The Trees are Bleeding

by Bethany Kyre, BS Agriculture, Plant Pathology

Sudden oak death

Joseph OBrien, USDA Forest Service,

Have you ever seen a tree bleed? Not figuratively. Literally. Have you ever seen a tree exude a red viscous liquid in quantities enough to run down the trunk in long, sticky streaks? I have.

Enter Phytophthora ramorum, the fungus like pathogen responsible for Sudden Oak Death. The official origin of the pathogen is still up for debate, as are many aspects of its lifecycle, but the leading theory is that it arrived in the Bay Area of California on infected rhododendrons. The disease causes high instances of mortality in oaks, especially coast live oak, and tanoaks, trees which play a large role in the grassland ecosystems surrounding San Francisco.

Since its entry into the US in the 80’s, much work has been done to understand the spread and epidemiology of the disease. Forest pathologists from around thecountry, including researchers here at Ohio State Plant Pathology, have put their heads together in an effort to stop the spread of the disease, still, much remains unknown.

Hypoxylon canker

Thomas Smiley, Bartlett Tree Experts,

Here is what we DO know:

  • Sudden Oak Death is a rather complex system that involves a fungal-like organism (oomycete) ramorum, several species of bark and ambrosia beetles, and a decay fungus, Hypoxylon atropunctatum.
  • Bay laurel, a common tree often interspersed with coast live oaks, plays host to ramorum, where it causes little more than leaf blight.
  • Trees can enter remission once infected, though the mechanisms behind it have yet to be explained.
  • P. ramorum is an oomycete and requires two separate mating types to reproduce sexually – this has not been observed in a field setting.

It is important to be diligent when it comes to invasive diseases and pests, as prevention is the best method for controlling the spread of diseases and insects. Quarantines should be followed, hikers should stay on trails and check boots for caked on dirt, and clothing for plant matter or burs, and wood and other tree products should not be moved.

This blog post was an assignment for Societal Issues: Pesticides, Alternatives and the Environment (PLNTPTH 4597). The views expressed are those of the author and do not necessarily reflect the views of the class, Department of Plant Pathology or the instructor.


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