SWEET chestnut (Castanea sativa) was brought to Britain by the Romans for nuts, but instead evolved into a commercial timber tree.
In 2012, sweet chestnut was touted as a natural replacement for native common ash (Fraxinus excelsior), already on the road to ruin from Chalara ash dieback disease (Hymenoscyphus fraxineus).
But sweet chestnut had a brace of its own problems, including one caused by the fungus Cryphonectria parasitica, or chestnut blight, the “world’s worst disease” of Castanea (Mabbett, 2017).
The following is a timeline for chestnut blight from the first UK finding in November 2011 to the last outbreaks, reported by the Forestry Commission (FC) in March 2018:
- November 2011 – the first finding in orchards at a Warwickshire farm on trees sourced from a French nursery and planted in 2007. Of 300 trees planted, 50 per cent were infected.
- November 2011 to April 2013 – a trace forward exercise by the FC and FERA identified 11 more diseased sites, including an orchard in Sussex, a plant nursery and private residences, including one in Herefordshire. The exact location of the outbreaks was never disclosed by these authorities.
- July 2015 – the FC says chestnut blight is eradicated from the UK.
- July 2016 – a new outbreak is found near Maidstone, Kent, on trees planted in 2009.
- December 2016 to May 2017 – six outbreaks recorded in Devon and Dorset. Detailed maps from the FC include ‘movement prohibition zones’ for Castanea and also Quercus (oak). Cryphonectria parasitica infects oaks in Eastern Europe.
- July 2017 – one outbreak in London is reported as East London by the FC and South-East London by DEFRA.
- September 2017 – two outbreaks in Derbyshire and one near Reading, Berkshire.
- March 2018 – two more outbreaks in Devon and one in Derbyshire, the first outbreak recorded in Leicestershire and seven more in London.
The FC provided detailed maps showing movement prohibition zones in Devon and Dorset. It became illegal to move sweet chestnut material including plants, logs, branches, foliage and firewood out of, or inside, zones within a 2 km radius of affected sites. The same restrictions applied to oak within a 1 km radius of the affected sites. In contrast, neither the FC nor DEFRA have divulged even the nearest town in the case of the eight outbreaks in London and those in most other parts of England.
Chestnut blight has been present in the UK since 2007 (at least) but is apparently not spreading from sites where infected trees were planted. The FC says there is no evidence of the disease spreading from outbreak sites into the wider environment, although one site in South-West England showed evidence of localised spread within the affected woodland.
Considering the amount of damage caused by this pathogen in Europe and North America, where four billion North American chestnut trees (Castanea dentata) were killed down the Eastern seaboard, we appear have got off lightly.
REFERENCES:
Adamcikova, K., Kobza, M. and Juhasova, G. (2010), ‘Characteristics of the Cryphonectria parasitica isolated from Quercus in Slovakia’. Forest Pathology 40(5), 443–9.
FERA (2013), Rapid pest risk analysis for Cryphonectria parasitica. 23 pages. 2013. FERA Science Ltd (FERA) National Agri-Food Innovation Campus, Sand Hutton, York, YO41 1LZ.
Mabbett, T.H. (2009), ‘Not the same old chestnut’, Forestry Journal, November 2009, 48–9.
Mabbett, T.H. (2017) ‘Sweet chestnut overtaken by events’, Forestry Journal, February 2017, 33–5.
Morath, S., Fielding N., Tilbury, C. and Jones, B. (2015) ‘Oriental Chestnut Gall Wasp’, Quarterly Journal of Forestry, 109(4), 253–8.
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