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Frequently
Asked Questions related to Sudden Oak Death
4
September 2002
Prepared
by the California Oak Mortality Task Force
What
is Sudden Oak Death?
It's a highly contagious disease that can infect and quickly
kill several species of native California oaks. It first appeared
in 1995 in Marin County and has since killed tens of thousands
of oaks and tanoaks along the state's northern coast.
What
causes Sudden Oak Death?
It's caused by a fungus-like brown alga called Phytophthora
ramorum (phy-TOFF-thoruh ruh-MOR-um), which was identified in
2000 by University of California researchers at the Berkeley
and Davis campuses. P. ramorum is related to the organism that
caused the Irish potato famine. It may have entered the U.S.
on imported nursery plants.
Does
this organism affect other trees and plants?
Yes,
it also has been found to be causing disease, similar to Sudden
Oak Death, in coast redwood and Douglas fir, as well as 14 other
plant species in the United States, including madrone, bay laurel,
buckeye and rhododendron. In Europe, it also has been found
in viburnum.
What
are the symptoms of Sudden Oak Death and related diseases?
In oaks, the first symptom is typically a bleeding or oozing
of thick, dark reddish-brown sap from the trunk. With tanoaks,
the first symptom is dropping of new leaf growth. Beetles then
attack the weakened trees, and in the later stages of decline,
decaying fungi are seen on the trunks of oaks and tanoaks. An
infected oak will form a girdle or ring of dead tissue beneath
the bark of its trunk, which blocks the flow of water and nutrients.
As a result, the tree may die in just a few weeks. Signs of
the disease caused by P. ramorum in redwood have been observed
only in the needles and very small branches of redwoods. In
redwoods, the infected seedlings became yellowed and discolored.
Douglas fir seedlings showed a similar, but more intense, response.
How
do scientists know that these diseases are caused by P. ramorum?
First they take DNA samples from trees to see if P. ramorum
is present. Then, in the laboratory, they see if they can cause
symptoms of the disease by infecting healthy seedlings with
that fungus-like organism. Where have Sudden Oak Death and other
P. ramorum diseases been found? These diseases have been identified
in trees and plants in Alameda, Contra Costa, Humboldt, Marin,
Mendocino, Monterey, Napa, San Mateo, Santa Clara, Santa Cruz,
Solano and Sonoma counties.
How
are Sudden Oak Death and related diseases spread?
P. ramorum, the organism that causes these diseases, is
spread via spores and cysts. During wet weather some affected
plants, such as bay laurels, release spores that can travel
in moist soil and through the air. People and animals can also
track spores to uninfected areas. Sometimes spore-containing
cysts form and accumulate in the bed of dead leaves beneath
the trees and can easily be spread by people and animals walking
underneath the trees. These spores and cysts also can be carried
in the plant material of dead hosts.
What
impact will these diseases have on California's landscape?
It is anticipated that Sudden Oak Death will spread to more
areas of California. Since various tree and plant species seem
to be more severely affected by P. ramorum than others, it may
take years before the full ecological impact of this disease-causing
organism will be known.
How
can Sudden Oak Death and related diseases be prevented?
Preventing the movement of infected leaves, wood and soil
is critical to slowing the spread of P. ramorum to other areas.
People who have been in infected areas should clean and disinfect
their shoes and vehicle tires with bleach. Chemical treatments
for preventing these diseases are being tested. Currently there
are no treatments approved for the prevention or cure of Phytophthora
ramorum.
How
is movement of tree and plant materials regulated?
The California Department of Food and Agriculture, the California
Department of Forestry and Fire Protection, and County Agricultural
Commissioners, in conjunction with the U.S. Department of Agriculture,
are responsible for enforcement of state and federal regulations
designed to slow the artificial spread of Phytophthora ramorum.
Where
can I get more information online?
Sudden
Oak Death Online Media Kit, UC Division of Agriculture and
Natural Resources
Marin County
UC Cooperative Extension Office
California
Oak Mortality Task Force
SOD Mapping Project
California Oaks
Foundation
Media
contacts:
Matteo Garbelotto, assistant adjunct professor of ecosystem
science and Cooperative Extension Specialist, UC Berkeley, (510)
643-4282, matteo@nature.berkeley.edu
David
Rizzo, associate professor of plant pathology, UC Davis, (530)
754-9255, dmrizzo@ucdavis.edu
Katharine
Facino, California Oak Mortality Task Force, (916) 651-9182,
katharine.facino@fire.ca.gov
Sarah
Yang, UC Berkeley Public Affairs, (510) 643-7741, scy@pa.urel.berkeley.edu
Patricia
Bailey, UC Davis News Service, (530) 752-9843, pjbailey@ucdavis.edu
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