Fungus imperils Port-Orford cedar. (Clippings).

If you're hiking or hiking in Oregon's Siskiyou National Forest or California's Klamath National Forest during the rainy season, you'll need to hose down those muddy boots and tires as you move from site to site-you may even have to avoid some trails completely.

The precautions, set up by the Forest Service and the Bureau of Land Management, are intended to prevent the further spread of a fungal disease that's been killing Port-Orford-cedar (Chamaecyparis lawsoniana). The fungus, Phytophthora lateralis, is carried by water. Its spores attach to the tree's roots, causing the smallest ones to disintegrate, then moves part way up the trunk. As the disease creeps up, the crown dies and bark beetles move in to speed the tree's demise.

"It happens very quickly, as though the tree had been strangled," says Alan Hoffmeister, a spokesman for the BLM's Coos Bay (Oregon) District Office.

The root disease has been around for a long time, but in recent years the disease seems to be spreading, so the agencies have stepped up their efforts to contain it. According to the Forest Service, the disease was first discovered in 1923 on ornamental Chamaecyparis lawsoniana growing in Seattle. Nearly 20 years later, it was found in Oregon's Willamette Valley and named. By the mid 50s it had spread to southern Oregon. A Forest Service report says, "Aerial photographs taken in 1956 showed a network of dying trees along watercourses, around lakes and sloughs, and along rural roads, livestock trails, and farmsteads."

Between that time and the 1980s logging was also expanding. "So in retrospect, we can say 'Yes, the expansion of logging in that area spread the disease,' " says Jeff Davis, silviculturist for the Coos Bay District and its Port-Orford Cedar coordinator. That's why the Forest Service and Bureau of Land Management have stepped up precautions during the rainy season, closing roads and hosing down vehicles that have been in areas that might he affected. One gallon of bleach for every thousand gallons of water has proven effective for killing the fungus and has been approved as a pesticide, Davis says. And both agencies are working to create disease-resistant varieties of the Port-Orfords.

Meanwhile, Davis says, the disease "is not wiping out Port-Orford. You can drive right to where they first found the disease and find diseased trees right next to live ones." And unlike other conifers, Port-Orford cedars produce seeds at a young age. So the "biggest long-term threat is that you may not see Port-Orford cedar as an old-growth species in the future," but you'll still see the tree.