Sooty Bark Disease


Cryptostroma corticale spores - M. Elliott, WSU
Photo Credit: Marianne Elliott, Washington State University

Cryptostroma corticale

Sooty bark disease is caused by the fungus Cryptostroma [Biscogniauxia] corticale.

The  ‘sooty’ fungal structures may be observed growing on the stem or branches where the bark has flaked off.

These fungal structures release tiny spores that can spread via the wind during certain times of the year (When? See research needs).

More Information

Please check our other webpage for more information and resources:

Sooty Bark Diseaese, Ornamental Plant Pathology Program, Washington State University

Is this Sooty Bark Disease?

You’re welcome to send samples to our lab for confirmation.  Instructions for collecting samples are available here.

Contact us if you’re interested in submitting a sample.

The Pacific Northwest Story


C. corticale found in Seattle, WA

Bartlett Tree Experts confirms the presence of C. corticale on 10 trees in Seattle in cooperation with Seattle Parks and Recreation.


C. corticale found in more Puget Sound cities

The Ornamental Plant Pathology program at Washington State University confirms the presence of C. corticale on a number of trees from cities of Tacoma, Bellingham, Anacortes, and Olympia.


iNaturalist project launched

The Sooty Bark Disease Watch project on iNaturalist is launched for a community effort to advance knowledge about the disease distribution and susceptible hosts.


In general, it is our understanding that C. corticale has been present and spreading in Washington (and greater Pacific Northwest) since at least the late 1960s, but it did not emerge as an noticeable issue until recently.

Why is this disease emerging now?

Longer and Hotter Summer Droughts

Sooty bark disease is likely emerging as an issue now because of the recent increase in the length and intensity of the summer droughts in the Pacific Northwest. 

These changes in climate are likely driving the emergence of sooty bark disease for two reasons:

Increased Tree Stress

Trees are more stressed because of the increased length between rain events

Favorable Fungal Growing Conditions

The fungus is favored by warmer temperatures, growing faster and 'behaving' more aggressively.

"The impacts of this disease on our forests and communities are likely to get worse as summer droughts become longer and hotter in the Pacific Northwest"
Joey Hulbert
Program Director

Learn More

Research Needs (Brainstorm)

Fungal Life History
  • General seasonality and conditions necessary for spore production and release (i.e. to inform decisions about when to prune nearby trees).
  • Conditions necessary for infection
  • Tree susceptibility after wounding or injury
  • Seasonal and climatic conditions when spore loads are highest
  • Investigating whether sporulation occurs on wood chips or mulch
  • Susceptibility of various tree tissues
Management & Control
  • Importance and efficacy of sanitizing tools, gear and equipment in between jobs
  • Efficacy of phosphonates tree injections or chemical controls
  • Biocontrol options
Public Health
  • Evaluation of risk in day to day activities of professionals
  • Precautions to reduce risk of inhaling spores

Public Health Concerns

Please note, inhaling spores from Cryptostroma corticale can cause hypersensitivity pneumonitis or temporary respiratory issues in some people. If you’re vulnerable, we recommend wearing a N95 mask or respirator for protection against inhaling the fungal spores while handling possibly infected plant samples. If you’re concerned, please read more at this Maple Bark Disease resource provided by the Washington State Department of Health. 


What are your research needs?

What questions do you have?

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    Get Involved

    Share observations on iNaturalist

    You can accelerate research about the breadth and impact of sooty bark disease. Join the iNaturalist project and share observations of trees infected with sooty bark disease. This information will help us understand where the disease is affecting trees and which species are susceptible.

    Upcoming Research

    Is the prevalence of Sooty Bark Disease worse in hotter areas of Tacoma?

    Together we can answer this question.


    Air temperature data collected in July 2018 and shared by the City of Tacoma. Learn more in the Tacoma Community Forestry Story Map.

    Visit our webpage here to accelerate research in Tacoma

    Contact Us