Trail Center logo

Theme: Parks with a Past

A Brief History of Bay Area Parks and Open Space
   Pt. 1, 1840s-1950s

A Conservation Timeline
   Pt. 1, 1840s-1950s

Up and Down the Peninsula and South Bay

Names on the Land
   Pt. 1, San Mateo County

Other Features

Sudden Oak Death

Oak Mortality Syndrome

Grazing Through Huckleberry Heaven

Old-Fashioned Huckleberry Muffins

Wild Lit

Note from the Literary Editor

Blacksmith Fork and Fox - Megan E. Hansen

Down Harkins Fire Road (El Mar de la Purissima - Greg Dunn


From the Editor

Park News

Trail Center Notes

Upcoming Events

The Trail Companion

Fall 2000

Oak Mortality Syndrome
A report from the Santa Cruz Mountains Bioregional Council meeting, Sept. 28, 2000

by Jeffrey A. Caldwell

Dear friends,
      That is the new name for what has been called "sudden oak death".
      Today I went to the meetings of the Santa Cruz Mountains Bioregional Council, which included a panel presentation and discussion: "Sudden Oak Death -- Dealing With a Potentially Devastating Forest Disease, and Lessons Learned from Pine Pitch Canker". The panelists were David Rizzo, the plant pathologist who recently identified the water mold causing the disease, Steve Tjosvold who conducts local field research on it, and Rick Hawley who studied the effectiveness of control methods for the unrelated Pine Pitch Canker disease.
      There are about 60 known species of Pytophthora, and the one causing the disease had not previously been described. As recent news stories tell us, it seems to be related to Phytophthora lateralis, which has caused losses of many Port Orford Cedars in recent decades. The common name for Phytophthora is "water mold" and it is related to the brown algae, but basically acts like what is commonly known as fungus, so everybody calls it a fungus. It is believed to be either exotic [possibly from the Orient] or a new hybrid. Exactly how it spreads is not known, though the organism has a waterborne stage, and mud is a major suspect. It seems somewhat like other species in the Pytophthora genus that may be vectored by blowing in the wind in a dormant stage. If that proves to be so, it is very bad news, impossible to contain it.
      It seems to grow best at temperatures of about 50 to 60 degrees, hardly at all over 80 to 90 degrees.
      It took so long to figure it out because usual methods of taking samples and submitting them for analysis were too slow, and the organism died before an attempt was made to culture it. Dr. Rizzo figured out what it was when he went out, collected a fresh sample and immediately drove back to his lab to culture it. The ususal method of taking a sample, keeping it a day, putting it in the mail, etc. resulted in the organism responsible for the disease dying before the culture was attempted.
      It is not believed to be spread by the beetles; they come after the disease develops. The mystery is that it attacks always above ground, low on the trunk of the tree. Can't figure out how it gets there. One theory is animals rubbing the bark. It was noted, if so, feral pigs are really bad news!
      Worst case scenario is that it could spread to all the black and red oaks thoughout North America.
      Best case scenario is that some freak event infected all the trees now dying several years ago. The "sudden death" is noted when the foliage begins to turn color. But I saw coast live oaks in China Camp State Park that were cracked with the black domes of Hypoxlyon thouarsianum fungus [one of the secondary attackers typical of the syndrome, which involves a number of native diseases and pests going after the weakened trees] well up their trunks which still had green foliage. It may be that the coast live oaks can hold off the Phytophthora longer than the tanbark oaks; that has proven to be the case in greenhouse studies where young trees were deliberately infected.
      The Port Orford Cedars are being protected in part by preventing access to them in the rainy season, particularly keeping vehicles on dirt roads from getting near them, which seems to be preventing new infections, though it is difficult to get cooperation from the public; some people crash through the barriers.
      It is now believed that any infected wood should be allowed to dry out and shouldn't be moved any further than necessary. The previous recommendation to tarp it with clear plastic is considered possibly a bad idea that would favor the disease more than hurt it. A new term that came up is "waste shed" -- infected wood probably shouldn't be allowed to leave a watershed. The infection is almost entirely in the bark and cambium, and only in the aboveground parts. It may sometimes enter the wood just a little, never more than an inch.
      The discussion was largely about what we don't know. The causitive organism was only discovered in June, and never seen before. The disease is basically only really active in cool, wet weather, so we will begin to learn much more as we get into the rainy season.
What we don't know:

  • Is is native or exotic? [though it certainly seems to be exotic]
  • How is it dispersed? How far?
  • Does it survive in soil or litter?
  • Does the pathogen survive in dead wood?
  • Does the pathogen survive in chipped wood?
  • How long does it actually take to kill a tree?
  • How does it interact with other diseases and pests to kill a tree?
  • Will fungicides control the pathogen?
  • What will the ultimate mortality be and what species will it spread to?

1 of 2 Next ==>