Nursery stock growers should be vigilant after confirmed finding of oriental chestnut gall wasp in sweet chestnut trees in a woodland in Kent, and subsequently at a second site in a small number of trees in a single street in Hertfordshire.
This wasp only affects the Castanea tree family, of which, the only species grown in significant numbers in Britain is the European sweet chestnut (Castanea sativa). In several regions of the world, the gall wasp is a threat to sweet chestnutsas it reduces nut production and can weaken the tree, leaving it vulnerable to other diseases. However, the pest does not pose any risk to the more common horse chestnut tree or people, pets and farm livestock.
The Forestry Commission is undertaking a full survey and analysis to determine the scale of the current outbreak and the potential cause of the outbreak. We do not yet know how it entered Britain. However, 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. In addition, the new Observatree group of trained volunteers have agreed to help survey more widely for evidence of the pest.
The UK has Protected Zone Status against this pest, and as such, there is a statutory notification scheme is in place. This means that the UK plant health authorities are pre-notified of pending landings of sweet chestnut plants and planting material so that a proportion can be inspected, allowing inspectors to look for cases of pest introductions such as sweet chestnut blight, and Oriental chestnut gall wasp.
It is a quarantine pest, giving national plant health authorities powers to take measures to contain or eradicate it. During localised outbreaks, control conventionally involves harvesting affected trees by felling or coppicing them and burning, burning, deeply burying, or mulching the lop and top (branch and tree-top material). Mulching (grinding the material into small fragments to destroy the pest) is being used at Farningham Woods. The timber from the trunks can then be used in a bio-secure manner, e.g. for fencing. There are also insecticide treatment options, but these unlikely to be effective for widespread outbreaks in the wider environment because the galls encase the larvae, protecting them from chemical treatments.
Further details on the oriental chestnut gall wasp can be found on the Forestry Commission’s website at http://www.forestry.gov.uk/gallwasp
There is also a symptoms guide which can be downloaded here:
- Symptom Guide (ePub, iBooks compatible)
- Symptom Guide (Mobi, Kindle compatible)
- Symptom Guide(PDF download)
Credits for photographs:
Photo 1 - Oriental Chestnut Gall Wasp - Gyorgy Csoka / Hungary Forest Research Institute / Bugwood.org
Photo 2 - Sweet Chestnut gall from Oriental Chestnut Gall Wasp - Forestry Comission/Fera Science
Photo 3 - Oriental Chestnut Gall Wasp rose-coloured gall on a sweet chestnut stalk -
Crown Copyright/Forestry Commission