Spruce Bud Rust

Chrysomyxa woroninii Tranzschel 

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

Current Status & Distribution in Alaska (2023 Update)

In 2023, there were only five ground detection survey observations of spruce bud rust in Alaska on white and black spruce north of the Alaska Range near Healy and Donnelly, with two additional observations contributed via iNaturalist near Anchorage and Denali Park in Southcentral Alaska. Spruce bud rust has been recorded on white, black, Lutz, and Sitka spruce throughout Southcentral and the Interior (Detection Map) but does not usually occur on more than five trees per detection site. Similar to spruce needle rust, this fungus alternates on Labrador tea. 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 (Rhododendron spp, formerly in the genus Ledum).

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 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. 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

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, robin.mulvey@usda.gov.

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