A swimming, two-tailed fungus with an appetite for oak bark is probably to blame for the death of thousands of trees in coastal California, and if people aren't careful, the deadly microbe could spread to the nation's other oak forests, a UC Davis plant scientist said this week.
The fungi move around by spores that can easily travel in infected wood and soil, on bicycle and car tires, hikers' shoes and animals' feet, said UC Davis plant pathologist David Rizzo.
Rizzo is a member of the UC Oak Research Team that was assigned to track down and understand the killer of thousands of oaks in the past five years from Santa Barbara to Humboldt counties.
The team consists of research scientists from UC Davis and UC Berkeley, cooperative extension specialists and county farm advisors.
Rizzo said he released his findings in an attempt to raise public consciousness before the start of the rainy season, when the spores will be most abundant.
"Preventing the movement of soil and wood will be critical to slowing the spread of the fungus to other oak woodlands, such as the Sierra Nevada," he said. "In particular, firewood and soil should not be moved from coastal areas." Any wood already moved elsewhere should be burned.
Visitors to coastal forests should clean their tires, shoes and animals' feet thoroughly before leaving the area. Construction workers should wash equipment well and should not move dirt from one place to another.
Some infected oak trees may be able to be treated and saved, Rizzo said, but property owners should first be sure to have a sick tree diagnosed before beginning any treatment.
Rizzo's investigation showed that the culprit is a novel fungus related to the organisms that caused the Irish potato famine of 1845-50 and the modern deaths of Port Orford cedar trees in Northern California and southern Oregon, eucalyptus forests in Australia and oak forests in Mexico, Spain and Portugal.
It is a member of the genus Phytophthora (pronounced Phy-TOFF-thor-uh); the species has not been named or even fully described yet. It does not match any of the 60 known Phytophthora species anywhere in the world, Rizzo said. It is not known if the fungus has been recently introduced into California or is native and has only recently increased in importance as a tree-killer. Contrary to some Internet reports, the pathogen is not related to the oak wilt fungus (Ceratocystis fagacearum), an important disease of oaks in the eastern United States.
The fungus Rizzo isolated likes the cool, wet conditions typically found along much of the California coastline, especially in the redwood forests of the foggy coast ranges.
It cannot be seen unaided, but under a microscope, colonies of the fungus look like clusters of cotton fibers, he said. Those little creatures are highly fecund, he found; a single organism kept at 59 to 68 degrees Fahrenheit can produce thousands of offspring in 24 hours.
For more information about diagnosis and treatment, visit the University of California Cooperative Extension in Marin County Web site at http://cemarin.ucdavis.edu/index2.html.