Hardy Pathogen Cutting Down Pacific Oaks    Eleanor Tillinghast
   Jan 19, 2004 07:46 PST 
Hardy Pathogen Cutting Down Pacific Oaks
Scientists' Hopes for Pesticide Are Tempered by New Strain of Disease

By Garance Burke
Special to The Washington Post
Monday, January 19, 2004; Page A08

MARIN, Calif. -- For eight years, a mysterious pathogen called sudden
oak death has eluded researchers as it has killed off thousands of oak
trees along the California coastline. The highly contagious disease,
which causes trees to develop blood-colored oozing cankers before they
dry up entirely, has spread through state parks and private ranches
alike, and it now covers one-fifth of the California landscape.

Last fall, when scientists released a pesticide that can inoculate the
trees against the infection, authorities hailed it as an important
victory for western forests. But the discovery of a second strain of the
disease on a potted plant in a Portland, Ore., nursery has sparked fears
that the blight may prove to be resistant to the treatment, posing an
even greater scientific challenge.

"What happens when something of this size hits in the public health
field? You get an international outcry about SARS," said Matteo
Garbelotto, the University of California at Berkeley plant pathologist
who first identified sudden oak death in 1995. "But when an
environmental crisis of this scope hits, no one pays any attention -- it
flies under the radar. Something similar to this happened with Dutch elm
disease, and the one that really wiped out all the elms was the second

Garbelotto, who developed the phosphate-based pesticide, has been
training California tree experts how to combat the disease with plastic
syringes and power drills. Straun Edwards was one of 60 arborists who
gathered recently on a dry hill north of San Francisco to learn how to
vaccinate trees against the funguslike pathogen.

"People just don't know what to do when they see a 200-year-old tree
wither up and die in a period of a few weeks," said Edwards as he strode
along a dirt path that revealed vistas of the oak woodlands below.
"Sudden oak death was starting to affect business, because my customers
would be, like, 'I don't care what it costs; just save my tree,' and I
would have to be, like, 'I'm sorry; I can't.' Now at least there's
something I can do."

Plant pathologists first discovered the organism in an oak grove in the
Marin hills, just a few miles from the site of the workshop. After
mapping its DNA, they named it Phytopthera ramorum and concluded it was
a relative of Ireland's potato blight. With sudden oak death -- as it is
commonly known -- now turning up in forests in British Columbia and the
Netherlands, scientists are increasingly concerned about the long-term
effects the disease may have on forest ecosystems.

Sudden oak death spreads through airborne spores, which typically form
on bay leaves and then disperse onto oaks, redwoods, firs, madrones,
evergreens and other species. Once infected, the trees develop the
telltale oozing cankers, and their canopies quickly turn from green to
brown. After that, hordes of bark beetles attack the trees and weaken
their vascular systems so significantly that the trees can topple in
strong winds.

The devastation is clearest in the area around majestic Big Sur State
Park, just south of Monterey Bay. Long renowned for its granite cliffs
and 1,000-year-old redwood trees, Big Sur closed several of its canyon
trails last year when park officials realized campers could be hit by
falling timber. Several paths are lined with groves of gray, dying tan
oaks, and rangers have put up signs warning park visitors to wash their
boots and tires with Lysol to keep from bringing the spores with them.

In infested areas such as Marin, authorities are also concerned that
Phytopthera ramorum is increasing the amount of dry fuel on the forest
floor, said Steve Jones, California's deputy chief for forest pest
management, who helped fight last year's San Diego area wildfires.

"Sudden oak death is not . . . like an insect, where you can track it,"
Jones said. "It's this invisible thing that's causing infections, and
we're going to have to live with it. Ultimately, what we'll be doing is
managing the forests for the disease to minimize the impacts."

Yet for arborists such as Edwards, who tends infected trees along
California's central coast, the advent of the pesticide was a milestone.
Until last October, the state had refused to certify a dozen suspect
cures that were being marketed to desperate homeowners.

"You notice I'm hugging this tree?" Doug Schmidt, a UC-Berkeley
researcher, asked as he measured the circumference of one giant oak by
wrapping his arms around its trunk. "First thing you want to know is how
much pesticide you're going to inject into the bark after you've drilled
your hole. Then you take your syringe out."

