Spruce Bud Rust

Spruce bud rust was recorded more than usual in Southcentral Alaska this year.

2024 Ground Detection Survey Observations: 13 total observations on white spruce, 8 in the Interior and 5 in Southcentral in Anchorage and on the Kenai Peninsula. 

2024 iNaturalist Observations: 30 in Southcentral and Interior Alaska, with the greatest concentrations near Anchorage, the Kenai Peninsula, and Lake Clark National Park. 

Spruce bud rust has been recorded on white, black, Lutz, and Sitka spruce throughout Southcentral and Interior Alaska (Detection Map), but the disease does not usually occur on more than five trees per detection site. The disease results in stunted shoot formation due to infection of buds and female cones. Similar to spruce needle rust (Chrysomyxa ledicola), this fungus also has life cycle stages on Labrador tea (Rhododendron spp, formerly in the genus Ledum).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.

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 United Kingdom, 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.

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

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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.