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August 15, 2017
Vol. 4, Issue 4
August 2017
Save the Date!     

August 24-25 - 2017 California SAF Summer Meeting - Value Added Forestry; Gaia Hotel and Spa, Anderson, CA

September 18-21 - National Association of State Foresters Annual Meeting; Charleston, WV

September 19-21
- 2017 Southwestern Tribal Climate Change Summit; University of San Diego, San Diego, CA

October 17-19 - The Riparian Summit: Confluence to Influence; UC Davis, Davis, CA

November 15 - 16 - 2017 California Forest Pest Council Annual Meeting; UC Davis Student Community Center, Davis, CA  

August 5-10, 2018 -  The 6th International Conference on the Genetics of Tree-Parasite Interactions: Tree Resistance to Insects and Diseases: Putting Promise into Practice; Mt. Sterling, OH  
An Invisible Variable in Tree Mortality
A lot of attention has been devoted to California's extended drought, with more than a hundred million Sierra Nevada trees succumbing to lack of water and native bark beetles. Yet, in many cases, root diseases may also have played a role in tree
Douglas-firs affected by root diseases and several beetle species. Photo by C. Lee, Cal Fire. 
weakening and mortality. While the drought and bark beetle attacks are episodic, once root diseases are present, they are chronic and long-term. Determining when root diseases are present can help to ward off further stand decline through preventative management activities.
Pathogens infect tree roots in many ways (e.g., through healthy tree roots in contact with infected ones, pathogen-transmitting insects, or spores infecting wounds at the base of a tree), but a tree that is otherwise healthy can keep infection at bay for decades. However, when stresses such as severe drought impair a tree's ability to produce chemical and structural defenses, root pathogens can colonize large parts of the root system, causing further tree stress. Bark beetles often then move in to the weakened tree and begin to build up populations that, when large enough, can overcome stands of healthy trees.
The most damaging and widespread root disease of conifers in California is Heterobasidion, a fungal genus found throughout
Fruiting bodies of Heterobasidion occidentale. Photo by C. Lee, Cal Fire. 
most of the state's 8 million acres of conifer forests. Depending on the species of tree and fungus, infection can result in basal decay, increased attractiveness to bark beetles, or outright tree death. If left undisturbed, Heterobasidion can travel 8 - 80 in per year; disturbances can have varying impacts on spread depending upon the activity. For instance, cutting green trees increases forest disease centers as the fungus produces spores that infect the tops of green stumps. Wounding of trees can also promote infection of some species. Fortunately, since Heterobasidion infects trees primarily as a result of management activities, techniques are available to greatly reduce post-harvest infection. Techniques may also be available to make stands more resistant to other root pathogens. For more information about root diseases, contact your local University of California Cooperative Extension Advisor, Cal Fire Forest Pest Specialist, or US Forest Service Plant Pathologist.
New Invasive Shot Hole Borer Resources 
The following resources for California's invasive Kuroshio and polyphagous shot hole borers are now available online.

An Invasive Shot Hole Borer and Fusarium Dieback Field Guide offers background information on the beetle/disease complex as well as on beetle biology, signs and symptoms, look alikes, and host species impacts.   

An Invasive Shot Hole Borers + Fusarium Dieback Sycamore Assessment
guide was developed by the Eskalen UC Riverside lab with support from the Los Angeles Center for Urban Natural Resources and Sustainability to improve monitoring consistency when assessing sycamore trees for shot hole borer injury. 
Newsletter feedback and ideas are welcome.  Please submit comments to

When buying firewood for camping this summer, remember to buy wood sourced local to where you will be using it, helping to minimize the spread of pests and diseases - Buy It Where You Burn It.  For a list of local firewood dealers, go to


Katie Harrell
Communications Director  
California Forest Pest Council
California Forest Pest Council | (510) 847-5482 | |

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