A serious disease of bilberry in the Cannock Chase Country Park

Bilberry showing symptoms of Phytophthora

On 2 January 2009 a stand of bilberry (Vaccinium myrtillus) was found in Brocton Coppice with dieback and black diseased patches on the shoots.  Complete death of some plants had occurred.

Samples of the diseased material were analysed by the Food and Environment Research Agency, and a micro-organism identified as Phytophthora pseudosyringae was isolated.  This alga-like fungus causes rotting of roots of deciduous trees in Europe, and is associated with the condition known as oak decline.  It has only rarely been recorded in the United Kingdom, and there appear to be no previous records, anywhere, for infection of bilberry. 

A number of survey teams have been deployed on the Chase since January, carrying out a rapid initial assessment of the extent of infection.  Surveyors from Natural England, the Staffordshire Wildlife Trust, the Voluntary Warden Service, ecological consultancies and students have been working with County Council staff, and we are very grateful for the assistance we have received to date.  The work of the survey teams has been made easier by the use of a field testing kit, called a Lateral Flow Device (LFD).  A sample of the plant material showing symptoms of infection is macerated in a reagent and a few drops of the liquid are placed in a well on the LFD.  If two lines appear in the window, as below, this indicates that a species of Phytophthora is present.

 

 

The material has to be sent for laboratory testing to identify the disease to species level.

Phytophthora ramorum, a notifiable plant disease, has been found on Rhododendron to the north of the Cannock Chase Country Park, and was originally suspected to be implicated in the dieback of bilberry.  It has not been isolated in laboratory tests but we cannot discount it as a threat to bilberry, which has been infected by it on one site in north Staffordshire.

Confirmed Phytophthora infections are generally restricted to the northern part of the Country Park, in and around Brocton Coppice, with several areas recently becoming infected to the south.  There is also evidence of separate fungal infections of bilberry on the open heathland.  The evidence currently available suggests that these infections are not killing the bilberry.

 

The threat to Cannock Chase

The Cannock Chase Special Area of Conservation (SAC) is of international importance for its heathland plant communities.  Bilberry, cowberry (Vaccinium vitis-idaea) and their nationally rare hybrid (V. x intermedium) are characteristic components of those communities, and the condition of the heathland would suffer substantially if they were lost.

Heather (Calluna vulgaris), the other key heathland component, and sessile oak (Quercus petraea), the dominant species in Brocton Coppice, are both potential hosts of Phytophthora species.  There is currently no evidence that they are infected, but if they were to succumb, the prospects for the Cannock Chase heathlands and ancient woodlands would be grim indeed.

 

The control strategy

Phytophthora spreads through producing spores - either zoospores which can 'swim' in films of water or long-lived resting spores known either as oospores or chlamydospores.  Zoospores can be spread in soil water, by rain splashing on infected leaves, or on the coats of animals that brush against wet infected vegetation.  Resting spores can survive for years in leaf litter and soil, and can be carried in mud on footwear, vehicle tyres and on animal feet.  There is no effective cure for wild plants infected with Phytophthora, so control measures have to be based on the destruction of infected plants through cutting and burning, and the prevention of the spread of spores.

Wild animals, horses, dogs and their owners are all potential carriers of spores.  Whilst we can do little to influence the movement of animals such as deer and badgers we can substantially reduce the risk by ensuring that we and our animals do not brush against infected vegetation or move mud around.   For this reason we are asking visitors to keep to the main tracks, not to stray into the vegetation, and to keep dogs on short leads at all times in the main affected areas.   The map below shows the areas where these access restrictions apply. The car park on Coppice Hill has been closed temporarily in the interests of disease control.

 Phytophthora Outbreak - Restrictions on Cannock Chase (Map)

The great majority of visitors are complying with these requests which are indicated on signs at the car parks, but a minority are not.  If the risk of the spread of spores cannot be controlled in this way the County Council may have to request Natural England to impose more stringent access restrictions on the Country Park.

The second aspect of the control strategy is the destruction of infected vegetation.  This is being done through mowing and burning of the cut material, but we are also experimenting with a heat treatment, to destroy infected plants without cutting.  This promises to be a faster method of dealing with infections in small areas, but the results may be unsightly.  Regrowth in the treated areas is showing signs of secondary infection from resting spores in the soil, so further treatments will be necessary to eradicate the disease.  We have the disadvantage that very little is known about the biology of this disease, because it has not been seen before on bilberry, so it is difficult to forecast the time needed to bring it under control. 

With thanks…

The County Council would like to thank all of the walkers, riders, mountain bikers, orienteers, bird watchers, dog owners and casual visitors who have heeded our requests to help control the disease.  Without your co-operation we would be forced to consider more stringent access controls.  Let us hope that it does not come to that.

Last Modified: 27/08/2009 07:46:29
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