Spruce broom rust
Chrysomyxa arctostaphyli

This heterodemicycyclic rust on the Spruce (aecial stage) is Chrysomyxa arctostaphyli. Also called spruce broom rust, this can not survive on spruce alone but alternates between spruce (Picea) and Kinnikinnick (Arctostaphylos uva-ursi).

This beautiful sample has needles covered with the fruiting structure of a heterodemicyclic rust. The hetero portion of this term refers to the fact that this rust alternates between two different plants, in this case spruce and Kinnikinnick. The demicyclic portion of the name refers to the number of stages that make up the cycle of this rust.

Rusts are strange organisms. They may have up to six different spore states that may alternate between two unrelated groups of host plants. Some rusts can complete their life cycle on one plant, but our spruce broom rust requires two hosts as indicated above. Some rusts that invade spruce use azaleas and rhododendrons as their alternate hosts. Our rust causes purple leaf spots in early spring on the underside of the leaves of Kinnikinnick, Arctostaphylos uva ursi. The spores produced on Kinnikinnick then move in air currents to the spruce where additional stages of this disease occur. In most cases, the application of a fungicide to control rust is possible. However, control is best achieved by the eradication of one of the hosts involved. Control would include the removal of all rust brooms and elimination of kinnikinnick in the area.

Broom rust is perennial and systemic in large witches' brooms; the fungus fruits abundantly on all the broom's current year's needles which are yellow in summer and die and are shed in fall. This causes the broom to appear dead during winter.

Rust brooms on spruce are commonly associated with spiketops, dead branches, bole deformation, loss of increment, and mortality. Phellinus pini (formerly Fomes pini) is reported as the most important decay fungus that invades rust brooms.

Spruce brooms not caused by rust will retain their normal dark-green foliage throughout the year and loose few needles in the fall.

Additional Photographs on Spruce Broom Rust can be found at http://www.forestpests.org/subject.html?sub=735