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Phytophthora kernoviae

Beech tree showing necrotic barl lesions...

Phytophthora kernoviae is a fungus-like pathogen that affects the aerial parts of the trees and shrubs that it infects.

The pathogen was initially given the working title Phytophthora Taxon C, but the pathologist who discovered it, Professor Clive Brasier, Emeritus Mycologist at the Forestry Commission’s Forest Research agency, named it Phytophthora kernoviae after Kernow, the Cornish name for Cornwall. It was also referred to as P. kernovii for a while.


It is too early to say what the long-term impact will be, but we know that P. kernoviae is capable of causing the same degree of damage to beech as we have previously found for P. ramorum. However, the impact that it could have will also depend on whether P. kernoviae is widely distributed, or is confined only to the locations found so far.


It was first found in October 2003 when, during the course of surveys for Phytophthora ramorum, Forestry Commission scientists isolated and characterised a Phytophthora that was different from P. ramorum from a large bleeding canker on a mature beech from the south-west of England. At the same time scientists from the Central Science Laboratory (now called Fera Science) isolated an identical new organism from established rhododendrons, also from south-west England. Both were confirmed as being the same organism, now formally named as P. kernoviae. Since then it has also been found mainly in south-west England sites, but occasionally in other locations in England, as well as at a site in Wales and a few others in Scotland. All samples submitted are now routinely analysed for P. ramorum and P. kernoviae.

In 2003 a new, fungus-like pathogen, now formally named Phytophthora kernoviae, was discovered on rhododendron plants and a beech tree (Fagus sylvatica) in the Redruth/Truro area of Cornwall, South West England. Since the initial outbreak was detected, the pathogen has been found in other woodlands in the locality and, in the spring of 2005, in the Penzance area of Cornwall. P. kernoviae was also found in a nursery in Cheshire, although this outbreak has since been eradicated, and it has been found at five locations in South Wales. The Welsh outbreaks have largely been contained at four of the sites, and in the fifth, a private garden, there was one infected plant, which was removed and destroyed. Two outbreaks of have been found in garden sites in Scotland since early 2008. 

The principal host of P. kernoviae is rhododendron, mainly R. ponticum, but vaccinium species could also be highly susceptible. P. kernoviae was confirmed on V. myrtillus (bilberry) on a heathland site in Cornwall  in December 2007. However, unlike P. ramorum, P. kernoviae appears to be much more virulent at some specific locations in Cornwall, and rhododendron plants can be heavily diseased or killed by it.


The scale of the Truro/Redruth outbreak was of such concern to the Forestry Commission and Defra that a Statutory Instrument was brought into force in December 2004 to help us contain the disease, and a control area is scheduled in the Plant Health (Phytophthora kernovii¹ Management Zone) (England) Order 2004. The purpose of the order was to supplement the powers available under general plant health legislation, and enable inspectors to close footpaths for the purpose of carrying out eradicatory action. The order also prohibits the removal of all host plants out of the zone without permission.

Research  has already helped us understand how the organism spreads, and the process of infection, so that  disease-management strategies can be developed. Some of the known infected sites in south-west England are designated as experimental sites so that we can learn more about the impact and management of this pathogen in different environments.

Because we know very little about the organism, as a precautionary measure to prevent or limit its spread, we are taking action to destroy infected plants in the same way that we have for P. ramorum. However, our evidence suggests that trees which become infected do not themselves become a source of infection, and might even recover from disease caused by P. kernoviae, and this is being investigated at the research site in south-west England.

Information about P. kernoviae has been given to the EU Plant Health Committee, and all Member States received notification that there was a new Phytophthora affecting beech and rhododendron. We also supplied descriptions (morphological and molecular profiles) to enable scientists to identify it. Similar information has been made available to scientists world-wide. EU Member States now routinely look for P. kernoviae as part of obligatory surveys for P. ramorum, but so far outside the UK it has only been recorded in Ireland and New Zealand. We will continue to be on the look-out for this new Phytophthora species outside the locations where it has been found already.

Treatment and management

Advice to owners, agents and the industry

Host species

Plants known to be susceptible to P. kernoviae include:

Beech (Fagus sylvatica)
Chilean hazelnut (Gevina avellana)
Tulip tree (Liriodendron tulipifera)
Winters bark (Drimys winterii)
Magnolia spp.
Holm oak (Quercus ilex)
Pieris spp.
Michelia doltsopa
Cherry laurel (Prunus laurocerasus)
Ivy (Hedera helix)
Variegated holly (Ilex aquifolium)
English or pedunculate oak (Quercus robur)


Biosecurity New Zealand (2006) - findings of P. kernoviae infecting custard apple (Annona cherimola) in an orchard, and also in a soil sample collected from the Trounson Kauri Park

Report a sighting

Please check our symptom images before making a report.

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Scotland or Wales - Please use Tree Alert.




Last updated: 16th January 2018