Cytospora Canker

Cherry, apple, peach and plum trees are all susceptible to a fungal disease called Cytospora canker.

Flagging of a cherry branch girdled by Cytospora leucostoma. Photo by Franz J. A. Niederholzer. (UCANR)

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Cytospora canker is a collection of symptoms caused by several species of Cytospora fungi. This disease is also seen in ash, birch, cottonwood, elm, maple, willow, spruce and other conifers. Some Cytospora fungi are host-specific, while others can infect several different tree species. Sadly, Cytospora canker can be fatal.


Cytospora canker lifecycle

Cytospora canker fungi infect trees and shrubs that are stressed or weakened by injury, frost damage, drought, or pests. Spores are carried by wind and rain. Infection can occur at any time of year, but is more likely during dormant periods, when trees are less able to defend themselves. Fungal spores enter through tiny wounds in the roots or bark and begin growing in the xylem and phloem. Eventually, the branch is girdled, blocking the flow of water and nutrients, and the branch dies. If infection occurs in the trunk of the tree, the tree will die.

Splitting cankers, rough callus tissue, and hardened resin are signs of Cytospora canker (UMass Extension)

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Cytospora canker symptoms

The first sign of Cytospora canker is often the random die off or flagging of tree or shrub branches. Closer inspection reveals cankers on stems and branches. These cankers tend to be long and narrow and may or may not  be sunken or discolored. These fungi grow so rapidly that discoloration and sunken areas do not always have time to form, but the bark may split along the edge of the cankers as the tree tries to defend itself. These cracks allow for the formation of a callus that blocks the fungi from entering. Sometimes this works, and sometimes it doesn’t. In some cases, girdling occurs without any visible cankers. Gumming may also occur. Gumming is when stems and fruit ooze out a sticky sap. This is another form of tree defense.


If you cut into a diseased stem, you may notice discoloration and a funky smell. If you see tiny black spots, you are looking at fruiting bodies of the fungi.


Cytospora canker prevention and control

The easiest way to prevent Cytospora canker is to keep your trees and shrubs healthy in the first place. Healthy plants are less likely to become stressed enough to be vulnerable to infection by fungal spores in the first place. ​

Signs of Cytospora canker (top to bottom): hardened resin, callus tissue and small, black-colored spore bearing structures (UMass Extension)

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Since drought and flooding are the most common conditions that make trees susceptible to Cytospora canker, regular irrigation during summer and proper drainage in wetter months can prevent infection. These other tips can help prevent Cytospora canker:

• prune for structure and good airflow and to prevent broken branches
• avoid digging around tree and shrub roots
• prevent injuries from weedwackers and mowers
• control insects, such as scale and borers
• select species suitable to your microclimate
• conduct a soil test to see if potassium deficiency or other nutrient imbalances are negatively impacting your tree(s)
• whitewash bark to prevent sunburn damage
• space plants at proper distances from one another
• only install healthy, disease-free plants

Once infection occurs, remove any affected stems and branches by cutting close to, but not damaging, the branch collar. Be sure to disinfect your cutting tools with bathroom cleaner or ethyl alcohol between each cut. Then apply a fungicide to each cut. Do not use any other wound dressing, as these treatments can trap spores and moisture where you least want them.


There are no known chemical controls for Cytospora canker, so keeping those trees and shrubs healthy is your best bet.