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

Current Status & Distribution in Alaska (2023 Update)

This year, Diplodia gall was recorded on trembling aspen at four locations along the Parks Highway in Interior Alaska and on a single trembling aspen near Anchorage. Two research grade iNaturalist observations on black cottonwood were made near Anchorage. This disease is well distributed throughout the surveyed range of aspen in Alaska (see Detection Map). 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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