Sudden Oak Death


It’s late afternoon on a beautiful California day near the San Francisco Bay, but the forest floor is dark – almost too dark to take pictures. Giant redwoods tower hundreds of feet overhead, their canopies partially blocked from view by a middle story of coastal live oaks and other broad-leaf trees. The massive boles of the redwoods, often 8 to 10 feet in diameter or more, combined with the strangely dim light create an other-worldly effect. It’s easy to see how George Lucas chose this alien landscape to film the final scenes of “Return of the Jedi.”

But my Star Wars fantasy can hardly last long here in historic Muir Woods amidst the dull roar of conversation in a dozen different languages. Rather than those cute little Ewoks that turned the final scenes of the first Star Wars trilogy into a high-tech muppet movie, the crowds consist of people from all over the world that have come to see the world famous redwoods.

I suspect I’m the only one here that has not come to see the world’s tallest trees, as impressive as they may be. Instead, I’ve come to Muir Woods to see the results of a scourge that has killed millions of trees all up and down the California coastline since it was discovered less than a decade ago. I’ve come to see it first-hand because many scientists believe that the spread of this scourge to the southern Appalachian forest could cause the greatest change to the forest since chestnut blight ravaged the eastern forest almost a century ago.

Sudden oak death: the name itself sounds sinister. And unlike the “dark side of the force,” this scourge is all too real here in Muir Woods. The many dead and dying oaks provide silent testimony to the potency of this new pathogen. It’s scientific name is Phytophthora ramorum and sudden oak death is only one of the symptoms it causes in trees and shrubby plants – the official list of species it infects is now over 70 and the list grows longer every month.

Depending on the plant species, P. ramorum infection may occur on the trunk, branches, or leaves. While many hosts, such as species of laurel, viburnum and rhododendron do not die from the disease, they do play a key role in the spread of P. ramorum, acting as breeding ground for innoculum, which then spreads to other hosts through wind, rain, and human activity. Of particular concern is peoples’ tendency to move plants from one place to another in the quest for an ever more exotic yard. In fact, it’s just that tendency – and the massive nursery trade that indulges it – that has brought P. ramorum to potentially thousands of yards across the Southeast.

According to officials at the U.S Department of Agriculture, hundreds of thousands of potential host plants from west coast nurseries that have since tested positive for P. ramorum have been shipped to nurseries in the Southeast. In the largest incident in 2004 (informally known as the “Monrovia incident” among state and federal officials after the California nursery supplier where the plants originated), nearly 50,000 potential host plants were shipped to the state of Georgia and more than 30,000 were shipped to North Carolina from infected nurseries. Officials guess that only about 1% of these plants were actually infected with P. ramorum, but the actual numbers will never be known – almost all were sold to homeowners and landscapers before they could be intercepted and there is no way to track them down.

That’s the bad news. The worse news is that nearly all experts agree the southern Appalachian forest is at extremely high risk for the spread of P. ramorum. According to Dr. Kelly Ivors, an assistant professor and extension specialist in plant pathology at N.C. State University, “The area around the Smoky Mountains is a very high risk area in terms of the presence of a lot of known susceptible hosts, favorable climatic conditions, and also in terms of the movement of infected plant material into the region.”

Ivors points out that the very biodiversity that makes the southern Appalachian forest so extraordinary, is also beneficial to the pathogen. “Oaks are a terminal host,” says Ivors, meaning that while the pathogen kills oak trees it does not reproduce on them. “It’s on the shrubby hosts like the rhododendrons, camellias and viburnums that the pathogen can produce innoculum and spread. And there’s a lot of those types of hosts in the Appalachian forest”

Every expert agrees that the southern Appalachians are at high risk for an epidemic, and the potentially massive consequences of a worst-case scenario are lost on no one. The question on all the experts’ minds is whether the pathogen has already escaped the yards and nurseries where it is known to exist in the eastern U.S. and is actually spreading through the native forests. Steve Oak, A USDA Forest Service plant pathologist based in Asheville, N.C., who coordinates the Forest Health Protection program on sudden oak death for the southeastern region is quick to point out, “ While the pathogen has been introduced into the eastern U.S., sudden oak death itself is not here.”

But others are a little more pessimistic. Dr. Howard Neufeld, a plant pathologist at Appalachian State University says, “there could be a long lag-time. The balsam woolly adelgid arrived around the turn of the century and wasn’t really noticed until the 60s and 70s when we started seeing widespread death of Fraser firs on our mountaintops. It’s only when we start to see massive death that we notice the problem.”

Don Rogers, who is the point person at the North Carolina Division of Forestry for sudden oak death, is coordinating surveys in natural forests in an effort to detect the pathogen. “It’s like looking for a needle in a haystack,” he says, even though his agency is specifically targeting forested areas near nurseries where the pathogen is known to have been introduced. Rogers believes that it will ultimately be up to the regulatory agencies such as the USDA, who inspect shipments of nursery plants coming into the region, to keep infected plants out. If the pathogen does escape into the wild, he says that the public will probably play the most important role in bringing the problem to their attention.

“We rely on the public to say ‘Hey, my trees are dying’,” says Rogers.

Both Steve Oak and Don Rogers point out, however, that it is not yet known whether the pathogen can even survive and spread under natural conditions in the east as of yet – it’s only been found in nurseries and a few yards.

Kelly Ivors holds out little hope for the “can’t survive in the eastern forest” scenario and believes it is probably just a matter of time before the pathogen is established in the Appalachian forest. Her experience in California, where she studied sudden oak death for her doctoral research at Berkeley, gives her grounds for a degree of optimism, however. She saw how management of the epidemic could contain its spread long after the huge extent and 650 km range of the epidemic closed off any options for prevention and eradication of the pathogen
“I don’t think it’s going to be the next chestnut blight,” says Ivors. “If you look at the epidemic on the west coast or areas in Europe where it’s already established, it’s been spotty – it isn’t spreading to every oak in the forest.”

James Johnson, who coordinates the sudden oak death program at the Georgia Department of Forestry, sees some hope in the strong federal and state agency response to the problem. “In Georgia in 2004 we had 14 nurseries with infected plants,” says Johnson, “and so far in 2005 we’ve had four. Maybe that’s a good sign.”

All agency officials and scientists seem to agree that the response of federal and state agencies has been extraordinary and unprecedented. “I am really impressed at how quickly the [federal and state agencies] mobilized resources to fight this epidemic,” says Dr. Neufeld.

But don’t look to the experts for any predictions on how the threat is likely to play out in the eastern forests; there’s just not enough information available yet to know.

“Personally, I don’t see another chestnut blight scenario, but that’s just my personal feeling and I’m an optimist,” says Steve Oak. “We simply don’t have enough information yet – the range of possible outcomes is huge.”

With the agencies doing all they can to stop the spread, it’s going to be up to the general public to help prevent sudden oak death from spreading into the eastern forest. Education, awareness of the problem, and the willingness of people to begin buying locally grown plants for landscaping rather than purchasing plants shipped from infected regions of the country may ultimately determine whether the forests of the southern Appalachians will face the “next chestnut blight.”

People who suspect they have found symptoms of P. ramorum on their property should contact their county extension agent. More information on sudden oak death and the symptoms and spread of the P. ramorum pathogen can be found at:

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