Western gall rust
Damage, symptoms and biology
The fungus causes a gall that encircles the stem or bole of infected trees. White blisters develop at the site of the gall, just beneath the bark. In spring, the blisters burst and orange spores are released which end up infecting other pines. Rupturing of the blisters results in desiccation of the underlying living bark, killing the bark area around the gall. Following the death of the water-conducting tissues, some needles will die in the lower part of the branch, near the distal portion of the gall.
Damage is not significant on mature trees where most infections occur on branches. Branch galls do not result in serious growth losses. However, infections on young trees more often result in main stem galls that can cause stem malformations and predispose the tree to breakage in high winds or under heavy snow loads (Figs e, f).
A large numbers of galls reduces the aesthetic appearance and value of ornamentals and Christmas trees.
Unlike the other important stem rusts, E. harknessii does not require an alternate host to complete its life cycle. Infection occurs directly from pine-to-pine. This allows rapid intensification of the disease when conditions optimal for infection occur. However, such conditions only occur every several years, resulting in "wave years" of infection and gall formation.
Pruning the infected branches prior to spore production is a good means of control. Rodents feed on the galls in winter, and this may result in a high level of mortality some years.
Canadian Forest Service Publications
Information on host(s)
Austrian pine, mugho pine