On older trees, "P. cactorum" causes the formation of sap exuding dark colored cankers on the trunks of trees, as well as leaf size and number reduction, chlorosis, and dieback of branches. The diagnosis of a "P. cactorum" infection of trees, is based on the identification of symptoms, in particular the oozing cankers, and confirmation of symptoms in a diagnosis lab or utilization of a field ELISA detection kit. "P. cactorum" can be a major problem in apple orchards, as it can cause crown, collar, and root rots in apple trees. When infecting apple trees, the organism can attack through wounds either above or below the soil line, impairing phloem and root function, and causing stunting, foliar disorders, and death after several years. Furthermore, because the pathogen causes damage to the phloem of the tree, one diagnostic method is to check for necrotic phloem tissue at the base of the tree which will be orange to red-brown in the early stages and dark brown in the later stages of infection.