Oak disease poses new threats. (News from the World of Trees).

At first it seemed like the ebola of oaks--new, sudden, virulent. Oozing reddish-brown sap announced the mysterious killer's presence, then the tree's entire crown wilted and, seemingly overnight, it died. But as its range of victims grows, sudden oak death (SOD) is revealing itself to be a highly complex adversary. Should it spread widely, it could provoke ecological and economic angst of continental proportions.

Besides its original victims along the California coast--coast live oak, tanoak, and California black oak--SOD sickens or kills an array of species ranging from California buckeye and bigleaf maple to evergreen huckleberry and bay laurel.

Indeed, by the time this issue reaches your hands the magnificent redwood may prove to be a host, although it's unlikely SOD will kill it outright. Likewise, foresters in Oregon may know if SOD has spread beyond a 9-square-mile quarantine zone where last summer they cut and burned several blocks of infested trees and shrubs. And researchers will probably know whether the disease, confirmed on one bigleaf maple tree in the Sierras, is viable there, where it threatens a very different ecosystem than the mild and misty climes along the Pacific coast.

Laboratory tests indicate that eastern red and pin oaks, some blueberry varieties, and perhaps certain rhododendrons, viburnums, and other landscape plants are highly susceptible to sudden oak death. If SOD takes hold in the Sierras, it will serve as notice that we have an implacable and extremely aggressive pathogen on our hands.

Sudden oak death is caused by a new pathogen, Phytophthora ramorum, that's related to the infamous Irish potato blight. No one knows where it caine from, although a similar strain of SOD recently showed up in Germany and the Netherlands and affects rhododendron nursery stock--but so far, no oaks or other trees.