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Here
in the 100th Anniversary year of the
 first detection of
the chestnut blight,
the tree that has
largely replaced it in the forests of the
southern
Appalachians is at risk for a similar fate.
Though
extinction of our oaks is neither certain nor
necessarily imminent, the threat is real enough to
have mobilized experts in the region and to have
garnered a $15.5 million infusion of federal
funding
to help make sure it does not become either.
“All words about
the American Chestnut
are now but an elegy for it. This once
mighty tree, one of the grandest features of
our sylva, has gone down like a slaughtered
army before a foreign fungus disease, the
Chestnut blight. In the youth of a man not
yet old, native Chestnut was still to be seen
in glorious array, from the upper slopes of
Mount Mitchell, the great forest below waving
with creamy white Chestnut blossoms in the
crowns of the ancient trees, so that it looked
like a sea with white combers plowing across its
surface. Gone forever is that day; gone is one
of our most valuable timber
trees, gone the beauty of its shade, the
spectacle of its enormous trunks, sometimes ten
to twelve feet in diameter. And gone the harvest
of the nuts, that stuffed our Thanksgiving
turkey or warmed our hearts
and fingers at the vendor’s street corner.… From
the time the blight was first detected, in 1904
in the New York Zoological Park, it spread with
a sickening rapidity. Crossing New Jersey, it
entered the great Chestnut stands of
Pennsylvania; that state, thoroughly alarmed,
appropriated a large sum
for the control of the malady, in which the
federal government joined. But all in vain.
Destruction of infected trees proved
ineffectual; new infections broke out at distant
points. For it was discovered that the spores
are carried far by wind, and the disease was
already scattered so far that quarantine lines
were futile.…Never again will those proud
forests rise.” —Donald Culross Peattie, “A
Natural History of Trees of Eastern and Central
North America”
I am sitting in an office in the
USDA Forest Service Southern Research Station in
Asheville, talking to an affable man with curly
gray hair and matching mustache whose name, all
too appropriately, is Steve Oak. A USDA Forest
Health Protection plant pathologist whose
specialty is oak diseases, Oak’s life has been a
blur of training sessions, conference calls and
task force meetings since March 9. That was the
day that the USDA’s Animal and Plant Health
Inspection Service (APHIS)
announced that
a huge Southern California wholesale
nursery had shipped plants to
customers all over the United States that might be infected with
the pathogen that has caused tens of thousands
of West Coast oaks and tanoaks to die. The pathogen, Phytophthora ramorum,
causes three diseases, two of them relatively
benign. The third is a killer known as Sudden
Oak Death (SOD). If unleashed in eastern
forests, SOD could cause an ecological disaster
as devastating as the chestnut blight. Sudden
Oak Death is something of a misnomer, as another
SOD researcher has observed, since the pathogen
or causal agent affects other species in
addition to oaks, since disease expression is
not always sudden, and since not every infected
tree dies. But it has become a major killer of
western oaks in less than a decade. P. ramorum
is a “new” pathogen, first detected in the
United States in California in 1995, and not
identified until 1999. Until this spring, its
range in the US – it is also present in Europe –
was thought to be confined to 13 central coastal
California counties and part of an Oregon county
near the California line. Quarantines prohibited
nurseries located in the infected counties from
shipping the pathogen’s host plants, which
include rhododendrons and other ornamental
shrubs, out of state. But Southern California,
the location of the Monrovia nursery that
shipped the suspect stock, was outside the
quarantined area. By the end of March, when
APHIS expanded the quarantine to cover all
California nurseries, P. ramorum had escaped its
former bounds.
