This pathogen is not yet established in North America but appears to pose a significant risk if it is introduced. This previously unknown pathogen was discovered in 2003 during surveys in Great Britain for the sudden oak death pathogen, Phytophthora ramorum. The origin of P. kernoviae is unknown. However, P. kernoviae has been on the Northern Island of New Zealand since at least the 1960s, where it is causing little damage (EPPO Alert 2009).
As of 2009, P. kernoviae remains concentrated in Southwest England, although there are three outbreaks in gardens in Scotland (Denman 2009). Unlike P. ramorum, P. kernoviae is found in only a few nurseries. However, P. kernoviae is proving highly damaging on bilberry (Vaccinium myrtillus) over a wide area of heathland in the Southwest (Denman 09). P. kernoviae was also detected infecting exotic Rhododendron ponticum in a forest location near the south coast of Ireland (Denman 2009).
Heathlands (characterised by dwarf shrubs of the botanical family Ericaceae) are found across northwestern Europe. Heathland is considered an important habitat type in Europe; the U.K and Ireland harbor important components. Four of the seven types of heathland occur in England. Britain and Ireland together support roughly 20% of the world’s lowland heathlands; the UK supports approximately 75% of the total (global) upland heathlands (European Union 2009).
The full host range of P. kernoviae is not known; however, it does include Rhododendron spp. (notably R. ponticum) European beech (Fagus sylvatica), English ivy (Hedera helix), English holly (Ilex aquifolium), tulip tree (Liriodendron tulipifera), magnolias (Magnolia), Michelia doltsopa, fetterbush (Pieris formosa), oaks (Quercus ilex and Quercus robur), and bilberry (Vaccinium myrtillus) (Forestry Commission 2005). Further host studies are under way in the UK. (EPPO alert 09) Tulip tree is native to and widespread in the North American eastern deciduous forests; together with ash it forms the dominant cover in ecologically important cove forests in the central Appalachians. Ash of course is threatened by the emerald ash borer. Other hosts belong to genera with native species in North America: Fagus (beech), Quercus (oak), Rhododendron, Vaccinium and Magnolia.
In spring 2009, the UK Government decided (Walters 2009) to launch a 5-year program aimed at reducing the level of inoculum of both P. ramorum and P. kernoviae to epidemiologically insignificant levels. Program components include removal of the principal sporulating host – the exotic plant Rhododendron ponticum; and the identification and control of any new outbreaks in order to reduce the level of inoculum and minimize the risk of further disease development. There is also continuing research on the two pathogens, the diseases they cause, and more effective control measures. New funding at the level of £4m was allocated for the first 3 years of the program.
Forestry Commission, 2005. Plant Health: Phytophthora kernoviae Frequently Asked Questions. At www.defra.gov.uk/planth/pkfaq.htm. Accessed on December 9, 2005. Link is no longer viable, try https://www.forestry.gov.uk/phytophthora instead.
European Plant Protection Organization. Phytophthora kernoviae Accessed January 2010.
European Union. 2009. Risk Analysis of Phytophthora ramorum, a Newly Recognised Pathogen Threat to Europe and the Cause of Sudden Oak Death in the USA
Walters, K. C. Sansford, and D. Slawson. 2009. Phytophthora ramorum and Phytophthora kernoviae in England and Wales – Public Consultation and New Programme. Fourth Sudden Oak Death Science Symposium June 2009
Webber, J. 2009. Phytophthora ramorum and Phytophthora kernoviae: An Update on Distribution, Policy, and Management in Europe. Fourth Sudden Oak Death Science Symposium June 2009