Mystery Oak Disease pg.3
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.
