Last fall, Garbelotto noticed yellowed leaves on some California bay
laurels and a California buckeye on the campus and, after DNA tests,
confirmed the presence of Sudden Oak Death. A more complete survey of
the campus in November turned up 34 infected trees and shrubs, including
some at the world-renowned UC Botanical Garden.
No treatment or cure for the disease is known, but Garbelotto is at
the forefront of research to understand the disease and its host range,
and to find effective treatments.
"What we discover on the UC Berkeley campus is going to advance our
scientific understanding of the disease, determine the disease's host
range, and hopefully come up with a way to control it," said Garbelotto,
who is also an adjunct professor in UC Berkeley's Department of Environmental
Science, Policy & Management.
The campus has already formed an SOD Task Force and alerted the surrounding
community, including the City of Berkeley and the East Bay Regional
Parks, that the disease could be elsewhere in the East Bay. It's also
mounted an effort to educate campus groundskeepers, gardeners, arborists
and horticulturists how to recognize infected plants.
Once the campus survey confirmed Sudden Oak Death in the UC Botanical
Garden, director Ellen Simms immediately instituted a quarantine on
all plants and plant parts, stopping distribution to scientists and
arboretums and suspending the sale of plants to the public.
"The UC Botanical Garden is a museum of living plants, one of the
most diverse botanical gardens in the country," said Simms, associate
professor of integrative biology at UC Berkeley. "Sudden oak death could
profoundly affect the garden and its scientific mission."
Simms cautions that the disease is so new and so little is yet known
about it that the ultimate impact on the garden is impossible to predict.
The garden now has an important scientific role to play in clarifying
the host range of the microbe responsible for the disease.
"Not only does the pathogen infect an alarming number of species,
its hosts are taxonomically diverse, currently comprising 12 plant families,"
Simms said. "This broad taxonomic diversity suggests that the actual
host range is likely to be much larger. With its enormous taxonomic
diversity exposed to the pathogen at a relatively early stage in the
epidemic, the UC Botanical Garden will now play a significant role in
documenting the list of hosts."
While some hosts are very efficient at transmitting the pathogen,
others appear unable to do so. Research at the UC Botanical Garden can
determine which hosts are poor transmitters of the disease, and that
will help limit the number of plants destroyed in eradication efforts,
such as one underway in Oregon.
Also, because the garden holds plants from many habitats and continents,
research there could rapidly assess the world-wide taxonomic diversity
of hosts and put the garden in a position to provide Web-accessible
tools for identifying infections on these hosts.
"With this information, homeowners and other gardeners would be able
to identify infected plants, and those living in infested areas would
be able to make informed decisions as to which plants will best succeed
in their gardens," Simms said. "Knowing the host range will also help
to narrow the import restrictions that are being placed on California
plant and wood products by other states and countries."
The campus is responding in other ways, too:
* Signs are being posted to warn visitors that infectious spores may
be present, and cautioning them not to remove plant material from the
campus. Visitors also are urged to avoid muddy areas so as not to track
spores to uninfected areas of the state or nation.
* The trunks and lower limbs of all oak trees in the known infected
areas are being coated with a pesticide, copper sulphate, that Garbelotto
found could prevent the microbe from entering the oak. Copper sulfate
tree sprays are extensively used in organic orchards to treat fruit
and nut crops for a wide variety of tree diseases.
* Copper sulphate treatment of trees will be minimized and limited
to situations where they will have the highest likelihood of slowing
or containing the infection. Yellow flags around trees indicate they
have recently been treated with copper sulfate; they do not indicate
that the trees are known to be infected.
* The campus is prepared to treat oaks, should any become infected,
with a chemical fertilizer that has been shown to control pathogens
related to the one that causes Sudden Oak Death. The chemical, phosphonate,
would be injected into each infected tree just under the bark at the
base of the trunk to attack the pathogen systemically. While research
has not shown this can cure an infected tree, it may dramatically prolong
the tree's life and slow the production of spores that spread the pathogen,
Garbelotto said. The injections will be performed as part of a broad
series of experiments on disease control and are not available to the
public. He warns that the quality and efficacy of injection treatments
sold by private firms cannot be guaranteed at this point.
"We're staying the course," said UC Berkeley's SOD Task Force leader
Jim Horner, the campus landscape architect. "We are continuing to monitor
and treat trees on campus."
Called Phytophthora ramorum (fi-TOFF-thoruh ra-MOR-um), the Sudden
Oak Death pathogen is a member of the plant kingdom containing brown
algae and a relative of the microbe responsible for the potato blight
that launched a famine in Ireland 150 years ago. So far, it has been
found to infect at least 14 and possibly more than 20 different plant
species, though it apparently does not kill plants in all of those species.
Last November, after the disease was discovered at UC Berkeley, 172
plant samples were collected for analysis. Of the 102 plants samples
analyzed to date, 34 or one-third contained DNA of Phytophthora ramorum.
These included many bay laurels, a small number of tan oaks, sequoias
and California buckeyes, but no oaks.
The wooded UC Berkeley campus is planted with some 300 species of
trees, many dating from the 1870s and including between 800 and 1,000
coast live oaks.
The campus survey turned up potential new hosts, including the coast
redwood, Sequoia sempervirens. The pathogen was found on dying shoots
at the base of a redwood, but more tests must be done to determine if
the pathogen killed the shoots and whether it affects mature trees.
"We still need to confirm that Phytophthora is a primary pathogen
of redwood," said Garbelotto. "We have reason to believe redwoods are
a potential host, and we are doing experiments to see if they are."
If the redwood proves to be a host, the disease could have a profound
impact on the timber industry in California and the Pacific Northwest.
It also would broaden the host range of the disease from hardwood flowering
trees to the more economically important softwood conifers.