Sudden Death Looms for Oaks.

A swift-moving disease threatens California's signature tree, among others--and raises the specter of Dutch elm disease and chestnut blight.

It's not an obsession; after all, Kent Julin gets paid for looking at trees. Still, each day when he comes home he can't help but examine the two young coast live oak trees in his yard. Sometimes he imagines the bark of the Quercus agrifolia suddenly flecked with oozing, dark-hued droplets, though a closer look finds nothing amiss. In a passing breeze he even imagines spores lighting on the trees, although spores, the reproductive essence of microorganisms, are way too small to see.

But as forester for Marin County, California, Julin is all too aware that his trees, healthy though they appear, are at almost certain risk of contracting a new and deadly disease: sudden oak death (SOD).

Marin County is ground zero for sudden oak death. The disease was first reported in 1995 on a clump of tanoaks (Lithocarpus densiflorus), relatives of both oaks and chestnuts. The effected trees were in a backyard in Mill Valley--the Bay Area burg was Julin's boyhood home. By '97 the disease had appeared on coast live oaks and California black oaks (Quercus kelloggii), but in such low numbers that few people paid attention.

That changed when the disease hit big time in the summer of '99. Now tens of thousands of dead and dying trees mark the backyards and byways that wind among Mann's lovely hills. Santa Cruz County is just as bad off, and the disease is moving with lethal speed through Monterey, Napa, Sonoma, San Mateo, and Santa Clara counties.

This poses both ecological and economic angst. Wherever trees die en masse, erosion, stormwater runoff, and the threat of wildfires follow; watersheds can become more drought-prone, landslides more likely, and wildlife habitat deteriorated. Homeowners' property values can drop, for just one coast live oak--California's signature tree--can add upward of $10,000 to the worth of a home. Plus those dying trees have to be removed at close to $1,000 a pop.

And there's no cure in sight.

Adding to Californians' fears (along with those of horticulturists, plant pathologists, and foresters around the world) was an announcement in January that a disease on rhododendron nursery stock in Santa Cruz County--and a disease on rhododendrons in Germany and The Netherlands--was none other than sudden oak death. Oaks may not be big-ticket items in the national and international nursery trade, but rhododendrons are. And global trade drives the rapidly increasing spread of every class of invasive organisms.

Could SOD spread to other species of oak in North America? Perhaps. A worst case scenario would be one or more of our beautiful oaks proving so susceptible that a plague comparable to Dutch elm disease or chestnut blight would sweep major ecosystems, even continent-wide.

And what about native rhododendrous; are they also in danger? It's simply too early to tell, says Susan Frankel, a Forest Service plant pathologist and head of the California Oak Mortality Task Force, "The California Native Plant Society has an amazing database; they know where many of California's two native species of rhododendrons are located. We'll be hiking out to look for signs of disease as the season progresses. Fortunately, while rhodies are highly susceptible to several different phytophthoras, it's rare they die from them."

Then in February researchers found SOD on native evergreen huckleherry, a rhododendron relative, in California's Muir Woods. The huckleberries died to the ground, which raises the specter of blueberries and cranberries succumbing as well. The huckleberry is native throughout the Pacific Northwest, providing yet another avenue for spread of the disease.

Researchers likewise found SOD on Shreve's oak (Quercus parvula var. shrevei) a locally common denizen of coastal areas. By April, SOD had turned up on rhododendron relatives Pacific madrone (Arbutus menziesii) and hay laurel (Umbellularia californca), as well as viburnums in Germany, which raises concern not only for our native viburnums but for their relatives, honeysuckles and elderberries.

What causes sudden oak death? Though most reports call it a new and yet-unnamed fungal species in the genus Phytophthora (fy-tof-thor-a), it isn't--quite. Formerly classified as fungi, phytophthoras are adaptable and aggressive algae-like pathogens. (It was a phytophthora that precipitated the Irish potato famine in the mid-19th century.)

Nor are these pathogens new to California or its oaks. At least two related species attack oaks inadvertently overwatered by homeowners caring for their lawns, and the symptoms mimic SOD. Still, this phytoplithora could spread faster and further than most. Its spores are carried by soil and rain-splash and may be airborne as well.

Regardless how the tree becomes infected, the symptoms of sudden oak death are similar. Often the first sign is black or burgundy sap oozing from tiny holes in the bark; soon after, the tree wilts, turning starkly brown. Yet "sudden oak death" is a misnomer, says Frankel. "Trees are affected long before the symptoms show. By the time you see that oozing sap, your tree is almost dead. The pathogen has already attacked the bark, killing the tissue that carries sugars from the leaves to the roots and essentially girdling the tree."

Then come ambrosia beetles and western oak bark beetles by the thousands, flocking to feed, tunnel out galleries, and lay their eggs. (Most phytophthoras produce a tart, winelike odor that attracts insects.) Between the beetles and the secondary pathogens they carry, the tree is finished.

Losing the oaks will distress more than property owners. California's oaks provide a substantial and reliable source of food to legions of animals both large and small, from the threatened northern spotted owl to the dusky-footed woodrat it hunts. After species such as oak die, they can provide homes for creatuers for a century or longer--but not if the trees die of sudden oak death. Riddled by beetles and weakened by secondary infections, the trees begin to break apart within a year or two.

