SHAREHOLDERSMystery oak disease may threaten nation's forests Pathogen that's killing Calif. trees on the move
By John Ritter
USA TODAY
SAN FRANCISCO -- On the rolling hills and low mountains of coastal Northern California, green and lush now after winter rains, live oaks, tan oaks, black oaks and madrones have been dying for more than two years. A mysterious microscopic organism that causes Sudden Oak Death has been found on a widening list of trees. Even the stately redwood, a California icon as well as a valuable timber product, may be vulnerable.
But a far more troubling scenario is gaining currency among plant pathologists and federal regulators: that the disease will make its way out of California and infect the forests of the interior USA with potentially disastrous results.
That seemed unlikely until the organism suddenly appeared last fall on a maple tree in the foothills of the Sierra Nevada more than 100 miles away. If confirmed by tests on more samples, that would mean it had somehow moved east from the Pacific Coast across the agricultural Central Valley -- signaling a highly aggressive pathogen capable of adapting to new environments and different trees.
Dutch elm disease and chestnut blight, scourges that virtually wiped whole species from the American landscape in the last century, began as localized infestations. ''Something like this could be transported on a piece of luggage from one place to the next,'' says Jim Skiera, associate executive director of the International Society of Arboriculture in Champaign, Ill. ''If it's as virulent as they say, it could be devastating. It could have a huge economic impact if it hit multiple species.''
Lab tests already have confirmed that the Sudden Oak Death pathogen, Phytophthora ramorum, kills northern red oak, the dominant hardwood in the U.S. timber industry and a preferred species in furniture, flooring, cabinets and architectural interiors.
The disease is getting researchers' attention across the USA, particularly where other varieties of Phytophthora infect native plants. ''It's certainly something that's not being ignored just because we're on the right coast,'' says Don Ham, professor of forest resources at Clemson University in South Carolina. ''Our oak species can be susceptible, and we want to be prepared.''
A federal quarantine ordered this month bans shipping soil and plants from more than a dozen host species outside 10 infected counties from Monterey to Mendocino and one Oregon county, Curry, that has a small infestation. Canada has gone further, prohibiting imports of soil and host plants -- those infected by the pathogen -- from anywhere in California. The state's $3 billion nursery industry complains that's overkill because the disease hasn't been found in most of the state, including Southern California.
But in Northern California, particularly hard-hit Marin, Santa Cruz, Sonoma and Monterey counties, it has spread unchecked. Sudden Oak Death -- it got its name before many non-oak hosts were identified -- first caused alarm on the slopes of Mount Tamalpais in Marin County north of San Francisco. From a distance, dead and dying oaks look like random clumps of yellow and gray on the forested mountainside.
An evergreen hardwood species that lives up to 250 years, live oaks are indigenous to 10 million acres of the Pacific coast, prized flora that add value and aesthetic charm to property. They generally grow 20 to 40 feet tall at elevations between 3,000 and 5,000 feet. Though they are commercially worthless except as firewood because of their gnarled, crooked trunks and branches, those same features create beauty and endless variation on the coastal terrain.
Homeowners are appalled watching their precious oaks die by the thousands. Once they notice the spiky roundish leaves turning yellow, the rust-colored spots on the bark and a sticky black ooze bleeding from the trunk, it's too late -- the tree's a goner.
So hard hit was China Camp State Park in Marin County that the state closed campgrounds for several weeks to cut and remove hundreds of dead trees. Santa Clara County will try to keep isolated disease pockets from spreading by posting signs in parks asking bikers, hikers and horseback riders to clean soil off their vehicles and possessions when they leave. Officials worry that dead trees piling up will heighten the fire hazard during California's long dry season. Hard-hit composting companies -- a $200 million-a-year statewide industry -- can't ship goods from quarantined counties.
Disease's origin stumps experts
Sudden Oak Death is considered a formidable pest even for California, which spends $27 million a year controlling the fruit- and vegetable-eating med fly and has raised $50 million to fight the glassy-winged sharpshooter, a leaf-hopping insect that preys on grape vines.
The federal government has allocated $85 million for Sudden Oak Death research, but scientists still don't know how or where the disease got started, precisely how it spreads or how to eradicate it. They do know that once Phytophthora ramorum spores penetrate bark in the trunk, the organism eats away the cambium, a layer of tissue that conducts nutrients through the tree, in a matter of months. By tree-disease standards, that is an unusually short time.
Scientists are racing for answers on several fronts. They're trying to understand the biology and genetics of Phytophthora ramorum. They're studying whether pollution or short-term climate changes might have sparked the disease. They're looking at how the disease fits into the forest dynamic, whether animals and other plants play a role. Because oaks are popular trees in residential areas, humans may be a factor, through pruning and other tree-management techniques.