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Within days
of the March 9 announcement, laboratory tests
showed that infected stock had indeed made its
way to the East. By May 13, with testing still
incomplete, stock shipped by Monrovia and
Specialty Products (another Southern California
mail order business) to 118 nurseries and garden
centers in 14 states – including North Carolina,
Tennessee, Maryland, Alabama, Virginia and
Georgia – had tested positive for P. ramorum. By
that time too, Oak, in his capacity as technical
coordinator of the National SOD Detection
Survey, had held three training sessions – one
in New England, one in the Midwest and one in
the Southeast – for state cooperators who are
conducting surveys involving 11 host genera this
summer, combing forests for SOD. The “soldiers
in the SOD army,” as he calls
them, are drawn from 35 states, most of them
east of a line from Minnesota to Texas. APHIS is
conducting a second national SOD survey – of
nurseries – looking for SOD-infected stock. On
May 18, Agriculture Secretary Ann Veneman
transferred $15.5 million in emergency funding
to APHIS for nursery inspection, sampling and
testing, SOD education and outreach. “We’re
operating in crisis mode now,” Oak acknowledges.
But it’s too early to assume that SOD will
devastate eastern forests, he says. Why? First,
because “while the pathogen that causes SOD has
arrived in the East, the killing disease has not
expressed itself here.” At least not yet.
Whether it will, no one knows – nor wants to run
a field experiment to find out. “There are a
range of possible outcomes in the East that run
from a chestnut blight-type scenario to
innocuous,” he says. “What’s hampering our
finding out is that this is a quarantined
pathogen that
requires a ‘containment greenhouse’ to study it
outside of the regulated areas on the West
Coast.” A containment greenhouse is a
hyper-controlled environment secure enough to
ensure that not so much as a single spore
accidentally escapes. There’s only one of these
facilities in the East – at Ft. Detrick, Md.
Steve Oak. The aptly named expert
says "it's virtually certain that infected
plants
have been planted in people's back yards."
Three years
ago, Oak provided specimens of 10 different
Eastern forest trees, 8 of them oaks, to a
researcher there named Dr. Paul Tooley, who inoculated
their stems and foliage with P. ramorum.
The results were bad news for eastern
species: all 10 developed symptoms of the
disease, though some were more susceptible
to the pathogen than others. Especially
ominous were results that showed that
chestnut oak – a member of the white oak
group – was the most highly susceptible of
all the tested species.
“The implications are that, unlike Western
white oak species which have been
unaffected by SOD, Eastern species in the
white oak group can be infected,” Oak says.
“In greenhouse inoculations, chestnut and
white oak were the most susceptible, followed
by northern red oak.”
Still, Oak cautions, what happens in the
laboratory may not occur in the field. Lab
conditions are tilted in favor of the
pathogen – the goal, after all, is to discover
whether it is capable of infecting a potential
host. Tooley directly introduced P. ramorum into stem wounds; he sealed
leaves into plastic bags containing P. ramorum
sporangia and
shook them up. In
the field, conditions
are more
haphazard. Spores
of P. ramorum may
land on the leaves
of a foliar host,
where they produce
blotchy
brown spots on
the leaves’ surfaces.
Those spots
are spore factories,
producing more
inoculum, which a
puff of wind may –
or may not – lift to
a nearby oak.
Some foliar hosts
produce more
spores than others.
“Apparently, it takes a lot of spores to
infect an oak,” he says, “We don’t know
whether we have the foliar hosts – the big
inoculum producers – in the East that will
create enough inoculum to infect our oaks.
That’s the big unknown in the East.”
But we do know that we have two of the
three necessary ingredients to produce
SOD: an abundance of host plants susceptible
to ramorum leaf blight and ramorum
shoot dieback, the two less-threatening
diseases.
In addition to the tests he conducted
on the 10 tree species, Tooley tested many
varieties of woody ornamentals that are
native – and common – to the Southern
Appalachians and Blue Ridge: mountain
and sheep laurel; flame, pinkshell and
smooth azalea; Carolina, Catawba and
Rosebay rhododendron; and dog hobble.
All proved susceptible to P. ramorum. And,
for most of the year, we have precisely the
kind of environment – cool and moist – that
P. ramorum requires to thrive.
Mabry Mill.
Rhododendron, azalea and oak's
susceptibility to
P. ramorum could change the look of one
of the
most-photographed spots on the Blue Ridge
Parkway.
