Integrated Pest Management
Cytospora or Perennial Canker
Healthy tissue on the right with dead, cankered tissue on the left on a peach tree infected with Cytospora.
Cytospora producing small (1 mm) pimple-like bumps in which black fungal structures called pycnidia are embedded.
Cytospora canker (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.
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 cuts, 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 infections occur in the spring when daytime temperatures are 60 to 80F. The fungus continue to grow and produces spores during the warm weather months.
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. Water trees deeply, fertilize in spring, prevent iron chlorosis, apply mulch out to the drip line.
- Prune out and destroy dead or diseased twigs and branches. Do not leave stubs or narrow crotches. Prune in spring, but not when rain is imminent.
- 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 or white-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.