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Map of the Week: Killer fungus

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Mark Easton | 16:30 UK time, Monday, 8 December 2008

Rhododendron ponticum has emerged as public enemy number one in the fight against the misnamed "sudden oak death" fungus which, it is warned today, threatens to devastate gardens and parklands across the UK.

rhododendron image, courtesy of Scottish Natural Heritage
Image of rhododendron courtesy of Scottish National Heritage

The particular species of rhododendron was first introduced into Britain in the late 18th Century - loved by big country estates for its ornamental value and as cover for game birds.

But these days, R ponticum has few friends. It is already blamed for the destruction and abandonment of land - in the right conditions, it can grow to great heights and eliminate most native plants.

According to one group of countryside campaigners, "R ponticum destroys habitats and thus whole colonies of native plants and animals disappear."

Now it is accused of spreading two species of Phytophthora which, according to the National Trust and National Trust for Scotland, "could be in every garden in the UK within twenty years". The charities warn of the severe impact on our lowland and upland heath without a wholesale cull of the invader.

Defra map

My Map of the Week [click the link on the right] shows the government's latest published data on where the disease has been found and where it has been eradicated.

However, the latest maps do not include what the National Trust describes as a "deeply worrying development".

One species (Phytophthora kernoviae) has been found on bilberry on the Isle of Arran and at two sites in Cornwall.

According to the National Trust's lead advisor on the disease, Ian Wright, the discovery raises fears for the future of the UK's internationally important heathland habitats and for rare species including black grouse and capercaillie that the bilberry supports.

capercaillie rex features

Mr Wright said: "The fact that Phytophthora kernoviae has made the jump to heathland is deeply worrying."

What the maps do show is how incidences of the disease in the wild have been found in particularly large numbers in Cornwall (the suffix kernovia is derived from Kernow, the Cornish word for the region).

But virtually nowhere south of Hadrian's Wall is immune and it is now clear that Phytophthora has breached Scotland's defences.

Both the species of Phytophthora, kernoviae and ramorum, are fungal-like diseases which can kill plants like magnolia, camellia, kalmia and viburnum and, most commonly, rhododendron.

diseased rhododendron leaves
Image of diseased leaves from Defra website [138Kb PDF]

The National Trust and National Trust for Scotland have written to environment ministers in London and Edinburgh asking for cash so they can cull the Rhododendron ponticum that seems to be the main cause of the spread.

The Day of the Triffids comes to mind as one reads about disease-spreading R ponticum's move from gardens and nurseries into the countryside.

Its seeds are tiny and hence wind-dispersed. Each flower head can produce between three and seven thousand seeds, so that a large bush can produce several million seeds per year.

But established plants also spread by horizontal growth - a single plant may cover many metres of ground with thickly interlaced, impenetrable branches.

rhododendron image, courtesy of Scottish Natural Heritage
Image of rhododendron courtesy of Scottish National Heritage

Some 15 National Trust gardens have had outbreaks of the virulent disease - spread, it is thought, by the rhododendron. Four National Trust for Scotland gardens in the west of Scotland have also been affected.

Jan Haenraets, head of gardens and designed landscapes at the National Trust for Scotland, said: "Without concrete action the spread of these diseases poses a real threat to our native plant and species in our gardens, woodlands and heathlands. This would have a serious knock-on effect for the environment and local economies."

According to Defra, since the mid-1990s, the disease has caused widespread death of millions of trees in forest environments in coastal California and Oregon in the USA. Because the most commonly affected trees that have been killed are tanoaks (not true oaks) as well as several true oak species, this extensive phenomenon is commonly known as "Sudden Oak Death" in the USA.

NTPL handout showing the newly-arrived disease, Phytophthora ramorum, laying claim to a magnolia in Trengwainton Garden, Cornwall. NTPL/Stephen Robson/PA Wire

If you spot the disease you are encouraged to report it to the Plant Health and Seeds Inspectorate - if you follow the links here, you can find your local inspector to whom people can report any suspected disease outbreaks.

Update [15:55 December 9th 2008]:

kernoviae 3 maps

Hot off the press, Defra has sent me three new maps showing the spread of the Phytophthora fungus. They are still not up-to-date enough to include the outbreak on bilberry on the Isle of Arran, but are so new that they are not yet available on their website. I am delighted to offer loyal readers an "exclusive":
 • Phytophthora kernoviae outbreaks in UK
 • Findings of Phytophthora ramorum on plants growing in established gardens, woods and other wild sites in the UK 2002-2008
 • Findings of Phytophthora ramorum on plants at retail and nursery sites in UK 2002-2008

Update [15:16 December 12th 2008]: The maps above as originally posted had headings that were potentially misleading and have been replaced with better ones. And those who wish to see the situation in Scotland are directed to Garden/Wild Outbreaks of Phytophthora ramorum & Phytophthora kernoviae in Scotland [2.44Mb].

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