And now we have
the pathogen –
thanks to interstate commerce and the
nursery trade. Since it’s airborne, and since
there are oaks and other hosts pretty
much all over the United States (though
deserts and the Great Plains are formidable
natural hurdles between California to
the East), P. ramorum might have reached
us on its own eventually. Ever since it was
identified as the killer of California’s oaks,
its potential for wreaking havoc in the
East has been a concern. In the fall of
2002, SOD began dominating Oak’s work.
Since March, it’s occupied 95 percent of
his time. Last summer he headed up a
seven-state pilot survey designed to
develop survey methods for early detection
of P. ramorum. Using USFS funds,
state foresters in Georgia, North and South
Carolina, Tennessee, West Virginia, Virginia
and Pennsylvania collected 10,000
leaf and oak bark samples from host
plants with P. ramorum-like symptoms. A
third of the samples came from the
perimeters of nurseries, two-thirds from
the general forest area concentrated in
high risk areas. The samples were tested;
all came up negative. Simultaneously, five
of the seven states conducted a nursery
survey, inspecting hundreds of thousands
of plants and collecting thousands of leaf
samples. Again, no positives turned up.
“The good news was that the techniques
used were good enough to detect
other Phytophthora pathogens common on plants, but no ramorum,” he says.
“The bad news was that it wasn’t a very
robust survey – only 10-15 nurseries per
state were sampled. Those surveys were
preparing us for the day that has now
arrived.”
Once
the discovery was made that
infected plants had been shipped outside
California, the wholesalers who shipped them
were required to provide a list of their
customers dating back to March 2003. Those lists
went to state agriculture departments who
notified nurseries and garden centers who might
have received infected stock, and
directed them to stop selling the plants.
Agricultural personnel visited each of the
nurseries, isolated the suspect stock and took
samples. If tests came back negative, sales
could resume. But a lot of them didn’t. By early
May, plants from 13 nurseries in Georgia and
eight in North Carolina alone had turned up
positive. (The numbers were lower for other
eastern states.) And those were from plants that
hadn’t already been
sold before the halt sale order was issued.
“It’s virtually certain,” Oak says, “that
infected plants have been planted in people’s
back yards.”
He hastens to add that
“introduction doesn’t mean establishment” of P. ramorum in the wild. “We think we have an
excellent strategy for dealing with the
situation inside nurseries that have received
infected or potentially infected stock,” he
says. “And we have a good strategy for
looking in places where the pathogen
might have moved, in the immediate
vicinity of those nurseries. But we’re
working feverishly now to try to reach
the back yards.” Cooperative efforts are
being launched by state departments of
agriculture, state universities and county
agricultural extension services to address
that problem.
“We have to get people trained,
get materials printed and into homeowners’
hands, come up with sampling kits and a way to
handle collected samples,” Oak says. “Our
strategy in the east will be
twofold: early detection, followed by aggressive
eradication.” A document to
guide the eradication effort is being
developed, based on the approach Oregon
– where SOD is present, but in a limited
area – has followed.
Why
so much effort to prevent a disease
that may not materialize? Or – conversely –
whose pathogen may already be incubating spores,
inoculating host plants, insidiously building to
critical mass in this yard and that
one, may already have spilled over into the
tangle of rhododendron, mountain laurel
and oak in nearby woods? The die may
already be cast for the trees whose name
Steve Oak bears. Trees that – in the 100th
anniversary year of the first detection of the
chestnut blight – occupy the niche vacated by
those vanished giants whose creamy,
blossom-studded crowns churned in the
wind like ocean waves. Not to make an
effort – which may be futile – can’t be an
option. As timber trees, as ecosystem
components, as providers of mast for
wildlife that once relied on burnished
nuts hidden within spiky green burrs to
make it through the winter, oaks are too
vital to eastern forests not to put up a
fight, if there’s a fighting chance, to protect
them from SOD. The losses, if SOD
gains a foothold in our forests, will be
staggering.
“In the West,” Oak says, “oaks are
islands in a sea of conifers. In the East,
oaks are the sea."
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