Forest & Grassland Health

Diplodia Gall

Diplodia tumefaciens (Shear) Zalasky

Host(s) in Alaska:

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

Habitat(s): tree boles and branches


Click on the image for a larger version.

Gerry Adams stands beneath a large Diplodia gall near Nenana.

An exceptionally large Diplodia gall on aspen.

Diplodia gall on trembling aspen.

Diplodia gall on trembling aspen.

Diplodia gall on trembling aspen.

Diplodia gall on trembling aspen.

Diplodia gall on trembling aspen.

Diplodia gall at the fork of trembling aspen.



Current Status & Distribution in Alaska (2020 Update)

Diplodia gall was recorded at nine sites in 2020. Over the past few years, we have documented its occurrence at 36 locations, well distributed in the Interior from north of Fairbanks to the Canadian border, and at fewer locations in Southcentral, including the northern Kenai Peninsula (see Map). This disease is reportedly distributed throughout North America on trembling aspen, balsam poplar, and other Populus species, but to date we have only recorded it on aspen in Alaska. The patches containing affected trees are generally small and discrete, less than 2 acres in size. When occurring on the trunk, it strongly resembles Chaga, also known as the cinder conk (Inonotus obliquus). However, Diplodia gall has only been found on aspen in Alaska, whereas the cinder conk is most common on birch. Galls caused by the fungus can weaken stems and branches, but generally do not kill trees.

Survey Method 

This disease is surveyed through informal ground observations and boreal forest monitoring plots.

Distribution in Alaska

Locations with Diplodia gall in Alaska as of 2020.

Georeferenced observations of Diplodia tumefaciens in Alaska as of 2020 with the modeled distribution of trembling aspen. Host tree distributions were developed by the Forest Health Technology Enterprise Team in 2011 (240-m resolution, based on dominant tree cover by diameter).

Links and Resources

More images of diplodia gall available at the IPM Images website


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

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