Defra

Why the concern?

Phytophthora kernoviae is a recently-discovered, exotic, fungus-like pathogen which causes damage to trees and shrubs.  It was first found in the south-west of Great Britain in 2003 during official surveillance activities for Phytophthora ramorum causing similar damage to beech trees and rhododendrons.  P. kernoviae is taxonomically a distant cousin of P. ramorum and appears to behave in a similar fashion in GB, sporulating on rhododendrons and causing bleeding stem cankers on susceptible trees. However, there is some evidence that it may be more aggressive on rhododendron under GB conditions than P. ramorum.

It is mainly found in woodlands, parks and managed gardens in the south-west of England and south Wales but has recently also been found on heathland in Cornwall.  It has also been found at one managed garden and one nursery in the north-west of England, as well as two nurseries in the south-west.  In January 2008 it was found for the first time in Scotland at an established garden site. 

Bilberry (Vaccinium myrtillus) is native to heaths, moors and acidic woodlands and forms an integral component of some types of native heathland.  It is commonly found throughout the British Isles and can become locally dominant in some parts of GB.  Vaccinium myrtillus was identified as susceptible to both Phytophthora species in laboratory experiments by the Central Science Laboratory in 2006/07 and was subsequently ound infected with P. kernoviae in woodland in Cornwall in December 2007 and in open heathland in February 2008.  The UK has 20% of the world’s lowland heath and approximately 75% of the total resource of upland heath.  The Government has a Public Service Agreement target for 95% of the area of Sites of Special Scientific Interest (SSSI) in England to be in ‘good condition’ by 2010.  Much of the heathland resource is notified as SSSI and these habitats form a significant proportion of the total SSSI area.  Whilst the potential for the spread of P. kernoviae on open heathland is not known, if significant areas become infected or need to be destroyed as part of control measures there is a risk that this could impact on the achievement of the target.   Further work is currently underway to assess risks to heathland species and identify appropriate control measures in heathland environments.

The only other country where P. kernoviae has been reported is New Zealand.  Reports from New Zealand suggest that P. kernoviae has been present there since the 1950s. 

Following its discovery here, the renamed Phytophthora Programme Board took on responsibility for co-ordinating action and commissioning research against P. kernoviae.

 What is being done?

P. kernoviae was found to be sufficiently widespread in one area of Cornwall, south east of Redruth, that statutory measures were put in place at the end of 2004 (The Plant Health (Phytophthora kenovii Management Zone) England Order 2004) to prohibit the removal of host plants, or parts of host plants (such as cut foliage for decoration) from a designated area without an inspection and written authorisation.  The Order also provides powers to close public footpaths to enable eradication measures to be undertaken.

Unlike P. ramorum there are no specific EU measures, but like any Member State with a new disease problem, we have to report to the European Commission and the other Member States the measures which we are taking to prevent its spread and protect other Member States.  The European Commission may, if it deems it necessary for the purpose of protecting the rest of the Community, seek to introduce regulatory provisions by proposing measures to the Standing Committee on Plant Health.  At the present time there is no indication that any such proposals are planned.

A comprehensive programme of research has been in place since 2003 to support the current eradication and containment action and to help better assess the risk from this pathogen.

What measures are being taken?

Whenever P. kernoviae is found in the GB it is currently subject to emergency phytosanitary measures similar to those taken against P. ramorum, aimed at containment and eradication.   A survey of all premises which trade in plants susceptible to either P. kernoviae or P. ramorum is undertaken annually.   Wholesale nurseries have been subject to a minimum of two visits per year.  An initial comprehensive survey of parks, gardens and woodlands has been followed by an annual targeted survey of approximately 900 sites.  For any site, whether trade, park, garden, woodland or heathland, where infection has been identified, additional visits and appropriate measures have been undertaken to contain and eradicate the disease.

There is no fungicidal treatment which will reliably kill established infections on plants.  Some treatments may help to protect plants from infection, or reduce symptoms.  This may be helpful in slowing disease development and spread, but may also mask infection, making it more difficult to determine whether a nursery is, in fact, pathogen-free.  It is for this reason that there is currently a ban on applying fungicides to plants which are under official hold in nurseries where infection has been found.

The main means of control, both on nurseries and in gardens and woodland sites, has been destruction of infected plants.

On nurseries, susceptible plants within 2m are destroyed and susceptible plants of the same lot or within 10m of the finding are held for 3 months of active growth and inspected at least twice before release. 

At a selected number of woodland gardens and areas of semi-managed or unmanaged woodland, clearance of all R. ponticum, whether infected or not, has proved effective at reducing inoculum levels and appears to have prevented further infection of trees on those sites.  So far almost all of the trees which have been found to have bleeding cankers in GB have either been in direct contact with heavily infected R. ponticum or, within a few metres of it.

Further woodland and heathland surveys are underway to establish the extent of infection.  Research linked to the additional survey work and action is being considered to help inform our understanding of risks to heathland and to inform potential disease management approaches.