Once again, there is a fungus among us, one that has the grim potential to bring the mighty oaks of the Eastern forests crashing down.

The aggressive and virulent fungus that causes sudden oak death showed up in the United States in coastal California and Oregon in 1995. It recently was discovered in contaminated host plants that a Los Angeles wholesale nursery unknowingly shipped to every state.

The fungus attacks oaks through their bark, causing girdling of the trunks, bleeding cankers, crown dieback and eventually death of the tree. There is no known cure.

Until now, it has been confined to the West Coast, where it has devastated hundreds of thousands of northern California's prized, majestic, coastal live oaks, as well as black oaks and tan oaks.

If the fungus gains a foothold in the Appalachian Mountains, especially in areas where conditions are cool and damp enough for it to thrive, it could change the nature of Eastern forests like nothing since the fungal blight that all but wiped out the then-dominant American chestnut tree in the first half of the last century.

It could be as bad as or worse than Dutch elm disease, a fungus that reached the United States in the 1930s and killed between 35 million and 70 million trees.

"I think this is a very serious threat. It's the scariest thing that I've seen in my lifetime," said Kurt Gottschalk, project leader at the U.S. Forest Service's research laboratory in Morgantown, W.Va.

"The Eastern forests have been fairly resilient, even though we have lost species with the invasion of the chestnut blight, the butternut canker and Dutch elm disease. We're fortunate to have a lot of tree species, but they've been getting picked off one by one."

That reduced diversity makes the Eastern forests more likely to be damaged by exotic pathogens such as sudden oak death, Gottschalk said.

Not all Eastern oak species are susceptible, but those that face the highest mortality include Pennsylvania's most common oak species, the northern red oak; the state's third most common variety, the black oak and the northern pin oak.

The U.S. Department of Agriculture issued an alert late last month that prohibits the Monrovia nursery, one of the nation's largest plant wholesalers, and 1,500 other nurseries in California, from shipping host plants until they are inspected and certified to be free of the fungus.

Nurseries in the east that received shipments from Monrovia, including one in southeastern Pennsylvania, have been ordered to stop selling and destroy the plants by the U.S. Department of Agriculture. According to the USDA's Animal Plant Health Inspection Service, the infected plants include several varieties of camellia.

The fungus, Phytophthora ramorum, which wasn't positively identified until 2000, five years after oak species north and south of San Francisco started dying, also infects but doesn't kill at least 59 host plants, including arbutus, bay laurel, huckleberry, madrone, bigleaf maple, California buckeye camellia and rhododendron.

Thomas Hall, a plant and forest pathologist in the state Bureau of Forestry's Division of Forest Pest Management, said the fungus could cause damage to many of the 38 oak species in the East.

"I think the pathogen is highly virulent. If it does get established, we could see some oaks succumb very rapidly," Hall said. "It has the potential for doing a lot of damage to the Eastern forests. I'm not saying it will be as devastating as the chestnut blight, but it could be. We don't know."

The fungus favors cool, moist climes, making the central and southern ranges of the Appalachian Mountains, including those in Pennsylvania, prime territory for its spread.

Hall said that Pennsylvania, like West Virginia, Virginia, Tennessee and Kentucky, is working with the U.S. Forest Service to set up study plots in forested areas and adjacent to some large nursery operations to monitor forest health and test for sudden oak death.

Some plots were established last year and 26 more are planned this year. None of the plant material sampled in Pennsylvania last year tested positive for the fungus.

"Because human commerce has developed worldwide, there's a reasonable chance that this could be introduced into eastern North America," Hall said. "Fortunately, it won't eliminate every oak tree, but we will go through a traumatic period if this thing gets loose."

California nursery plants shipped to Florida have already tested positive for the fungus. Plant shipments to Georgia and Maryland have shown signs of the fungus, but laboratory tests will not be final for several days.

In Pennsylvania, the only known shipments from Monrovia's California nursery were camellias sent to a nursery in the southeast, said Nancy Richwine, a plant pathologist with the state Department of Agriculture's Bureau of Plant Industry.

The state put a "stop sale" order on all the plants and ordered them destroyed, but some could have been sold before that order.

"If a retail outlet has information on such a sale, we would try to track the plant, but 99 percent of the time, they wouldn't have that information," Richwine said.

Because only one of the state's 5,000 nurseries, greenhouses and plant retailers received plant materials from Monrovia before shipments were suspended in March, Richwine said, the risk doesn't warrant statewide notification or a prohibition of plant imports from infected areas of California and Oregon.

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Don Hopey can be reached at dhopey@post-gazette.com or at 412-263-1983. Copyright (c)1997-2004 PG Publishing Co., Inc. All Rights Reserved.