Like a plague from a horror film, the fungus attacks an oak's leaves, branches and trunk, causing open wounds that ooze a blood-red fluid. Foliage wilts, insects attack the dying limbs and a decades-old tree is dead in a matter of weeks.
It's called sudden oak death, and it has killed thousands of oaks on the Pacific Coast, infected dozens of other plant varieties and -- scientists and horticulturists fear -- could be making its way to the East.
Although the disease has not been found in the wild here, it has shown up on a rhododendron in a retail garden center in Maryland.
In Virginia, one nursery was exposed to sudden oak death from stock shipped from a nursery in California, the state most afflicted with the fungus.
Last month, plant pathologists and ecologists in Maryland circulated an e-mail update reporting that 108 nurseries in 13 states had found plants that tested positive for sudden oak death. In late April, the Animal and Plant Health Inspection Service of the U.S. Agriculture Department placed restrictions on interstate shipping from California of plants known or suspected to harbor the blight.
"You can't look at an oak tree and start worrying -- luckily it isn't to that point," said Carole Bergmann, forest ecologist with the Maryland-National Capital Park and Planning Commission. Nonetheless, "we should take it very seriously."
First identified in 1995 by Matteo Garboletto, a plant pathologist at the University of California at Berkeley, the sudden oak death fungus, called Phytophthora ramorum, is a genetic cousin to Irish potato blight. Besides oaks, it has been known to attack redwoods, evergreens and flowering trees. Scientists in California are experimenting with inoculating trees against the disease, but the blight has shown signs of mutating, complicating their efforts.
At Fort Detrick in Frederick, the USDA Agricultural Research Service's Foreign Disease-Weed Science Research Unit has been testing the disease on a variety of trees found in this region, including ornamental plants such as rhododendrons, azaleas and camellias.
Because the blight is so contagious researchers work in a highly protected laboratory and wear spacesuit-style gear and respirators. Some of the plants they have tested have proved susceptible to the disease. But what researchers do not know is whether sudden oak death spores can survive in the mid-Atlantic climate. In areas of the Appalachians the climate is quite similar to that in the foggy Pacific coastal regions where the disease has decimated swaths of trees.
"Nothing's been found in the wild in the East," said Douglas G. Luster, research leader at the USDA facility in Fort Detrick. "But we're worried."
Adding to the uncertainty, researchers say, is that the pathogen does not behave the same way in every plant and that some plants are more susceptible than others. In large tree species, the fungus enters the cambium, the circulatory system of the tree just beneath the bark. In oaks, it destroys the cambium, interrupting the flow of nutrients and killing the tree. Yet other plants appear able to survive the blight.
For example, mountain laurel, common in the Appalachians and sold widely as a landscape plant in this area, is very susceptible to sudden oak death, Fort Detrick research has shown. When exposed to the fungus, mountain laurel does not develop the trademark oozing cankers. Instead, the fungus causes large splotches on the leaves and wilting of some young twigs. Yet the plant does not die immediately. Whether it would die over time is still being investigated.
These different rates of infection raise worries in some states that the blight may be able to lie dormant in some plants, making them carriers that could escape detection.
Officials in this region need no reminders of the damage epidemics can do. Blight wiped out billions of American chestnuts in Appalachian states in the first half of the 20th century; Dutch elm disease attacked millions of trees in the second half.
The California Oak Mortality Task Force, a consortium of scientific and government experts convened to work on the disease, circulates a list of about 60 plant types susceptible or believed to be susceptible to the disease, including Douglas fir, witch hazel, California buckeyes and bigleaf maple. More plants are added regularly.
As a first step, "people should understand that there are other host plants" besides oaks, Bergmann said. But what nobody knows, she said, is "which plants hold the pathogen" and could spread it years from now.