Western gall rust on hard pines

Abstract

Western gall rust (Pertdermium harknessiti Moore) causes trunk cankers and branch galls on most of the species of two-and threeneedled pines in the West.It is particularly common on lodgepole, ponderosa, and Digger pines.On these hosts its range extends from the Mexican border to Alaska, and on jack pine it is reported eastward as far as Quebec.Damage from gall rust in commercial stands occurs chiefly on lodgepole pine in the Rocky Mountains and, locally, in ponderosa pine from the Black Hills of South Dakota to the Pacific Northwest.Forest plantations, particularly of ponderosa and Scotch pines, have also been attacked severely.Unlike the introduced white pine blister rust, which can eradicate its pine hosts, gall rust is a native pathogen which occupies a fairly stable niche in living forests.It affects the form, lumber content, and growth rates 'of pines, and kills individual trees, but it is not known to wipe out whole stands.The Parasite Like all other rusts, Pertdermium harknessii 1s an obligate parasite: it does not grow in nature except in live hosts.In a pine gall or canker, thousands of fungus strands