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Russian Olive Cankers

Cankers occur on a great deal of the woody plant material we see at the Plant Clinic. Cankers are generally caused by secondary, or stress, pathogens and are only a part of the problem. They are merely a clue that something more is wrong.

A canker is a dead area, usually on a woody plant, that often results in an open wound. Starting as a small, sharply delimited, usually round-to-oval or elongate lesion, a canker might enlarge and girdle the cane, twig, limb, trunk, or root. The canker indicates the area of the cambium that has been killed; the sapwood underneath is generally brown or black. The canker itself may be thickened and rough or it may appear sunken. On very tightly barked trees, a color difference in the bark may be all that delineates the canker. Cutting into the affected area with a knife will reveal that the cankered area has brown inner wood, while the healthy area is white or green.

Russian olive trees suffer from many cankers. The principal ones are caused by such fungi as Phomopsis, Lasiodiplodia (Botryodiplodia), Nectria (Tubercularia), and Phytophthora.

In Illinois, the most important canker by far is Phomopsis. Unlike other canker fungi, Phomopsisis an aggressive pathogen that can attack and kill vigorous trees. Trees seriously injured by drought, hail, or ice are subject to decline and more rapid spread of the disease. Phomopsis-infected trees often appear ragged, with several dying or dead twigs and branches. Current-season twigs and small branches often wilt and die, with the dead, withered leaves hanging on for some time. Oval-to-elongate, sunken cankers are most evident on the large branches and trunks.

Diseased bark on Phomopsis cankers varies from orange- brown to dark reddish brown. Ridges often form around the canker margins. Branches girdled by the enlarging and encircling cankers wilt and die. The white sapwood beneath the cankers turns dark brown to black and extends beyond the margins. Minute, slightly raised, rounded pustules of the Phomopsisfungus are embedded in the dead, cankered bark.

Avoid all unnecessary bark wounds because they are the pathogenís main avenue of entry. All seriously infected trees showing dieback should be cut off near the ground and destroyed, preferably by burning. More details on this disease can be found in Report on Plant DiseasesNo. 606.

Author: Nancy Pataky

 

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