Michigan State University Extension
Ornamental Plants plus Version 2.0 - 00001687
01/01/98
The Russian olive is so susceptible to the canker and dieback caused by Phomopsis elaeagni that it is no longer considered suitable as an ornamental shrub or small tree.
Symptoms: Symptoms are a typical dieback of branches in the uppermost portion of the canopy. Young green shoots may wilt and die and leaves remain withered and attached. The sapwood below the dead, orange-brown bark turns black, and the discoloration extends beyond the canker. Cankers are oval and depressed; most are 1 to 6 inches long.
Cause: The spores of the fungus are rain splashed and generally infect broken thorns, branch stubs and bark wounds. The fungus will infect even healthy, vigorously growing plants. Infection can occur throughout the growing season whenever rain and wounds are present. Spores ooze from fruiting bodies on the dead, orange-brown bark whenever rains wet the branches.
Control: Russian olives with dieback might best be removed and replaced with the canker-resistant autumn olive. Otherwise, prune out dead branches and revitalize the root system as described under General decline and dieback. No fungicides are effective for control of Phomopsis on Russian olive.