(LONG) PHYTOPHTHORA KILLING OAKS IN CA
truffler1635 at my-deja.com
truffler1635 at my-deja.com
Sat Aug 19 22:54:57 EST 2000
>From The Sunday Oregonian, Aug. 20, 2000, p A25
CALIFORNIAS OAK TREES FALLING VICTIM TO MYSTERIOUS DISEASE
Scientists are scrambling for answers as the deadly syndrome, first
noticed five years ago, spreads rapidly.
By CAROL KAESUK YOON, New York Times News Service
FELTON, Calif. - Despite the beauty of the towering redwoods and bay
trees in these mountains some 60 miles south of San Francisco, it is the
more modest tanoak trees that are everywhere dead and dying that draw the
Their sheaves of brown leaves a startling contrast to the verdant
forest around them these tanoaks, like thousands of trees up and down the
California coast, are falling victim to a new disease. Scientists call it
sudden oak death syndrome, and they are alarmed by its rapid spread and
its ability to kill an ever increasing number and variety of trees.
So many trees began dying this year that scientists began a mad
scramble to understand this syndrome, first seen five years ago in a
single patch of tanoak trees just north of San Francisco. In July,
researchers found evidence that the die-off -- which has spread to three
tree species -- had also spread over 350 miles along the coast from far
northern into central California, fueling concerns that the disease might
continue its rapid spread to other species and outside of the state.
Researchers became even more concerned last month when another team
of scientists discovered that the culprit appeared to be a previously
unknown species of Phytophthora, a notorious group of funguslike
organisms that includes a species that caused the Irish potato blight and
the species now killing oak trees in Europe and eucalyptus trees in
Weve never seen anything like this, said Dr. Rick Standiford,
associate dean for forestry at the University of California at Berkeley.
Oak trees die, of course, but nothing to this extent. Knowing what Dutch
elm disease and chestnut blight have done to our forests -- chestnuts are
basically extinct -- hopefully that doesnt happen with oaks.
A state of emergency has been declared in Marin County, one of the
hardest-hit areas, and a state-wide task force has been created.
While describing the disease as having reached epidemic proportions,
scientists note that there are still vast stretches of healthy oak trees
even in affected areas, though how long and how many of those will remain
healthy is impossible to predict.
Scientists are predicting, however, that the growing die-off will
have a huge impact on the thousands of animal species that rely on leaves
and acorns from these trees. Concern also is growing over the fire risk
posed by the rapid accumulation of dead trees in already fire-prone
areas. In addition, many homeowners are panicking over the loss of
beloved and valuable trees. In hard-hit and well-to-do Marin County, for
example, a coast live oak tree can add as much as $30,000 to the value of
Disease spreads rapidly
The disease was discvoered by Dr. Pavel Svihra, a horticulturist at
the University of California at Davis, in 1995 when he was called by
homeowners in the town of Mill Valley to inspect dying tanoak trees that
bordered their back yards. But for years he was unable to arouse the
interest of other scientists, who dismissed the problem as trivial.
Since then the disease appears to have spread rapidly, showing up in
a variety of forests, from tourist destinations such as Muir Woods
National Monument to remote wild lands to suburban back yards. And it has
jumped from attacking only tanoaks, a poorly regarded species, to
attacking prized coast live oak and black oaks.
The evidence was so overwhelming that something was going on, said
Dr. Brice McPherson, entomologist at the University of California at
Berkeley. People just couldnt ignore it anymore.
The first symptom of the syndrome is the so-called bleeding, as
wine-red sap oozes from the bark. Later the tree is attacked by beetles
that leave a coating of sawdust on the bark and by fungi, including one
known as Hypoxylon that sprouts black warty growths on the trunk. When
the tree eventually dies, its leaves go quickly from green to brown,
hence the name sudden oak death syndrome.
Are humans to blame?
Researchers still do not know how the disease moved from tree to
tree or forest to forest. But in the laboratory this summer, Dr. David
Rizzo, a plant pathologist at the University of California at Davis, and
colleagues discovered that the new Phytophthora makes a spore that can
swim. The finding suggests the disease could move in water as the spores
of other Phytophthora species are known to do. But the disease also could
have spores that are moving via soil, wind, beetle feet, hiking shoes or
tires. With the disease prevalent in state parks, neighborhoods and other
areas frequented by humans, some suspect humans are the real culprit.
How does it spread so fast? People visit Muir Woods, get it in the
tires of their car and drive back to Santa Cruz and bingo! said Dr.
Rizzo, whose laboratory discovered that the disease was caused by a
Phytophthora. Its scary.
Scientists noted that while disease-causing spores are likely to
spread far beyond California, they will cause trouble elsewhere -- on the
East Coast, for example -- only if tree species in the new areas are
susceptible and if the Phytophthora can withstand a variety of climates.
Researchers are testing both factors.
Scientists are still trying to determine just how far the disease
has spread and how many trees have been afflicted, with estimates ranging
from the thousands to the millions.
Dr. Maggi Kelly, remote sensing specialists at the University of
California at Berkeley, and McPherson are using aerial digital
photography to search for early signs of the disease. Stressed trees
often refelct light differently, and if these researchers can find such a
visual signature from the air, it would allow them to quickly do large-
scale surveys of the spread of the syndrome.
Impact could be big
Meanwhile, a team of six students working with Dr. Steve Zack, a
wildlife ecologist with the Wildlife Conservation Society based at the
Bronx Zoo, has done the broadest survey yet, individually examining 8,000
tanoak trees over a 350-mile span up and down the coast. They are finding
an average of 15 percent of the trees are infected across the range and
as many as 80 percent are infected in some areas.
The impact of all the mission acorns and leaves will probably be
huge, researchers said.
The cascading effect of losing these trees is going to be awesome,
Dr. Zack said. Were just waiting for the other shoe to drop.
It remains unclear why the disease is spreading now, whether it is
because this Phytophthora species is an exotic pest that has just arrived
or whether it is because the species is a formerly benign organism that
only recently evolved a virulent form. A few scientists are arguing that
the disease may be a long-standing but normally milder one that is
temporarily flaring up as it takes advantage of trees stressed by weather
or water conditions.
Far from having a cure, scientists say they are afraid that current
efforts to eradicate the disease may be doing more harm than good. For
example, some land managers and homeowners are cutting and uprooting
diseased trees. If the disease spores move in water or air or soil or via
the trees wood, such movement could accelerate the spread of the
Scientists also are concerned about the effect on the environment if
homeowners begin applying fungicide, which may not even affect the
disease, and insecticide, which is being used to keep the beetles at bay.
Just a few weeks ago, researchers were reluctant to make
recommendations because so little was known. The severeity of the
disease, however, is dissolving the hesitation of even the most cautious
researchers, as scientists have begun calling for action, including
quarantines on the movement of oak wood and living oak trees.
Theres so much we still dont know, said Dr. Susan Frankel,
forest pathologist with the Forest Service and chairwoman of the newly
formed California Oak Mortality Task Force. But we all agreed that we
cant wait any longer.
COMMENT BY POSTER: Any outbreak of Phytophthora should be considered very
seriously. An earlier outbreak of Phytophthora in wine grapes devastated
French viniculture from 1880-1920, and similarly adversely impacted the
fledgling US viniculture plantations. While I see no reference of
Phytophthora translation from oaks to wine stock from this article,
anyone interested in forestry or viniculture should continue to follow
this story as it evolves.
Posted as a courtesy by
Daniel B. Wheeler
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