Sudden Oak Death Strikes California Redwoods, Firs

BERKELEY, California, September 5, 2002 (ENS) - Sudden Oak Death, a swimming, two-tailed fungus that has killed tens of thousands of California oaks since 1995, has been discovered on California redwoods and Douglas firs.

The infected redwood saplings were found at Jack London State Park in Sonoma County and Henry Cowell State Park in Santa Cruz County. The infected Douglas firs were found at another site in Sonoma County.

The discovery of this fungus in California's redwoods, symbolic of the Earth's ancient forests, is disheartening for many people. The redwoods can reach heights of more than 350 feet and live to be 2,000 years old.


Redwood infected with the P. ramorum fungus (Photos courtesy Marin County UCCE)
The newly discovered fungus, named just last year, is called Phytophthora (Phy-TOFF-thor-uh) ramorum, meaning infector of twigs. True to its name, symptoms of the disease were detected only on the needles and very small branches of the infected redwoods.

That the cause of Sudden Oak Death was a new pathogen was established in 2000 by David Rizzo, a professor of plant pathology at the University of California Davis, and Matteo Garbelotto, a forest pathologist at the Department of Environmental Science, Policy, and Management in the School of Ecosystem Sciences at University of California Berkeley.

Rizzo, who isolated the new species for the first time, making diagnosis possible on a tree-by-tree basis, says the fungi move around by spores that can travel in infected wood and soil, on bicycle and car tires, hikers' shoes and animals' feet.

The fungus Rizzo isolated likes the cool, wet conditions found along much of the California coastline, especially in the redwood forests of the foggy coast ranges.

P. ramorum does not enter trees through the roots, but through the bark on tree trunks and limbs, possibly after they are splashed there by raindrops, Rizzo said. They have two propellant tails, called flagella, that send them swimming quickly through any water.

Once in the tree, the fungus produces enzymes that dissolve the dead outer and living inner layers of bark. Oozing sores result as the cell walls break down.

As the disease progresses into the wood, the tree becomes weak and vulnerable to bark beetles, which burrow into the tree and kill it by blocking its circulatory system.

Now that the Sudden Oak Death fungus has been found in coast redwood and Douglas fir, scientists have identified a total of 17 tree species that are liable to be infected by the Sudden Oak Death fungus.


P. ramorum in fir trees causes new shoots to wilt. (Photo courtesy )
Sixteen of them are found in California. The U.S. Forest Service identifies them as: California black oak, coast live oak, Shreve oak, tanoak, rhododendron, California bay laurel, big leaf maple, madrone, manzanita, huckleberry, California honeysuckle, toyon, California buckeye, California coffeeberry, and the Arrow wood which is found in Germany, the United Kingdom, and the Netherlands.

In May, the UK government placed a ban on imports of plants from California and Oregon and added controls on wood to protect Britain's beloved oaks from Sudden Oak Death, which has not become established in the British Isles. British plant health inspectors have found evidence of the disease in viburnum plants at a small number of nurseries.

Elizabeth Cole, a member of the Oak Mortality Task Force Management Committee and Restoration Subcommittee, says that scientists today agree that widespread treatment for Sudden Oak Death may never be available.

"The current approach to the epidemic emphasizes research to understand how the pathogen functions in the ecosystem, public education aimed at preventing human spread of the infection, safe removal of infected dead trees, monitoring, and possible reuse of the biomass," she says.

As the rainy season approaches, when the P. ramorum spores will be most abundant, it is important for visitors to coastal forests to clean their tires, shoes and animals' feet thoroughly before leaving the area. Construction workers should wash equipment well and should not move dirt from one place to another.

"Preventing the movement of soil and wood will be critical to slowing the spread of the fungus to other oak woodlands, such as the Sierra Nevada," Rizzo said. "In particular, firewood and soil should not be moved from coastal areas." Any wood already moved elsewhere should be burned.


An advanced stage of Sudden Oak Death
It is not yet clear how the disease will affect California's coast redwood and Douglas fir trees, which are ecologically and economically vital to the state, particularly to the timber, nursery, landscape and construction industries.

"Since we have not seen evidence of disease symptoms or death from the pathogen in large, mature redwood or Douglas fir, we cannot say what the effects of the infection will be long term," said Garbelotto.

"It may take years before we can start answering questions about the ecological impacts of the disease on coast redwood and Douglas fir," said Rizzo. The researchers emphasize the need for further study, noting that they have only been studying the biology of P. ramorum in redwoods and Douglas firs for several months.

This research was funded by the U.S. Forest Service Pacific Southwest Research Station, the Forest Service Forest Health Management and the Gordon and Betty Moore Foundation.

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