Where Have All the Oak Trees Gone?

Sudden oak death affects tanoaks, coast live oaks, and black oaks. It first appeared in Marin County, California in 1995 on a tanoak. Since then it has spread as far north as Humboldt County and as far south as Monterey. Three counties have epidemic levels of oak mortality -- Marin, Santa Cruz and Monterey. The spread of the disease is so epidemic in Marin County that a state of emergency was declared in 2000. The county received $3 million from the state to help them fight the epidemic, which includes not only the dead trees but the threat of wildfires caused by the increasing amount of deadwood.

The widespread death of the trees poses some environmental concerns. Among these are worsened wildfire conditions from dead trees, the death of animal species that depend on the oaks for food, and the loss of earth stability when the tree roots die.

The University of California is researching Sudden Oak Death, and has isolated two fungi that are rare (new) forms of a fungus called Phytophthora. A variety of this fungus is what caused the Irish Potato famine -- the ones killing oak trees are Q. agrifolia and Q. kelloggii. The earliest detectable symptom of SOD is 'bleeding' and oozing of reddish to brown viscous material from patches on the trunk, and beetle boreholes with conical piles of frass, reddish-brown-light, nearly white. The weakened bark on the affected tree makes it easier for the beetles to penetrate the bark.

Spotting the symptoms of SOD is difficult in the early stages. First there are wilted shoots, then older leaves become pale green. Within a couple of weeks the foliage turns brown, whatever the time of year, but clings to branches. The lower trunk will exude a dark brown sap that stains the bark surface...by this time the tree is dying.

The U. of Cal at Berkeley has set up a program to study five sites in Marin County. The sites contain Tanoak, Coast Live Oak, Black Oak and Valley Oak. At these sites, 20 plots have been established to monitor the oaks. Each plot as 30-50 trees. The study began in March of 2000, and the second round of data was completed in June of that year. Since then the entire study has been compiled. Thirty to forty percent of the trees studied had symptoms of SOD. During 2000 and the first half of 2001, the trees were studied at 6 week intervals..

The public can participate in the project, which has become ongoing, and view the results. A website has been developed where hikers and others who notice symptoms on trees can enter their information online. Information is available about spotting symptoms of disease and how to identify the different kinds of trees and enter your information as a point on a map.

In August of 2000, the California Oak Mortality Task Force was formed as part of the California Forest Pest Council. The Task Force organizes public agencies, other non-profit organizations and private interests to address the issue of elevated levels of oak mortality. They have some called OakMapper, so people in California can search for infestations by zipcode, congressional district or county. Their website is: www.cnr.berkeley.edu/comtf/.

If the infestation of trees is caught in the early stages, a pesticide can be used to prevent beetles from getting into the bark. A pesticide called ASTRO has been successful and can be sprayed on trees to a height of 10 feet. Of trees treated with the pesticide in 1999, 12 out of 14 survived.

However, citizens are advised not to attempt using fungicides themselves to treat the trees. Most fungicides are difficult get into the tissues of the tree cankers, and commercially sold fungicides inhibit fungal growth but don't kill the fungus. Modern systemic fungicides are selective and only work on some fungi; to kill strains of Phytophthora a special fungicide is needed. Also, if improper or poorly prepared fungicides are used, they can lead to a buildup of resistance in the tree fungus; have negative effects on other organisms on and around the tree, including beneficial fungi; and can lead to direct injury of the affected tree.

If diseased trees are spotted, contact the U.S.D.A. Forest Service at: www.fs.fed.us/foresthealth or the University of California, Berkeley at http://camfer.cnr.berkeley.edu/oaks/.

Linda Richards of San Anselmo has come up with her own cure for the oak trees in her backyard. She applied Tea Tree Oil to the oozing cracks in her trees; she reports that her trees continued to thrive with a dark stain on the bark. She says,

"Tea Tree Oil is available at drugstores or at a health food store. It is marketed as an antiseptic, fungicide, germicide for human use. I injected a small amount of the oil into the oozing cracks of the bark with a large plastic syringe every 5 days or so for a few weeks, using a total of about 1.5 oz."

In 2001 the fungus was discovered on rhododendron plants adjacent to oak trees. It causes the same cankers and dying back of branches. It has been found not only in California, but in Germany and the Netherlands.

In March of 2001 the Canadian Food Inspection Agency implemented a policy to attempt to stop the transportation of plants from California that could contain the fungii that cause SOD. Canada has now restricted not only plants but soil, sawdust and other peripheral items from California.

According to Matteo Garbelotto, a plant pathologist and adjunct professor in the Department of Environmental Science, Policy and Management in U.C. Berkeley's College of Resources, "We now know we have a host that could have carried the fungus a long way. People don't really export oak trees across state lines or around the world, but they export rhododendrons."

It was a British researcher named Clive Brasier who first discovered the fungus on rhododendrons. He was in Berkeley during the summer of 2000, working with Garbelotto, and subsequently noticed the fungus after returning to Europe.

Some of the infected groves had an 80% mortality rate of trees, as of August, 2001, and research and treatment have done little in the past year to slow that rate.

Advice is now to not transport any wood products out of California including mulch, bark or firewood, or rhododendron plants. After visiting an infected area clean the soil from your shoes and remove any soil from vehicles, sport or construction equipment. The fungii can live in mud and soil.