Cottonwood Rust caused by Melampsora medusae

From Bugwoodwiki

Anonymous. 1989. Insects and Diseases of Trees in the South. USDA Forest Service. Protrotection Report R8-PR16. 98 pp.

poplar rust Photo by Robert L. Anderson, USDA Forest Service, Bugwood.org Taxonomy Kingdom: Fungi Phylum: Basidiomycota Class: Urediniomycetes Order: Uredinales Family: Melampsoraceae Genus: Melampsora Species: medusae Scientific Name Melampsora medusae Thuem. Scientific Name Synonym Melampsora albertensis Arthur Common Name Synonyms cottonwood rust

Contents 1 Importance 2 Identifying the Fungus 3 Biology 4 Control

Importance

All sizes of cottonwood are affected, but cottonwood rust is particularly severe in plantations and nurseries. Heavy infection and subsequent defoliation may kill trees. The rust may also act as a predisposing agent to other diseases. Affected trees may be partially or completely defoliated.

Identifying the Fungus

Yellow or orange pustules, containing spores, form on the under-surface of the leaves in midsummer. These are replaced by dark brown fungal growths in the fall.

Biology

The orange pustules (uredia) are the summer reproductive state of the fungus. They are followed by dark brown pustules (telia) which develop in fall and winter. In the South, the alternate host (larch) is not present in the forest, and the fungal life cycle is reduced to the urediaurediospore cycle only. Some families are immune to rust infection and disease-free trees or groups of trees often occur in the midst of other heavily infected trees.

Control

Resistant varieties of cottonwood are used to minimize damage. Generally, no control is attempted in forest stands.