Diplodia Gall

Diplodia tumefaciens (Shear) Zalasky

Host(s) in Alaska:

trembling aspen (Populus tremuloides)
balsam poplar (P. balsamifera​)
other Populus spp.

Habitat(s): tree boles and branches

General Distribution in Alaska: Southcentral and Interior Alaska

Current Status & Distribution in Alaska (2024 Update)

Only a few new observations of this disease were made in Alaska this year. We have documented this disease 45 times total, 44 times on trembling aspen and once on balsam poplar.

2024 Ground Detection Survey Observations: 1 observation on balsam poplar near Anchorage. 

2024 iNaturalist Observations: 1 observation on balsam poplar near Eagle River. 

Distribution, Symptoms & Impacts

This disease is well distributed throughout the surveyed range of aspen in Alaska. Galls caused by the fungus can weaken stems and branches, but generally do not kill trees. Here, the disease is most often found on aspen, but can also occur on balsam poplar and other Populus species. Affected trees occur in small, discrete patches, less than two acres in size. When occurring on the trunk rather than branches, it strongly resembles Chaga/cinder conk (Inonotus obliquus); however, the cinder conk occurs on birch. Similar looking galls on small branches have been attributed to the poplar budgall mite (Aceria parapopuli) in British Columbia, Canada. More work is needed to determine if multiple organisms contribute to stem gall development on aspen in Alaska, and whether they can be reliably distinguished in the field. 

Survey Method 

This disease is surveyed through ground detection surveys and information observations, as well as boreal forest monitoring plots.

Detection Map

Links and Resources

More images of diplodia gall available at the IPM Images website

Content prepared by Robin Mulvey, robin.mulvey@usda.gov and Lori Winton, loretta.winton@usda.gov, Forest Pathologists, Forest Health Protection 

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