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
pathogen’s 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.
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