Peach canker is a fungus disease common on apricot, prune, plum, and
sweet cherry trees as well as on peach trees. The disease is common
in peach orchards and is a frequent cause of limb dying and death of
peach trees. Other common names for peach canker are perennial canker
and Valsa canker. The fungi that cause this disease enter the plant
through wounds. Infection results in dead and weakened twigs and
branches, and in reduced yields.
Symptoms
The first symptoms appear in early spring as gummy drops of sap around
wounded bark. The diseased inner bark begins to break down, causing
the cankered surface to appear depressed. Black specks, which are
fungal spore producing bodies, appear on the bark surface or under
the bark tissue. During wet periods spores ooze out of these fungal
bodies in tiny orange or amber colored, curled strands. During the
summer, healthy bark (callus tissue) grows over the edges of the
narrow, oval shaped cankers. In the fall, the fungus resumes growth,
attacking and killing the new callus tissue. Over a period of years,
a series of dead callus ridges form as the canker gets larger.
Eventually, the canker may completely surround a branch. The portion
of the branch beyond the canker then dies. Large amounts of gum are
usually produced around cankered areas. Peach canker is often
confused with other problems which cause cankering and gumming. Among
these are bacterial canker, insect borer injury and mechanical
injury. When insects are involved, chewed-up wood dust is usually
visible under the gum. Mechanical injury can often be verified by
carefully reviewing recent operations in the area.
Causal Organism
Peach canker is caused by the fungi, Cytospora leucostoma and
Cytospora cincta. These fungi are weak pathogens and generally do not
attack healthy, vigorous peach bark. Winter injury, insect damage,
and mechanical injury are common types of wounds serving as entry
points. The fungi survive the winter in cankers or in dead wood.
During spring and summer, spores produced in the cankers are spread
by wind and rain to wounds on the same or nearby trees. The spores
are not blown over long distances in the wind. Infection and canker
development depend on temperature and the species of fungus involved.
Cytospora cincta is favored by lower temperatures than Cytospora
leucostoma. Because of the manner of infection and development of
this disease, no single control measure is adequate. Most known
control methods act indirectly by reducing points of entry or by
reducing the level of inoculum. Fungicides are generally ineffective
for controlling this disease.
Control can be facilitated by following these guidelines:
Control
- Prune young trees carefully to avoid weak, narrow-angled
crotches. Narrow-angled crotches are frequent sites of breakage and
winter injury.
- Delay pruning until early spring. This promotes quick healing.
Remove cankered branches and dead wood while pruning. Do not leave
protruding pruning stubs. Cut flush to the next larger branch.
- Eradicate cankers and remove badly cankered limbs, branches or
trees. Burn or remove all cankered limbs soon after pruning. These
limbs or branches serve as a reservoir for the disease causing fungi.
Sanitation is critical, especially during the early life of the
orchard.
- Do not plant new peach trees near established trees with
canker.
- Avoid mechanical and insect injury.
- Promote vigorous, healthy peach trees with proper fertilization,
pruning, and water.
- Do not over-fertilize late in the season. Winter injury is more
common on these trees because winter hardening is delayed.
- White latex paint applied to the southwest side of trunks and
lower scaffold branches may help avoid cold injury.
- Maintain a good control program for other diseases and insect
pests, especially borers.
For the most current spray recommendations, commercial growers are
referred to Bulletin 506-A2 "Ohio Commercial Tree Fruit Spray Guide,"
and backyard growers are referred to Bulletin 780 "Controlling
Diseases and Insects in Home Fruit Plantings." These publications can
be obtained from your county Extension agent or the Extension
Publications Office, The Ohio State University, 385 Kottman Hall,
2021 Coffey Road, Columbus, Ohio 43210-1044.
-----------------
All educational programs conducted by Ohio State University Extension
are available to clientele on a nondiscriminatory basis without regard
to race, color, creed, religion, sexual orientation, national origin,
gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and
Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-1868
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