreds or even thousands of little copses that could include chestnut.

 

The locals are up in arms, so will be 'interesting' to see what happens. Got to be all down and burnt within 3 weeks apparently.

 

Hopefully they will have a change of tactics- !

[timbernut]

Blimey, that is a good sized area, and you make a good point about the road proximity but do they have them in Spain and are they a real problem (and if not what's the difference gonna be here)? I presume it's mostly coppice, so devastating as it may seem it'll come back

[Paul Cleaver]

Well get this guys- I know the forester/ coppicer that works Farningham Woods, he and his wife have been friends of my mum's for 20 years+. He has had all his cut timber impounded, and posts/ rails can't leave site, was talking to his wife yesterday- the Plan seems to be going to be clearfell the whole wood. Everything chestnut-there were 50 guys walking around the other day!

 

Contractors meant to be going in with harvesters.

 

Its a SSSI, and my mum was until recently in the management commitee- we gave been walking in the woods there for 40 years.

 

Its just terrible news.

 

Foot & Mouth springs to mind, and another knee jerk reaction.

 

sounds terrible - why the SSSI - I hope any drastic measures wont affect the reason for the SSSI what ever that may be