Cronartium harknessii

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.

Life Cycle ...

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 ...

Western Gall Rust of Pine (Endocronartium harknessii)