Western Gall Rust of Pine

Taxonomy

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

Scientific Name

Endocronartium harknessii

Common Name

western gall rust

Western Gall Rust of Pine (Endocronartium harknessii)

Compiled by Ned Tisserat, Colorado State University:

• Source1
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• Source3

Host

Pines (Pinus species)

Affected tree species include a number of native pines, including ponderosa, pinyon, lodgepole, as well as the introduced Scots and mugo pines.

Symptoms

The disease causes the appearance of spherical galls on the branches and limbs of pines of all ages. These galls persist but are most visible in the spring when the surface ruptures to release bright orange spores. Galls are most commonly found on branches, but can be found on the main stem; this is more common in certain species, most notably jack and lodgepole pines. As galls enlarge, they cause branch dieback and often cause the host to develop witches' brooms. Trunk or 'hip' cankers are common on lodgepole pine where they do not look like a typical gall but a diamond-shaped canker.

Impact of Disease

In the Rocky Mountain region the disease is common in stands of lodgepole and ponderosa pines and can be serious in Christmas tree plantations and windbreak plantings. Tree mortality due to western gall rust occurs most frequently in plantations of seedlings, where the likelihood of a gall girdling the entire stem is highest. In mature trees, loss of growth is more likely to occur, but mortality can occur in extreme cases. Wind breakage often occurs at the gall on stems so these trees should be considered hazardous if there are targets for the tree if it should fail.

Life Cycle of the Pathogen

E. harkenessii is spread to non-infected trees by means of spores produced in the galls of infected trees. These spores, produced in the spring, are released when the gall surface ruptures. This dispersal occurs in May and June and allows the spores to infect the current year's shoots. Galls form the year after infection occurs, usually in the summer; the time of infection is thus 2 years in most cases. Whereas many rust fungi require an alternate host to carry out their life cycles, E. harkenessii does not; for this reason, it is sometimes called pine-pine gall rust. Existing galls continue to produce spores every year, making this disease increasingly capable of causing future infection as time goes on. It is this ability, coupled with the ability to directly infect other pines, that makes this disease capable of causing tremendous loss to commercial growers.

Management Approaches

Cultural Management Practices

Since spores require wet plant surfaces and cool temperatures to germinate, prolonged periods of cool, wet weather promote the greatest degree of infection. Large numbers of susceptible trees in a given locale (i.e., pure stands or plantations) allow the disease to spread at a high rate. This disease is very difficult to control because of its high rate of infection and the latency period between infection and expression of the symptoms. Removing infected trees has limited effect, since latent infections from the previous year are invisible and therefore cannot be controlled. In any nursery situation, acquisition of clean stock is the best means of prevention.

References

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.