Pine Blister Rusts

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Basidiomycota
Subphylum	Pucciniomycotina
Class	Pucciniomycetes
Order	Pucciniales
Family	Cronartiaceae
Genus	Cronartium

Scientific Name

Cronartium comandrae

Scientific Name Synonyms

Cronartium pyriforme

Common Name

comandra blister rust

Compiled by Ned Tisserat, Colorado State University:

Cronartium species

Hosts

Comandra species

Pinus species

Ribes species

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Common Name	Fungus	Host	Alternate Host
White pine blister rust	Cronartium ribicola	Many species of five needle pine; primarily limber, bristlecone and whitebark pine	Ribes species; currants and gooseberry and Castilleja species and Pedicularis species
Comandra blister rust	Cronartium comandrae	Hard pines; primarily lodgepole and rarely ponderosa	Comandra umbellata
Pinyon blister rust	Cronartium occidentale	Pinyon and singleleaf pine	Ribes species; currants and gooseberry

Diagnosis and Damage

White pine blister rust infection is first apparent as yellow spotting of needles and formation of spindle-shaped swellings at the base of infected needles. As the infection progresses, diamond shaped cankers, orange in early summer when fruiting, are visible on young branches and stems. On older tissues, cankers have roughened, dead bark. Comandra blister rust symptoms include swelling, cracking, and elongate cankers on branches and stems. Resin is often associated with blister rust cankers. With comandra blister rust squirrels frequently gnaw off infected bark leaving a bark free canker. One to three years after infection, spermogonia appear as small drops of thick, sticky, reddish-orange liquid on the diseased bark. The following spring/summer orange aeciospores are released from pustules on the canker margin. Yellow-orange urediniospores and brown, hair-like telia are produced on the leaves of the alternate host in mid to late summer. Seedlings and young trees are most susceptible and are usually killed within a few years by stem cankers. Mature trees are commonly infected and have dead branches in cankered area and the crown thins and eventually dies creating a spike top. Rust cankers may result in growth losses, stem deformities, reduced cone and seed production, and mortality. Main stem cankers may weaken stems and increase risk of stem failure. White pine blister rust has only recently been discovered in Colorado, but is common in Wyoming and other areas. The extent of damage to the regions five-needled pines is currently unknown.

Biology and Disease Cycle

The fungus develops annually on the stems and leaves of the alternate host plant, infecting pine needles in late summer and early fall where it lives perennially in the inner bark of pine host. One to four years later, spermatia are produced on the bark of the pine, and the following spring aeciospores, which can travel further than 1000 km to infect the alternate host, are produced. The rust produces five types of spores, uredial, telial, and sporidial stages take place in the alternate host. spermatia and aeciospores, are produced on the pine host.

Management

In small, intensively managed areas, such as around nurseries, it may be feasible to eliminate the alternate host through practices such as maintaining dense stands, herbicide applications, fire, and pulling. Pruning of infected branches is effective in preventing the fungus from moving into the main stem. Harvest heavily infested stands and replant with non-susceptible species or with more trees than normal since some will die. There has been considerable success with breeding for resistance in white pines, for white pine blister rust, although little work has been done on the five-needled pines native to the region.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.