Western gall rust—Endocronartium (=Peridermium) harknessii
The fungus infects branches and trunks of two- and three-needle pines. Hosts include Aleppo, Bishop, lodgepole, Monterey, ponderosa, Scots, and shore pines.
Often infections are within 10 to 20 feet from the ground. Galled stems may exude sap. Galls sometimes become colonized by other fungi or insects or chewed by small mammals. Beyond the galls, foliage may become stunted and bushy, and the terminal may die back or break off.
Flagging of branch terminals (needles dying and turning brown) resembles damage from pitch canker infection and certain insects (e.g., twig-feeding beetles). Western gall rust infection can readily be distinguished from other diseases and insect damage by the presence of the galls, when young each 2 to 3 inches in diameter, near the dead terminals.
In spring, young galls develop orange spores on their surface. The spores are spread from pine to pine by wind and if shoots are wet infect the terminals of the youngest branches or the mainstem terminal. Needles do not become infected. The fungal germ tube (outgrowth of a spore) directly penetrates the host cuticle and epidermal cells to develop a perennial infection in living tissue. Infection of the cambium stimulates gall formation.
The fungus can remain alive as long as the infected host tissue lives, which may be from a few to many years on branches to the life of a long-lived tree for basal mainstem infections.
The fungus causes spherical swellings or galls, cankers, and dieback on branches in two- and three-needle pines. Some pines develop rust infection at the base of their mainstem. These trees if they live to an old age can develop a large depression on one side the lower trunk, called a hip canker.
Prune and dispose of infected branches during October to January. Large galls on major limbs or the trunk can lead to structural failure; consider removing and replacing trees that may be hazardous. For more information, consult the California Forest Insect and Disease Training Manual and Western Pines and Western Gall Rust .