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Extension > Garden > Yard and Garden > Spruce needle rust

Spruce needle rust

Michelle Grabowski - University of Minnesota Extension Educator
Cynthia Ash Kanner - former University of Minnesota Extension Specialist

Back to Diseases of spruce trees in Minnesota

Spruce Needle Rust

Photo by MNDNR Bugwood.org

This disease is caused by fungi from several species of the genus Chrysomyxa.

Colorado blue spruce, Picea pungens, white spruce, P. glauca, and black spruce, P. mariana, are all susceptible to the disease. Norway spruce, P. abies, is only occasionally infected.

Identification

Spruce Needle Rust

Photo by Gaston Laflamme, Natural Resources
Canada, Canadian Forest Service.

Stigmina

Photo by J. O'Brien
USDA Forest Service

Spore producing structures of Stigmina lautti on a spruce needle.

Biology

The spruce needle rust fungi live half of their life cycle on spruce needles and the other half on an alternate host in the Ericaceae family. In Minnesota labrador tea (Ledum groenlandicum), leather leaf (Chamaedaphne calyculata), and bearberry (Arctostaphylos uva-ursi) can all serve as alternate hosts for spruce needle rusts. In the spring, spores are released from the alternate host plant and infect young growing spruce needles if cool wet weather is present. In the summer months, these infected needles develop spore producing structures that release orange powdery spores. These spores can only infect the alternate host plant and do not reinfect the spruce. Infected needles often turn yellow and in most cases, fall off at the end of the growing season. The fungus that causes witches' brooms in addition to needle infection can overwinter within the infected spruce branches. All other spruce needle rust fungi overwinter in the alternate host plant.

Management

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