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 tadpole or snowshoe-shaped aeciospres are different from those of other stem rusts. 

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Alternate host is Comandra umbellata - this is a dried speciment of the plant

Comandra rust

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


The Comandra plant flowering.

Telia on Comandra

Uredinia and telia form on the bottom of the Comandra leaves. The brown hair-like structures seen here are telial columns.

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.

Sweetfern rust xsec

A cross section cut thru the canker showing the many lesions and also the reaction wood (dark colored areas) that formed in the wood behind the cankers

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.

Sweetfern infected seedlings

Sweetfern rust infected seedlings. Pycnia would form on the young cankers.

Aecia of sweetfern rust on seedlings

Seedlings infected with sweetfern rust with aecia forming. Aecia form one year afterthe pycnia.

Sweetfern rust producing aecia in the field

Pycnia and aecia also can form on the edges of older cankers. This photo show aecia, yellow areas, producing aeciospores in the forest on a canker at the base of a tree. 

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.


Sweet gale, Myrica gale, is another alternate host for this rust.

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.


A cowwheat plant in the forest

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.