Then, on Tuesday, it was confirmed in a rhododendron at a nursery near a stand of infected live oak trees in Santa Cruz County. Rhododendrons, a popular ornamental bush, are sold at almost every nursery for commercial landscaping and backyard use. Since oak trees and rhododendrons generally thrive under the same conditions, researchers are afraid the disease could spread to oak trees around the world if measures aren't taken to stop it. The discoveries set off a near frenzy among scientists and state policy officials. A quarantine of oak firewood and possibly rhododendron plants remains a possibility in California, but state officials are reluctant to take such a step until the pathogen is better understood.
Researchers say there are still more questions about the disease than there are answers.
For instance, it is not known whether the Phytophthora spread from rhododendrons to oaks or vice versa. Garbelotto said, however, that rhododendrons were the more likely source because they are moved around so much and because many different Phytophthora s are known to attack them, providing a good environment for hybridization. Nobody knows whether the fungus has spread to other trees and plants, but the research team plans to test California's two native species of rhododendron as well as azaleas, a close relative. One curious fact is that the disease that kills oak trees does not seem to kill rhododendrons, but Garbelotto said that could be because nurseries often treated their plants with chemicals. The chemicals used on rhododendrons are now being tested, along with several other fungicides, in the laboratory to see whether they work on oak trees.