In addition to Verticillium wilt, one of the more serious of the diseases affecting this species, Phomopsis canker , another fungal disease, is now a serious problem in some areas. In Wisconsin, it has apparently reached epidemic proportions, with the consequences that some consider Russian-olive to have outlived its usefulness as a cultivated species in the region. This disease has also caused extensive damage in the eastern half of Kansas. The disease is manifest as reddish-brown to black areas of canker on smaller branches, often with small dark fruiting structures of the fungus on the diseased bark. When the cankers girdle the branch, water flow is restricted with the result that leaves wilt and branches die back.
Cankers tend to form lower down first and then progress upwards throughout the canopy.
The disease is difficult to control but pruning during winter and dry summer months and appropriate disposal of branches slows the progression of the disease. R ussian-olive Decline and Gummosis have had an increasingly important impact on this species in Colorado. Affected trees exude amber-coloured gum from the bark. The precise causes of this condition is uncertain and may, in part, be related to fungal infections. Gums are exuded by Russian-olive when plants are under stress.