Forest & Grassland Health

Invasive Pathogens

Current Status (updated December 2017)

Fruiting bodies of Gemmamyces piceae on white spruce near Anchorage, AK.

Fruiting bodies of Gemmamyces piceae on white spruce near Anchorage, AK.

No serious exotic tree pathogens of native tree hosts have been confirmed in Alaska. Forest Health Protection is currently gathering information about a newly detected disease of spruce trees in Alaska, spruce bud blight (Gemmamyces piceae), for which the native/non-native status is unknown.

Spruce bud blight, caused by the fungus Gemmamyces piceae, was first detected on the Kenai Peninsula in 2013 and conclusively identified in 2016. Concerted monitoring in 2016 and 2017 found it to be widespread and common in Southcentral and Interior Alaska (over 100 detection locations), though not causing tree mortality and with the oldest infections dating back as far as two decades. Gemmamcyes has not been detected in Southeast Alaska. In 2017, spruce bud blight caused by two other fungi (Dichomera gemmicola and Camarosporium sp.) with identical signs and symptoms to Gemmamyces piceae were detected in coastal and coastal-boreal transition forests in Alaska.

Dichomera gemmicola is known to affect spruce and Douglas-fir in neighboring British Columbia and presumed to be native. Camarosporium is also thought to be native and appears to be a weak pathogen or saprophyte. A population genetics study of Gemmamyces piceae is being conducted in partnership with Drs. Gerry Adams and Sydney Everhardt at the University of Nebraska to better understand its native/non-native status. High genetic diversity of Gemmamyces piceae would indicate that this fungal pathogen has long been present, while limited diversity could support its more recent introduction. Spruce bud blight collections are being made throughout the state to better understand the distribution of causal fungi in Alaska.

Concern about Gemmamyces piceae was initially stoked by a recent publication (Cerny et al. 2016) describing outbreaks of spruce bud blight in blue spruce (Picea pungens) plantations in the Czech Republic that have resulted in significant tree mortality and plantation failure. The authors propose that the pathogen is not native to North America and could be devastating to North American spruce species if introduced, while another paper published in 2017 (Jaklitsch and Voglmayr) proposes that it is widespread in North America based on apparently scanty evidence. Mycological records in eastern Canada show that this fungus has been detected in North America before in New Brunswick and Nova Scotia ca.1990. 


Alaska is not safe from invasive pathogen introductions, particularly with increased trade and transportation and changing climate. Continued importation of live plant material and firewood are major potential pathways for invasive pathogen (and insect) introductions. Factors that may have protected Alaska from pathogen introductions in the past actually heighten our vulnerability. For example, low tree species diversity translates to potentially substantial, statewide impacts if introduced pathogens cause damage or mortality of our few dominant tree species; so far, the most devastating invasive forest diseases in North America have not affected our native trees. There can be lengthy delays between introduction and detection on our vast landscape, potentially allowing pathogens lag time to spread long distances via microscopic spores. Worldwide, there are no examples of the successful eradication of invasive plant pathogens established in forest ecosystems. Preventing invasive pathogens from entering Alaska must be the top priority.

Plant pathogens that are inconspicuous and minor in their native range can have major impacts in new habitats due to differences in host susceptibility and climate, which impedes our ability to anticipate new introductions. That said, Forest Health Protection and cooperators in Alaska have been working to identify potential invasive tree pathogens in Alaska, primarily based on host genus susceptibility (see Table). A thorough assessment of potential exotic tree pathogens requires a comprehensive list of native species for context. As tree pathogens are found and identified, they are compared to known native species to determine whether they are native or suspected of being introduced. Unfortunately, mycology and pathology in Alaska is not advanced to the point where such lists include all or most organisms. Field surveys and identification of tree pathogens should be a continuing, long-term goal of the forest health program. Importation of plants closely related to our native species is the most likely mode of invasive pathogen introduction.

Links to Resources and Publications

Ashiglar, S. M.; Hanna, J. W.; Ross-Davis, A. L.; Klopfenstein, N. B. 2014. The USDA Forest Service-RMRS forest fungi collection: Resource for fungal identification, developing biological controls, predicting invasive pathogens, and predicting potential impacts of climate change. In: Chadwick, K.; Palacios, P., comps. Proceedings of the 61st Annual Western International Forest Disease Work Conference; October 6-11, 2013; Waterton Lakes National Park; AB, Canada. Washington, DC: U.S.D.A Forest Service, Forest Health Protection. p. 127-130. Available here.

Černý, K., Pešková, V., Soukup, F., Havrdová, L., Strnadová, V., Zahradník, D., & Hrabetová, M. 2016. Gemmamyces bud blight of Picea pungens: A sudden disease outbreak in central Europe. Plant Pathology, 65(8): 1267-1278. Available here.

Jaklitsch, W. M. and H. Voglmayr. 2017. Three former taxa of Cucurbitaria and considerations on Petrakia in the Melanommataceae. Sydowia, 69: 81-95.

Klopfenstein, N. B.; Juzwik, J.; Ostry, M. E.; Kim, M.; Zambino, P. J.; Venette, R. C.; Richardson, B. A.; Lundquist, J. E.; Lodge, D. J.; Glaeser, J. A.; Frankel, S. J.; Otrosina, W. J.; Spaine, P.; Geils, B. W. 2010. Invasive forest pathogens: Summary of issues, critical needs, and future goals for Forest Service Research and Development. In: Dix, M. E.; Britton, K., editors. A dynamic invasive species research vision: Opportunities and priorities 2009-29. Gen. Tech. Rep. WO-79/83. Washington, DC: U.S. Department of Agriculture, Forest Service, Research and Development: 23-33. Available here


Content prepared by Forest Pathologists Robin Mulvey and Loretta Winton, Forest Health Protection, and

Return to Damage Agent Info/Homepage
Return to top