Last Review/Updated: January 6, 2003

Western gall rust (Endocronartium harknessii (J.P. Moore) Y. Hirat.) is one of the most common and destructive disease of hard pines, and is economically important in high value plantations, tree farms and nurseries. Unlike other stem rusts, this species can directly and more rapidly infect other pine trees without going through an alternate host. Airborne spores infect the green tissue of young shoots and cause the wood to swell into galls (globe-shaped clumps).

Primary Hosts and Distribution

• Jack pine (Pinus banksiana Lamb)
• Lodgepole pine (P. contorta Dougl. var. latifolia Engelm.)
• The rust generally affects young pines throughout the province.

Disease Cycle

Unlike other pine stem rusts, this disease can infect directly from pine to pine without going through alternate host plants. Spores are produced on the surface of galls between May and July. They become airborne and infect the green tissue of young shoots. Swelling occurs within the growing season of infection, and some spore production occurs one year after infection. Most spore production occurs in the second year and it continues every year on the surface of the expanding gall until the death of the gall.

Detection and Damage

Look for the following signs and symptoms:

• Branch and stem globe-shaped perennial galls caused by swelling of the wood rather than the bark are conspicuous and easy to recognize;
• Orange-yellow spores are produced within the bark tissue of the gall for 5 to 6 weeks every spring.

This disease often kills small trees that have main stem galls. However, this disease does not usually kill trees; if the tree has a main stem gall, it may not grow to become a crop tree because of its poor growth and deformed main stems. Breakage of main stems often occurs at the gall because of the weakening of stem tissue at the gall. Branch galls do not significantly affect the overall health of the infected trees but help spread the disease.

Management

Some management procedures include:

• Surveying young stands;
• Identifying and removing trees with main stem galls during early and precommercial thinning operations;
• Not growing seedlings in outdoor nursery beds located close to stands of pine infected with significant amount of western gall rust.
• Culling seedlings with stem swellings before transplanting.