The state-certified phosphate-based treatment works by penetrating the
cambium, the layer between the bark and the wood core that is most
affected by the disease, Schmidt told the arborists. Once the liquid
moves past the inner bark layer, the oak tree starts releasing chemicals
to fight off the infection, much the way a vaccine engenders immunity in
the human body. Tree experts can encourage the tree's resistance by
spraying it with a topical application of the pesticide and by following
up with seasonal "booster shots."

But the Australian-manufactured treatment has limitations: Costs prevent
it from being used to treat whole forests, and the chemicals cannot
counter sudden oak death's ability to lie dormant in hosts as different
as potted rhododendrons and giant redwoods.

"This is a big step forward for saving individual oak trees and all oaks
that act as hosts. But beyond that, it's not clear how much of it is
inherited in the seedlings," Garbelotto said. "All this does is mask the
symptoms, but they can still move around."

In an attempt to halt the spread, federal and state authorities have
sunk more than $20 million into research and regulatory oversight of
hazardous materials in the past four years. Because Garbelotto's lab
confirmed that 37 different plant species can act as hosts for the
disease, the U.S. Department of Agriculture's Forest Service has been
investigating whether the pathogen (in either of its mating forms) could
attack eastern black oaks and pin oaks.

Last summer, the Forest Service conducted a survey in Virginia and six
other eastern states to determine local species' vulnerability to the
blight. It took several months for the insect and disease specialists to
sample enough ornamental shrubs and mountain laurels to come to a
judgment, but in October they determined that no symptoms of sudden oak
death have been detected on the East Coast or in the Appalachians.

"In all fairness, we don't really know what we would do if it were
introduced into the East," said Steve Oak, the Forest Service
pathologist who coordinated the survey. "It's not a foregone conclusion
that it would be an apocalypse, but this is really not something we want
to learn about as a consequence of it showing up."

Re: Hardy Pathogen Cutting Down Pacific Oaks    The Darbyshires
   Jan 19, 2004 13:34 PST 
Interesting article - thank you for sending it out. There are some details
that the article doesn't mention. One is that not all species affected by
this disease are killed by it. Some only experience leaf discoloration
and/or tip dieback. Tanoak (Lithocarpus densiflorus) and coast live oak
(Quercus agrifolia) and a few other species are killed, and these are the
species that form the cankers referred to in the article. Others, such as
myrtle (Umbellularia californica) and Pacific rhododendron show dead spots
on the leaves, and yet others, such as redwood, Douglas-fir, and evergreen
huckleberry, show tip dieback. Most of the species affected have evergreen
leaves/needles. There are websites that list susceptible species and the

The strain (genotype) of the disease found in a nursery in Oregon was found
to be more similar to the strain that originated in Europe vs. the
California strain. The plant material that the European strain was found on
in Oregon came from Canada, and before that, I believe, it originated in
Europe. It's amazing how nursery stock moves around. It is a credit to the
Oregon State Dept. of Agriculture for their surveillance/testing program
that the disease was found in that nursery near Portland. All of the plants
of that genus and from that source were tracked down and destroyed. There
have even been followup tests to ensure that the disease is gone. The
current thinking is that the disease originally came into the US on nursery
stock (probably rhododendrons) that was imported into the California bay
area, and the disease spread into the forest from there. Apparently that is
fairly common/typical for Phytophthora diseases, and easily preventable with
fungicide applications. Many of the Phytophthoras are spread in soil/mud,
and some, like sudden oak death and potato blight, appear to be spread
through the air.

It is also interesting that the infection pathway mentioned in the article
(myrtle as the spore producer) is not occurring in southwestern Oregon, and
generally only shows up in California after the disease has been present in
the area for several years. In fact, the longer the disease exists in an
area, the more species infected.

Since the disease spreads in soil, water, and bark, when it infects a
forest, it has a big impact on movement of forest products and non-timber
forest products. Trees of susceptible species have to be debarked before
they can be removed from the area, and harvesting of non-timber forest
products of susceptible species is prohibited if they will be removed from
the quarantine area. Washing of vehicles, equipment is also required.