|November 7, 2002
Volume 33 Number 6
|A publication for the faculty, staff, administrators, and friends of California State University, Chico|
Walk Softly in Coastal Forests
Sudden Oak Death infects entire ecosystems and is spreading
A festering epidemic in coastal woodlands continues to vex research scientists as it shows signs of spreading to the four compass points. It's caused by the fungal-like pathogen Phytophthora ramorum, whose popular designation Sudden Oak Death belies an adaptable and indiscriminate nature, said David Rizzo, a plant pathologist from the University of California, Davis and leading expert on the disease, during an hour-long lecture delivered in Holt Hall Friday, Oct. 25. The organism can harm any of 17 plants and trees that flourish within the coast's moist environment, including two that have prompted the lumber industry to sit up and take notice: Douglas fir and coastal redwoods.
"We found that this thing doesn't just infect oaks," said Rizzo. "Pretty much when you walk through the redwood/tan oak mixed forests in coastal areas in California and southern Oregon, just about every woody plant you see is a host of this pathogen. The only good news is that poison oak is on the list.”
Madrone, maple, coast live oak, toyon, bay laurel, rhododendron, and California buckeye are also targets of the infectious pathogen, which can spread by rain, wind, soil erosion, and even hikers’ shoes. One of about 60 species of Phytophthora, P. ramorum was identified two years ago by Rizzo and University of California, Berkeley’s Matteo Garbelotto as a new variant on an old problem: a Phytophthora was responsible for the Irish potato blight of the 1840s, while another relative within the past 30 years turned thousands of acres of Australian forest into grassland.
"The pathogen is here," emphasized Rizzo as larger-than-life withered tree images blinked by on the screen. "We're not going to get rid of it, so we must learn to manage it."
Sudden Oak Death infects patches of woodland from Big Sur north to Brookings, Oregon, and inland to Solano County. It's particularly virulent in Big Sur, where it has spread south through the canyons, and in Marin County's John Muir Woods. Earlier this year, maple leaves from the Sierra foothill community of Foresthill tested positive for the organism.
P. ramorum adapts readily to diverse environments, though it prefers the rainy springtime conditions ideal for its filament form, which feeds on plant tissue and creates reproductive sacs called sporangia. The sacs are filled with spores that can remain dormant in adverse conditions. Infected plant symptoms range from weeping cankers in trees to spotted and withering leaves in shrubs.
Eradication efforts are evolving as scientists learn more about the pathogen and test the potentials of fungicide and phosphate compounds. In an effort to prevent it from spreading, Oregon has opted for clear-cutting and burning isolated infected areas. Ongoing tests in this state indicate that composting can kill the organism. Meanwhile, European, Canadian, and U.S. governments have quarantined California nursery stock.
The Department of Biological Sciences and Omicron Theta Epsilon sponsored Risso's lecture.
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