What Causes Death of Russian Olive Trees?

Verticillium Wilt

• Russian olive will grow in U.S. Department of Agriculture plant hardiness zones 3a through 8b; however, verticillium wilt may kill it in poorly drained sites or in the humid climate of the eastern United States. Verticillium fungi infect roots, then move upward, plugging a tree’s vascular system with a gum-like substance. Symptoms include discolored sapwood, yellowing leaves and defoliation. There are no proven cures for the disease. Your only option is to prune out infected parts and apply fertilizer that is low in nitrogen.

Phomopsis Arnoldiae

• The fungus Phomopsis arnoldiae enters the bark of Russian olive trees through wounds in their bark. Small reddish brown to black cankers appear on branches. As the cankers get larger, they get darker in color and sink into the wood where they split open. Sap may ooze from their edges. When the cankers circle a branch or trunk, leaves wilt and branches die. There are no known chemical cures for Phomopsis infection. Prune at least 6 inches below the canker and dispose of diseased branches.

Getting to 'Em Early

• While Russian olive trees rarely escape cultivation in eastern states, it is wildly invasive in western states. You can kill Russian olive seedlings or saplings by pulling them out of the ground with special weed pulling tools. You can also chain them and pull them out with a tractor or use a bulldozer to gouge them out. Cut off any exposed roots below ground level. These methods are all best done when the ground is moist, and doing this one time will not get rid of them completely. Watch them. They will inevitably return, forcing you to repeat your chore.

Killing the Undead

• If you’re faced with an invasion of mature Russian olive trees, think of them as zombie trees; they are the undead. Just when you think you’ve gotten rid of them, they’ll likely come back, forcing you to repeat the process of trying to kill them. If a Russian olive trunk is less than 8 inches wide, cut it down as close to the ground as possible and spread herbicides containing the active ingredients glyphosate, 2,4-D, imazapyr, picloram or triclopyr on the stump. If the trunk is less than 4 inches wide, cut it down and mow the stumps with a mulching tractor, then spread triclopyr on the stubs within five minutes. You can also use a chain saw to strip the bark from the tree near the ground then spread the sapwood with one of the herbicides.