Publications & research

Phytophthora kernoviae

An invasive pathogen causing bleeding cankers on beech tree trunks, necrosis on leaves of rhododendrons, pieris and magnolias, and extensive dieback of bilberry.

Disease overview

The novel species Phytophthora kernoviae was first isolated from beech and rhododendron by scientists from Forest Research and the Food and Environment Research Agency (now Fera Science) in 2003. Its likely origins are in the Southern Hemisphere, because it has been found in New Zealand and Chile.

Our research into this highly aggressive pathogen shows it attacks leaves, buds and shoots of under-storey rhododendron in woodlands, as well as ornamental garden plant species. Woodland trees such as beech can also be at risk of infection if they are growing within a few metres of affected rhododendron because of the number of spores released from infected foliage of this shrub.

This resource provides information from our research about the distribution and spread of this infection. Our guide to symptoms will help you to identify infected rhododendrons so you can take precautionary action to destroy these plants.

Disease details

P. kernoviae is a fungus-like pathogen which affects the aerial parts of the trees and shrubs.
It causes leaf necrosis and/or stem dieback in shrubs and bushes and some tree species.
Its principal host is rhododendron, mainly R. ponticum.
Bilberry (V. myrtillus) is also highly susceptible and suffers extensive dieback.
It attacks the inner bark of European beech (Fagus sylvatica) and very occasionally English or pedunculate oak (Quercus robur) leading to bleeding cankers.
Our research suggests that only trees in close proximity to affected shrub vegetation such as rhododendron are at risk from infection, and that infected trees are not contagious and can even recover from infection.
Several garden ornamentals such as Magnolia, Pieris and Drimys species, can suffer from leaf and shoot blight.

Incidence and distribution

It is found mainly in south-west England sites, where the weather favours it and allows it to be particularly aggressive and virulent
It is occasionally found in other locations, including Wales and Scotland, typically in individual plants or as outbreaks in rhododendron.
It has infected thousands of rhododendrons and heathland bilberry plants in Cornwall.
It spread to a small number of woodland tree species (especially beech) and ornamental plants, usually found in close proximity to infected rhododendron.

Full list of plants and trees reported with P. kernoviae infection

Symptoms

Leaf necrosis and/or shoot dieback in susceptible plants and shrubs
Bleeding cankers in trees caused by necrosis of inner bark tissue
Leaf spot in many Magnolia species

These can also be general symptoms caused by some other plant pathogens, including the more widespread Phytophthora ramorum in rhododendron. Please consult our symptoms and diagnosis page for help and advice on identifying P. kernoviae infections in plants and trees. A fact sheet is also available from FERA.

Our Tree Health Diagnostic and Advisory Service offers laboratory-based infection diagnosis. Phytophthora screening provides an accurate diagnosis to support your management decisions and obligations.

Disease management

There is no cure for P. kernoviae infection. Therefore to prevent or limit the spread of disease, owners and managers should consider removing and destroying all infected plants, following the management procedures advised for P. ramorum.

Our research

Our scientists first isolated, identified and characterised Phytophthora kernoviae as a new species in 2003. Our research, funded by Defra and the Forestry Commission’s Phytophthora Programme, investigated the organism's method of spread, the process of infection, and disease management strategies.

Our work covers or has covered:

effective diagnosis and detection of Phytophthora pathogens;
the distribution and impact of recently introduced Phytophthoras, such as Phytophthora ramorum, P. kernoviae and P. lateralis, to trees in Britain;
susceptibility of forest and woodland tree species to P. ramorum and P. kernoviae;
extent of variation in some of the recently arrived Phytophthora species to identify the possible origins, entry pathways and potential for genetic change;
understanding the infection process and disease development in relation to key variables (e.g. host availability, inoculum production and climate); and
how Phytophthora pathogens spread in natural and seminatural environments.

Our research has led to the following publications:

We are among the leading research institutes looking into Phytophthora organisms and the diseases they cause, including Phytophthora austrocedri on juniper, Phytophthora on alder, Phytophthora lateralis and Phytophthora ramorum, the cause of ramorum disease, sometimes known as sudden larch death when it occurs on larch trees (species in the Larix genus).