This page is dedicated to providing
information on the deadly new disease called 'Sudden Oak', which
now is threatening our shores. Contary to it's name it could
affect several species of our native trees.
Read on........ A
disease which has killed 80 percent of California's
tanoak trees has been found for the first time in several well
known British tree species, according to reports by the BBC,
New Scientist and U.K. Independent. Until November 2003 the
fungus, scientifically known as Phytophthora ramorum and informally
as Sudden Oak Death (SOD), had been found only in U.K. shrubs
and a tree native to the U.S. But the Forestry Commission says
the disease has now been found on beech, horse chestnuts and
holm oaks in Cornwall. There is no known cure for the disease,
which kills the trees' bark and is thought liable to affect
other species.
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The first signs of SOD may look
just like a small problem with the sap, but notice the
very much darker appearence, that looks as if it is
being eaten away
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More advanced stages of the
disease. Notice how the bark has been eaten away. This
continues until the tree is completely ring barked,
killing the tree
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Recently SOD has been discoverd in the UK bringing back memories
of Dutch elm disease, which wiped out 20 million of the U.K.'s
30 million elms in the 1960s. Sudden oak death was discovered
last year in viburnum plants in garden centres, since then there
have been more than 330 subsequent outbreaks in plant nurseries
and wild rhododendrons. However the disease did not appear on
a British tree until November 2003, when it was found on a southern
red oak in Sussex - a tree sadly imported from the US.
Unfortuantely it seems now it has surfaced several hundred
miles to the west, in Cornwall but Worse still, is the fact
that its latest victims include a native British species, the
beech, which is seen in much of the UK. One of the other infected
species, the holm oak, was brought here from Europe, and the
horse chestnut is also an introduced species.
The problem we face is that the disease may become endemic
in cultivated and wild woodlands, where it could be passed on
to established native trees such as the English white oak. "It's
obviously of considerable concern that we've found this disease
in mature trees. Our knowledge of it is fairly limited and we
cannot say what will be the full impact," said Stephen
Hunter, head of plant health at the Department for Environment,
Food and Rural Affairs (DEFRA). "We're still on a rather
steep learning curve in terms of understanding the disease's
biology and of how it will spread.
The disease was first spotted in Germany and the Netherlands
in 1993 but was restricted to the flowering shrubs rhododendron
and viburnum. It later turned up in California, where it has
attacked native tanoaks, coast live oaks and black oaks, killing
eight out of 10 trees.
It is now a fact that over 360 rhododendron and viburnum have
been diagnosed with the fungus in the UK since April 2002, although
most of the cases were in nurseries. (The import business being
a major concern) These same shrubs surrounded all four known
contaminated trees, affirming theories that the disease was
imported from nurseries in northern Europe and can spread through
shared groundwater.
"Fungicides do not destroy this disease, but they do suppress
it. It's a very uncertain threat and that's the problem. We're
working in an area of great uncertainty," Hunter said.
Shrubs carrying the disease around the infected trees are being
uprooted but the trees remain for study.
"Probably this disease did come into Britain on some material
from elsewhere, we don't know where from," Hunter said.
"We are proposing to increase checks at ports." Laboratory
tests have shown that beech, sweet chestnuts, sitka spruce and
Douglas fir are the native species most susceptible to infection,
although it is not possible to rule out risks to other seemingly
less-susceptible species, such as the English oak." he
said.
Chris Prior, head of horticultural sciences at the Royal Horticultural
Society, cautions: "We hardly know the fungus's full host
range, so the potential level of damage is much wider. We're
faced with a worrying scenario."The North American strain
of SOD is known to infect about 20 plant species, although the
severity of its effect varies by species. Prior says the Sudden
Oak Death name is misleading as trees other than oak are vulnerable.
"We're more worried about things like beech, which we suspect
will be more susceptible," he says.
Symptoms vary depending on the infected species. For example,
in the infected beech a 'bleeding canker' is oozing liquid from
a spot on the bark where the fungus entered the tree. Prior
says the tree will probably die.
"There's not going to be a cure in the
sense of a magic bullet," says Prior. Injections of fungicides
can provide temporary relief of symptoms, he says, "but
if the disease becomes established in the UK, treating acres
of trees is not an option."
First signs of disease on Maple leaf
The Forestry Commission hopes by April next year to have completed
a woodland survey to find out how far the fungus has spread.It
is important for anyone interested in conservation to be on
the lookout for the fungus it could prove vital in keeping the
disease at bay.Colin Morton of the commission said: "We
know it spreads from shrubs like rhododendron and viburnum to
trees, but we don't think it spreads from tree to tree. It seems
to be spread by rain splashing off the shrubs' foliage onto
the trees. Once on them, the fungus rings the bark all the way
round, letting sap ooze out and cutting off the tree's lifeline
so it will eventually die. There's no known treatment, but at
the moment we're not killing healthy trees near infected ones
to create a barrier. It may come to that, but we hope it won't."
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