Oak Tree Fungus Found in Plants

A fungus that is killing oaks along parts of the California coastal region has been found in a common garden plant, further complicating efforts to contain the mysterious affliction and track its origins.

UC scientists announced last week that the organism responsible for “sudden oak death” had been detected in commercial rhododendron stock grown near some Santa Cruz County oaks dying of the disease.

The discovery establishes “another potential way the pathogen can get out of the area of infestation,” said UC Davis plant pathologist Dave Rizzo, one of the lead researchers on the fungus. “The big concern is that someone will transport a sick rhododendron to a place where there are susceptible oak species.”

The new development comes shortly after Oregon officials slapped a quarantine on nursery stock and wood products from the infected species.

The state is the first to take such action. Neither California nor federal officials have adopted regulations to stop the spread of sudden oak death, which has attacked tens of thousands of tanoaks, black oaks and coastal live oaks in six California counties.

Dan Hilburn of the Oregon Department of Agriculture said his agency imposed the quarantine because black oaks and tanoaks are found in his state and because the vulnerability of other oak species remains unknown.

“We’re protecting the rest of the oaks until it’s proven they’re not susceptible,” he said, adding that the Oregon restrictions would probably have little economic impact.

California officials say they don’t know enough about the fungus, a member of the genus Phytophthora, to adopt a quarantine.

“We’re looking to get better information. We don’t feel the threat is that imminent,” said Bill Callison, assistant director for plant health and pest prevention services in the California Department of Food and Agriculture.

The U.S. Forest Service asked the federal government last year to impose a quarantine on the interstate transport of affected products. The U.S. Department of Agriculture has drafted a quarantine proposal, but it is unclear when--or if--the regulations will be adopted.

Scientists concede that there are many unknowns concerning sudden oak death, which first appeared in California about five years ago in tanoaks. But they say it could take years to resolve them all.

“If we wait until we have every single answer, it may be too late to stop it moving to other places,” Rizzo said.

He and others also say they need far more funding to ascertain exactly how the fungus is spread and what plants are susceptible to it.

“The critical needs are the research needs,” said Susan Frankel, a U.S. Forest Service plant pathologist and chairwoman of a multi-agency task force on the disease.

There are several legislative proposals to appropriate millions of dollars to fight sudden oak death in California, but so far only about $200,000 in federal and state money has been spent on the effort.

The fungus, a relative of the organism that wiped out Ireland’s potatoes in the 1800s, has been confirmed in six counties from Big Sur to Sonoma County.

It was thought to be confined to the three oak species, but last summer scientists realized the fungus was identical to one found in some European rhododendrons in 1993. Then, last week, it was confirmed in the Santa Cruz nursery stock.

So far it has not been detected in European oaks.

The fact that the disease has only been found near the coast in California suggests there may be limitations on its range, but researchers note that the moist, wet conditions favored by the disease exist in plenty of other places.

Oregon’s emergency quarantine, imposed for three months, can be extended. The regulations say that nursery stock, firewood and wood products from affected species grown in the infested region can only be imported if they have been treated to kill the fungus.

Hilburn said his agency was particularly worried that infected firewood might be brought across the border in the winter season.

Given the uncertainties about how sudden oak death is transmitted, Frankel went so far as to suggest that the public simply not buy oak firewood.

Plant pathologists believe the fungus can move from one tree to another via rain splashes, but Rizzo said they are not sure whether it survives on firewood or in soil moved by humans or animals.

They do not know whether it traveled from Europe to California or whether the fungus reached both places from somewhere else. Nor do they know whether it spreads from rhododendrons to oaks or vice versa.

Dave Moeller, agriculture commissioner for Santa Cruz County, said he conferred with state officials last week and was told there are too many questions about the disease’s transmission to take any action restricting movement of the rhododendron nursery stock.

“We’re not going to take action until we have a sound biological basis,” Moeller said.

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Fungus Threat

A new disease is attacking three species of oak in Northern and Central California. Believed to be caused by a fungus, sudden oak death has so far been confirmed in six coastal counties--Monterey, Santa Cruz, San Mateo, Marin, Napa and Sonoma--and scientists are concerned that it may spread.