Forest & Grassland Health

Spruce Bud Rust

Chrysomyxa woroninii Tranz.

Host(s) in Alaska:

Black spruce (Picea mariana)
Lutz spruce (P. sitchensis x P. glauca)
Sitka spruce (P. sitchensis)
white spruce (P. glauca)

Habitat(s): buds and female cones (Labrador tea is alternate hosts)


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Spruce bud rust, Chrysomyxa woroninii.

Spruce bud rust on white spruce west of Glenallen.

Spruce bud rust, Chrysomyxa woroninii.

Aecia of Chrysomyxa wornoninii.

Spruce bud rust, Chrysomyxa woroninii.

Spruce bud rust on white spruce.

Spruce bud rust, Chrysomyxa woroninii.

Spruce bud rust near Mount Ryan, Steese Highway.

Spruce bud rust, Chrysomyxa woroninii.

Old spruce bud rust infections along Taylor Highway near Tok.

Current Status & Distribution in Alaska (2020 Update)

There were seven observations of spruce bud rust in 2020, six of which came from FHP staff and one from a citizen scientist on iNaturalist. All observations occurred within a similar footprint to those made since 2018, when the disease was noticed and incorporated into exploratory ground surveys. Since the first report in Alaska on white spruce near Fairbanks in 1979, spruce bud rust has been recorded on white, black, Lutz, and Sitka spruce throughout Southcentral and Interior Alaska (Detection Map). We have found it as far north as Coldfoot in the southern Brooks Range, as far southwest as Katmai National Park, and east to the Tetlin National Wildlife Refuge near the Canadian Border. The disease results in stunted shoot formation due to infection of buds and female cones. The disease also has life cycle stages on Labrador tea (Ledum spp.).

Historic Activity

Spruce bud rust is a circumboreal disease of white and black spruce buds and female cones that results in stunted shoot formation. The disease is infrequently observed and does not cause severe damage to spruce. It was first described in 1824, and Labrador tea (Ledum spp.) was confirmed as the alternate host in the 1950s. In the UK, perennial broom symptoms on Labrador tea are more noticeable than on spruce. In Alaska, detection of the disease in 1979 on spruce regeneration at the Bonanza Creek Experimental Forest prompted study of the pathogen and symptom development in spruce (McBeath 1984). It has mostly been observed on white (and occasionally black) spruce in the Interior, but in 2018 it was also found on Sitka and Lutz spruce on the Kenai Peninsula. Our understanding of the distribution of this disease in Alaska is increasing each year as we document field observations.

Biology & Symptoms

Spruce bud rust results in stunted shoot formation when buds and female cones are infected. The disease also has life cycle stages on Labrador tea (Ledum spp.). Crane et al. 2000 published about the pathogen's lifecycle in detail. Spruce needle rust, Chrysomyxa ledicola, also cycles on spruce but C. ledicola infection and symptom onset occurs later in the season, and affects fully elongated needles rather than stunted shoots and cones.

Survey Method 

This disease is infrequently observed and is generally detected through informal ground observations.

Detection Map

Locations of Chrysomyxa worononii in Alaska as of 2020.

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

Resources & Publications

Crane, P.E., Hiratsuka, Y. and R.S. Currah. 2000. Clarification of the life-cycle of Chrysomyxa woroninii on Ledum and Picea. Mycol. Res. 104(5):581-586. Available here.

McBeath, J.H. 1984. Symptomology on spruce trees and spore characteristics of a bud rust pathogen. Phytopathology 74(4):456-461. Available here.


Content prepared by Robin Mulvey, Forest Health Protection,

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