Firefighters are especially concerned about the far-reaching effects of SOD because they rely on mixed oak woodlands to slow and cool fires during dry months when California's hillsides burn. Few "ladder fuels," the underbrush that carries flames into the canopy, grow under oaks. But once the oaks die, grasses and exotics, like Scotch broom, will seed in aggressively, provoking a hotter flame.

With the oaks dead and dry as tinder, and their dropped branches cluttering up the understory--acting as ladders into the canopy--the tables have turned. Fires that would have crept through the understory will roar through their crowns, What's worse, trees that are still green may have also succumbed to sudden oak death. Julin, the forester, has found some that contain 20 to 40 percent less water than healthy oaks--bad news for the tens of thousands of homes nestled among woodlands at the ends of narrow, brush-encumbered driveways.

Will SOD attack other species of oaks and spread to other regions? Where exactly did SOD come from and can we hope for a cure? "People are asking questions and they want to do something right now, and we can't tell them what to do," says Terry Shaw, national program leader for the Forest Service's Pathology Research.

But not all the trees in affected areas have succumbed, so there's hope. One of Shaw's priorities is determining how heredity or habitat, or the complex interplay of both, may influence a tree's apparent resistance. A second goal is understanding dispersal. A combination of inherent and environmental factors may be involed; cool temperatures and moisture-laden air seem conducive to SOD's spread.

"There are habitat conditions in eastern North America that get hells ringing in your head," says Shaw. "While disease spores may not make it that distance on their own, they might through shipments of rhododendrons or via vacationers who inadvertently carry diseased material to new settings. So we're testing an array of oaks from across the country and around the world to see if others could be vulnerable."

Because this is a bark disease, researchers are not only looking at seedling susceptibility but using a new technique that keeps cut branches "alive" long enough to see if SOD will take hold under its favorite conditions. They're also checking related species--chestnuts, beeches, and chinquapins--as well as rhododendron and huckleberry relatives: manzanitas, cranberries, and more.

The California Department of Food and Agriculture in May quarantined the sale of and materials from all known host plants and trees. California and the Forest Service are plowing $10 million and $3 million, respectively, into research.

It may seem odd that no one quite knows where SOD came from. But millions of constantly evolving microorganisms inhabit almost every square meter of earth. It's likely that fewer than 10 percent have been identified, even among the ones in our own backyards. Most microorganisms are willing hybridizers and mutators, easily adapting to changing circumstances. As for a cure, no ones feeling too sanguine. While people can spray or inject yard trees with fungicides (an expensive proposition on something the size of an oak) to slow the disease, aerial spraying of woodlands full of homes isn't such a good option.

"People think that science will solve this with a spray or an injection," says Julin. "But it's not going to happen that way. The tanoaks are so susceptible, we could even lose them all. Some live oaks and black oaks may have resistance, though it's too early in the game to know anything for sure. Regardless, the only cure is natural selection: the survival of those that can."

Mary Woodsen writes about natural history and environmental issues from Willseyville, New York.

WHAT TO LOOK FOR, WHAT TO DO

Maintain the health of your trees; that's the best defense.

* California's oaks are adapted to the dry climate and rarely require watering except under severe drought. Watering lawns around oaks can weaken the trees and promote disease.

* Root zones are vulnerable. Make the root zone--the diameter of the crown, plus a third--a zone of no disturbance: Don't pave or compact the soil.

* Protect the trunk and lower limbs from injury.

* Prune branches during dry summer months, when the Phytophthora and insects are least active.

* Fertilize for yellowed leaves or other signs of deficiency if confirmed by a laboratory test.

* Monitor your trees year round for bleeding symptom, then confirm that the new Phytophthora species is the cause. Many things can cause trees to bleed--from mechanical damage (caused by ladders and kids) to other diseases and insects, such as carpenter worm and sycamore borer.

* Both. University of California Berkeley and the California Oaks Foundation are testing products that might be used to protect trees from SOD.

No cure is known for trees with Sudden Oak Death. Still, you may be able to extend the life of a tree--though no method is certain. Options include:

* Using fungicides for other Phytophthora-caused diseases;

* Applying insecticides that target adults before flights and colonization in spring and fall. Timing can vary from year to year, so call a cooperative Extension agent to find out when beetles are on the move.

Consulting an arborist for advice on spraying.

* Checking out the website of the California Oak Mortality Task Force (www.suddenoakdeath.org).

Large accumulations of beetle boring dust around the base of the trunk or branches mean your tree is dying and cannot be saved. Confirm this diagnosis with a certified arborist and consult about removing the tree.

* Do not take action until a diagnosis has been made.

* Avoid cutting dead oaks from mid-October to the end of April Of course, dead trees that represent a hazard should be removed immediately.

* Split the wood and chip the branches, leaving them on the property.

* Promote drying of wood where possible by stacking in a sunny location.

* Avoid grinding the stump, to reduce equipment contamination.

* Cover the stump tightly with clear plastic; this may help kill the fungus and reduce insect emergence.

* Avoid transporting infested or potentially infected logs, branches, or firewood--to help slow the advance of SOD. This pathogen may also he spread by shoes, by contaminated equipment (saws, shovels, vehicles, etc.), by soil, and in surface and ground water. Clean your equipment and shoes with Lysol or a 10 percent bleach solution before leaving the infected area.

--Mary M. Woodsen