Forest & Grassland Health

Spruce Needle Rusts

Aerial and close-up views of spruce needle rust in 2019.

Chrysomyxa ledicola Lagerh.
Chrysomyxa weirii H.S. Jacks.

Host(s) in Alaska:

Sitka spruce (Picea sitchensis)
white spruce (P. glauca)
black spruce (P. mariana)
Labrador tea (Ledum groenlandicum); alternate host

Habitat(s): current-year spruce needles, Labrador tea leaves; (spruce is the only host of C. weirii)
 

Photos

Click on the image for a larger version. All show Chrysomyxa ledicola.

Spruce needle rust sporulating on Sitka spruce in late-July.

Spruce needle rust sporulating on Sitka spruce needles on Wrangell Island in late-July.

Sitka spruce with orange-tinged new growth from spruce needle rust.

Sitka spruce with orange-tinged current-year needles caused by spruce needle rust.

Spruce needle rust sporulating on Labrador tea in June.

Spruce needle rust sporulating on Labrador tea in June.

Spruce needle rust spores on the water in Lake Clark National Park (credit: Jeff Shearer).

Spruce needle rust spores covering the water in Lake Clark National Park (Credit: Jeff Shearer, NPS).

Electron micrograph of Chrysomyxa ledicola spore (Credit: Steve Norton, NOAA).

Electron micrograph of a Chrysomyxa ledicola spore collected from Kivalina Lagoon in 2011 (Credit: Steve Morton, NOAA).

 

Current Status & Distribution in Alaska (2020 Update)

Spruce needle rust (Chrysomyxa ledicola) has historically been observed throughout much of Alaska’s spruce forests (Detection Maps). A major outbreak was aerially mapped across 116,000 acres in Western Alaska in 2019. The disease was also prevalent in 2020 but was not quantified by aerial survey. Ground surveys identified about 600 acres of damage near the junction of the Parks and Denali Highways. In addition, 86 ground observations came from FHP staff, while citizen scientists uploaded 15 research grade observations of the disease in iNaturalist. There was especially impressive damage along the Denali Highway and in Southeast Alaska near muskegs with the alternate host (Labrador tea). This disease rarely results in tree mortality, but trees can have whole needle cohorts missing where disease has been severe. Moderate to high levels of disease have been noted annually since 2017.

Chrysomyxa weirii is another, less common and less damaging, spruce needle rust in Alaska that is occasionally observed on 1-year-old needles in spring. It has been documented in coastal forests from the Kenai Peninsula to Prince of Wales Island. The maps below show georeferenced observations of both diseases.

Historic Activity

There has been a history of large spruce needle rust outbreaks in Alaska. In 2012, large outbreaks were reported in Lake Clark National Park, Katmai National Park, and the Kenai Peninsula, and notable needle rust also occurred in Southeast Alaska. In 2011, large quantities of rust spores washed ashore near the village of Kivalina in northwestern Alaska. This was somewhat mysterious since spruce is locally uncommon but found upriver, and no ground-checks of spruce could be made at the time. Significant spruce needle rust outbreaks also occurred in 2007 (Southeast Alaska) and 2008 (Interior Alaska). Click here for a summary of historic spruce needle activity and outbreak information from annual Forest Health Conditions in Alaska reports from 1969-2001.

Symptoms, Biology & Impacts

Heavily infected spruce trees have a distinctive orange tinge when the rust is fruiting on the needles in summer. However, sometimes trees are not obviously infected despite abundant orange spores on lake surfaces. Outbreaks are triggered by cool, wet weather in May, when fungal spores from Labrador tea (the alternate host) infect newly emerging spruce needles. Trees damaged by spruce needle rust are seldom killed, since damage is restricted to current-year needles, and the conditions for severe infection usually do not occur in the same location in consecutive years. Infected trees may be stressed or experience growth loss, but these impacts have not been quantified. 

The lifecycle of spruce needle rust.

The lifecycle of spruce needle rust (Chrysomyxa ledicola). Diagram by Paul Hennon.

Survey Method

Spruce needle rust disease information is largely qualitative and comes from ground observations made by Forest Health Protection staff, as well as land managers and the general public (disease signs and symptoms are easily identified). Occassionally, when disease severity is exceptional, the disease can be mapped by aerial survey.

Distribution Maps

Click map images for larger versions.

Spruce needle rust observations in Alaska as of 2020.

Detection locations of Chysomyxa ledicola and C. weirii in Alaska as of 2020 based on plot data, informal observations, and aerial detection survey. The distribution of spruce (Picea spp.) hosts in Alaska is shown. Modeled host tree layers were developed by the Forest Health Technology Enterprise Team in 2011 (240m-resolution, presence based on dominant tree species by tree diameter). 

Spruce needle rust observations in 2019.

Observations of spruce needle rust (Chrysomyxa ledicola) from aerial and ground surveys in 2019.

Links to Resource & Publications

Hennon, P. E. 2001. Spruce Needle Rust. USDA Forest Service Leaflet R10-TP-99. USDA Forest Service Region 10. Available here

 

Content prepared by Robin Mulvey, Forest Health Protection, robin.mulvey@usda.gov.

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