Cytospora or Perennial Canker
- Broadleaf 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. 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 wounds, broken branches, mechanical shakers, and insect injury. The canker expands slowly over a period of months or years and may eventually girdle the branch, causing it to die. 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. 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 80°F. The fungus continue to grow and produces spores during the warm weather months.
- Sunken cankers on trunks or branches that range in color from brown to gray
- Small pimple-like bumpsin which black fungal structures (pycnidia) are embedded
- Brown to orange colored masses of spores extruding from pycnidia
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. Pruning wounds are susceptible to infections, so prune in the early spring and not when rain is imminent. Treat pruning cuts larger than one 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 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.
- Woodpiles are an important source of inoculum for the disease. To prevent infections on nearby trees, destroy any wood that appears to have pycnidia.