The disease has surprised researchers at every turn. At first they couldn't figure out how it spread from oak to oak. Other known Phytophthora species live in soil and attack trees at their roots. But trees suffering from Sudden Oak Death had no root damage. Eventually they discovered that other trees -- bay laurels, maples, buckeyes -- were infected and spreading Phytophthora spores through the air. Azaleas and rhododendrons are also hosts.
It was a brand new species of Phytophthora, never before identified, airborne and aggressive, with no known natural enemies. ''For the first time we have an organism that can infect a broad host range of plants in this country, with a biology that's completely unknown,'' says Matteo Garbelotto, a forest pathologist at the University of California-Berkeley. ''It's like all of a sudden finding a very poisonous snake that can fly.''
Garbelotto and another scientist, David Rizzo at the University of California-Davis, are the first to use DNA technology on a new forest disease. They isolated Phytophthora ramorum's DNA, tested hundreds of samples for its presence and identified 14 hosts in just 18 months, a process that would have taken years under conventional plant-pathology methods. More hosts are likely to be identified.
They've probably slowed Sudden Oak Death's spread because their findings allow state and federal regulators to act quickly to ban movement of additional host plants from nurseries. The scientists have asked the U.S. Energy Department to fund gene mapping of the pathogen.
But what eludes them is a cure. In the lab they're studying organic chemicals, biological compounds that might prevent infection by Phytophthora spores. They're testing different types of protective trunk coatings that could be applied to a tree. They're also trying to develop ways to boost a tree's own defensive response. But nothing yet has proved a magic bullet. Another option is simply removing host species like bay laurel from the forests, but that could have unknown effects on an ecosystem.
Knowing where Phytophthora ramorum came from would help, but that, too, remains a mystery. It could be an exotic organism, accidentally introduced from a locale where native plants have resistance to it. Once here, it feasts on hosts that have no defense. It could be a new species produced by genetic change, a hybrid with a potent effect on oaks. Or it could have been present all along, benign until an unknown factor caused it to become destructive.
Some speculate that several wetter-than-normal winters are linked to the emergence of Sudden Oak Death. The pathogen is a fungus-like organism similar to algae that thrives in moist conditions. Others think pollution is a culprit, but Garbelotto discounts that. He says environmental factors could have sparked change in the pathogen, but he sees little evidence that they weakened the oaks.
''I don't buy the direct relationship to pollution,'' he says. ''We can infect very healthy trees and still kill them.'' The disease has not wiped out whole forests, and Garbelotto believes many coast live oaks may have enough tolerance to survive the pathogen.
Redwoods may be endangered
Unknowns puzzle the scientists, chief among them how far the disease will spread and what other species might succumb to it. The discovery of spores on redwoods is particularly sensitive in California, where giant redwoods are a major tourist draw and redwood timber is a $500 million-a-year industry.
Spores could have been splashed on a few redwoods and they'll have no effect. Or redwoods may turn out to be hosts. In the worst-case scenario, the trees are susceptible to the disease. Garbelotto and Rizzo are trying to infect mature redwoods with Phytophthora ramorum to see if they're susceptible. Test results won't be known until later this year. ''At this point we have no evidence to suggest the disease affects the big redwoods,'' Garbelotto says.
If redwoods come under quarantine and lumber must be treated to get rid of the pathogen before it can be shipped, those pricey redwood decks will get even pricier, and small timber companies would suffer.
''It could be an economic disaster for a lot of people. It could potentially put us out of business,'' says Bud McCrary, co-owner of Big Creek Lumber Co. in Santa Cruz. ''How would you show that that particular lumber doesn't have any of those spores?''
An even more intriguing question is whether Phytophthora ramorum has migrated or been carried to the Sierra Nevada. Scientists need more than a positive DNA sample from a single tree to confirm that it has. Garbelotto is eager to collect more samples when the snow melts in the mountains.
All bets would be off if the pathogen is confirmed there in a climate wholly different from the coast. One of the West's major ecosystems could be threatened. And the theory that the disease might be incapable of wreaking harm in a new environment would be open to doubt.
''We saw Dutch elm disease devastate America's elms. We saw the same thing with chestnut blight years ago,'' says John Rosenow, president of the National Arbor Day Foundation in Lincoln, Neb. ''Oaks are such an important tree nationwide that we certainly hope scientists can isolate it to a small area.''Cover storyContinued fromCover storyCover storyCover story
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