Sweet fern, stalactiform and Comandra rusts

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sweet fern blister rust Photo by Minnesota Department of Natural Resources Archive, Minnesota Department of Natural Resources, Bugwood.org Taxonomy Kingdom: Fungi Phylum: Basidiomycota Class: Urediniomycetes Order: Uredinales Family: Cronartiaceae Genus: Cronartium Species: comptoniae Scientific Name Cronartium comptoniae J.C. Arthur Scientific Name Synonym Peridermium comptoniae (Arthur) Orton & J.F. Adams

USDA Forest Service. 1979. A guide to common insects and diseases of forest trees in the northeastern United States. Northeast. Area State Priv. For., For. Insect and Disease Management., Broomall, PA. p. 123, illus.

Sweet fern rust (Cronartium comptoniae), stalactiform rust (Cronartium coleosporioides), and Comandra rust (Cronartium comandrae) are diseases of hard pines. Sweet fern rust is found in the northern United States, stalactiform rust occurs in the West and the Lake States, and Comandra rust if found in the West, Lake States, and South. These rusts may kill the tree outright or make it more susceptible to insects, decay, and wind breakage. The lumber cut from infected trees may be of low quality.

All three rusts require two hosts to complete their life cycles. The primary hosts of sweet fern rust are jack, Scots, lodgepole, ponderosa, pitch, and other hard pines. Sweet fern and sweetgale are the alternate hosts. Stalactiform rust infects jack, lodgepole, Jeffrey, and ponderosa pines. Cow-wheat, Indian paint brush, lousewart, and yellow-rattle are the alternate hosts. Comandra rust causes galls on jack, Scots, lodgepole, ponderosa, loblolly, and other hard pines. Bastard toadflax and northern Comandra are the alternate hosts.

Infection begins in the needles, and the fungus eventually moves into the stem. The sweet fern rust usually causes long swellings on the stems 1 to 2 years after infection. Aecia with orange-yellow spores are produced on the swellings in the early spring. Stalactiform rust produces a spindle-shaped canker that is difficult to distinguish from sweet fern rust in the initial stages. Several years after infection, long diamond-shaped cankers form on the main stem of the host. Aecia are produced at the margins of the cankers. Comandra rust causes elongated, slight swellings at the point of infection. The older cankers become cracked and pitted, are rarely swollen, and produce orange-red aeciospores in early spring.

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Photo by USDA Forest Service Archive, USDA Forest Service, Bugwood.org

Photo by Jane Taylor, USDA Forest Service, Bugwood.org