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Cytospora or perrenial canker of fruit and shade trees Page 1 of 2
Utah Plant Disease Control No. 15
Revised February 1993
Cytospora or Perennial Canker
of Fruit and Shade Trees
Cytospora Canker or Perennial Canker is one of the most common diseases of fruit and shade
trees in Utah. This canker disease is caused by a fungus called Cytospora. There are several
species of Cytospora that attack many different hosts, but the symptoms and control are
essentially identical for all of them. The host range of Cytospora is broad, including peach,
cherry, apricot, apple, poplar, willow, birch, aspen, and many other broadleaf trees. Stone fruits
are more susceptible to perennial cankers than are pome fruits.
SYMPTOMS
Cytospora is considered a weak parasite and invades only weakened or stressed trees. It
gains entry through injuries in the bark caused by machinery, sun scald, frost, pruning wounds,
broken branches, mechanical shakers, and insect injury. Cankers on trunks or branches are
sunken and range in color from brown to gray depending on the host species. The canker
expands slowly over a period of months or years and may eventually girdle the branch,
causing it to die. The fungus may produce small (1 mm) pimple-like bumps in which black
fungal structures called pycnidia are embedded. The presence of pycnidia can be confirmed by
slicing the bark with a knife where raised areas are evident. Pycnidia are quite common and
obvious on mountain ash, cherry, and birch. During warm, wet weather, brown to orange-
colored masses of spores (analogous to seeds) are extruded from the pycnidia in a tendril-like
mass. These spores are carried by rain or blown by wind to susceptible sites where they cause
new infections. Optimum conditions for Cytospora infec-tions occur in the spring when daytime
temper-atures are 60 to 80F. The fungus continue to grow and produces spores during the
warm weather months.
CONTROL
Preventing infection is the best way to control Cytospora. There are no fungicides which are
effective in controlling the pathogen once it is in the tree. No single method of control can be
used to prevent this disease; therefore, it is necessary to use several of the methods described
below to maintain healthy plants.
. Maintain high tree vigor. Trees should be watered deeply during dry summer months to
prevent drought stress. Fertilize in the spring to keep trees vigorous. Avoid late summer
applications of nitrogen because it stimulates growth in autumn which does not harden
off before winter. Trees stressed with iron chlorosis are particularly susceptible to
Cytospora infections. The roots of birch trees are quite shallow and are damaged or
killed by high soil temperatures and drought on south or west facing slopes. Keep soil
cool and moist by frequent irrigation.
. Prune out and destroy dead or diseased twigs and branches. Do not leave stubs or
narrow crotches. prune on a regular basis so that large cuts will not be necessary.
http://www.extension.usu.edu/ipm/disfact/upd 15.htm 8/8/2003
. Cytospora or perrenial canker of fruit and shade trees
Page 2 of 2
Pruning wounds are susceptible to infections, so prune in the early spring and not when
rain is imminent. Treat pruning cuts larger than ane inch in diameter with a paint of 1
thiram or 3-10% Copper Naphthenate. Asphalt pruning paints are not effective. An
application of benomyl as a spray immediately following the pruning of a fruit orchard
may reduce new infections. Benomyl is no longer registered for use on ornamental trees.
. Prevent sunscald by painting the trunk of thin-barked trees with white latex paint. The
trunks of newly planted trees should be wrapped with burlap orwhite-colored tree wraps
to prevent sunburn. These techniques will also reduce winter damage which occurs on
the southwest side of trunks.
. Control borers and other wood-attacking insects.
. Avoid mechanical injury to tree with lawn mowers, lawn trimmers, ladders, shakers, or
other equipment.
. Woodpiles are an important source of inoculum for the disease. To prevent infections on
nearby trees, destroy any wood that appears to have pycnidia.
Sherman V. Thomson/ Extension Plant Pathologist
Scott C. Ockey/Plant Disease Diagnostician
Listing of commercial products implies no endorsement by the authors or the Utah State Cooperative Extension Service. Criticism of products not
listed is neither Implied nor intended. Persons using such products are responsible for their use according to the current label directions of the
manufacturer. Pesticide labels are legal documents, and it is a violation of federal and state laws to use a pesticide Inconsistent with its labeling. The
pesticide applicator is legally responsible for its proper use. Always read and follow the label.
http://www.extension.usu.edu/ipm/disfact/upd 15.htm 8/8/2003