Update on the situation of Cryphonectria parasitica in the United Kingdom
The NPPO of the United Kingdom recently informed the EPPO Secretariat of the detection of Cryphonectria parasitica (EPPO A2 List) in new areas in 2016 and 2017. All previous outbreaks (see EPPO RS 2012/048, 2013/214) had limited distributions and were eradicated or are currently under eradication.
Outer London
In June 2017, C. parasitica was found in Lesnes Abbey (outer London) during an official survey targeting another pathogen, Phytophthora ramorum, which was also present on the inspected site. The site of Lesnes Abbey is a local nature reserve and historic woodland (70 ha) comprised of approximately 75% Castanea sativa (sweet chestnut). The identity of the fungus was confirmed by laboratory analysis (morphology, PCR) of one collected sample. A survey within a radius of 5 km around the site of the initial outbreak, as recommended by the UK contingency plan, led to 4 other findings (all within 10 km of the first finding): 1 in planted street trees (heavily infected), and 3 in parkland trees. Evidence suggest that C. parasitica has been present in this area for at least 5 years. Delimiting surveys, including aerial surveillance are ongoing within 5 km of each site to determine the extent of the disease. It is considered that poor equipment hygiene during maintenance work and the fact that trees were stressed by the presence of other pathogens such as P. ramorum, have probably contributed to the spread of C. parasitica in the affected area.
Southwestern England (Devon and Dorset)
In total, there have been 6 findings of C. parasitica in South-western England: 5 in Devon and 1 in Dorset. In December 2016, C. parasitica was detected on a single sweet chestnut tree on the edge of an office car park in Devon. A 5 km survey around the site of the outbreak led to a second finding of the fungus in a mixed broadleaf woodland, with over 140 symptomatic trees identified. The most heavily affected sweet chestnut trees were those planted in 1995 and 2002, which were traced back to a single UK nursery. While records are no longer available, the nursery has indicated that at that time and until 2013, its chestnut trees had been provided by a sole distributor in the Netherlands. Then, tracing forward studies of trees supplied by the UK nursery in 1995 and 2002 identified 4 other sites (3 in Devon and 1 in Dorset) with trees infected with C. parasitica. Surveillance within 5 km has been completed for 5 of the 6 findings and no further symptoms of C. parasitica have been found. Phytosanitary measures are being implemented at all sites to contain and eradicate C. parasitica.
The pest status of Cryphonectria parasitica in the United Kingdom is officially declared as: Present, only in some parts of the Member State concerned, under eradication.
Sources
NPPO of the United Kingdom (2017-03, 2017-07).