Stem Rusts


Comandra Rust - Cronartium comandrae

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Comandra rust canker on the main stem of pine.

Comandra rust

Branches infected with Comandra rust.

aeciospores of Comandra rust

Microscopic view of aeciospores of Comandra rust. The shape of these aeciospores ,tadpole or snowshoe-shaped, is different from those of other stem rusts. 

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Alternate host - Comandra umbellata

Comandra rust

Uredinia followed by telia form on the lower leaf surdace of Comandra.

Sweetfern Rust - Cronartium comptoniae

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Sweetfern rust on main stem of pine. Infection is restricted to the lower bole of the tree.

sweet fern rust

Cross section from the trunk of a jack pine infected with sweetfern rust showing distorted and resin filled main stem.

sweet fern rust

A cross section of an infected tree showing decay by Porodaedalea pini (old name is Phellinus pini). Sweetfern rust cankers serve as an entrance point for some heartrot fungi and decay can extend throughout the main stem. Usually these decay fungi attack old growth trees but sweetfern cankers produce resinous reaction wood and decay fungi enter the trees as early as 5-8 years old.

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Seedlings infected with sweetfern rust. The top seedling is at the stage where pycnia are produced. The bottom seedling has aecia.

Sweetfern in lab

Sweetfern, Comptonia aspenifolia, is an alternate host for this rust.

sweet fern rust

Sweetfern leaf with uredinia is on the right (yellowish round areas) and leaf with telia on the left (brown hair-like structures). Uredinia form in early summer and telia form in last summer/fall.

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Sweet gale, Myrica gale, is another alternate host.

Sweet gale with telia

Sweet gale leaf with telia. Yellow droplets are exudates from the leaf and not associated with the rust.

Stalactiform Rust - Cronartium coleosporioides

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Main stem infection on pine.

branch canker caused by Stalactiform rust

Branches infected by Stalactiform rust. 

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Cowwheat, Melampyrum, is an alternate host.

Stalactiform rust on cowwheat

Uredinia followed by telia form on the alternate host. This cowwheat leaf has telia stating to grow.

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Indian paint brush, Castilleja, is another alternate host.