Pine-pine gall rust, also known as western gall rust, is a fungal disease of pine trees. This plant disease is caused by Endocronartium harknessii (asexual name is Peridermium harknessii), an autoecious, endocyclic, rust fungus that grows in the vascular cambium of the host. Pine-pine gall rust is found on pine trees (Pinus spp.) with two or three needles such as ponderosa pine, jack pine, and scots pine. The disease is very similar to pine-oak gall rust, but its second host is another Pinus species. The fungal infection results in gall formation on branches or trunks of infected hosts. Gall formation is typically not detrimental to old trees but has been known to kill younger less stable saplings. Galls can vary from small growths on branch extremities to grapefruit sized galls on trunks.