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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Bacterial Canker and Blossom Blast of Stone Fruit
Pseudomonas syringae pv. syringae
Updated Jul 02, 2025
Make a Positive Identification
- Bacterial canker is most serious on sweet cherry trees. It also affects almonds, apricots, peaches, plums, and prunes.
- Symptoms are most obvious in spring. They include blossom blast, leaf spots, and dormant-bud death. Rough, dark cankers on the trunk, limbs, and twigs ooze gum and may cause limbs to die back.
- High moisture and cool temperatures in spring favor the development of the disease. It is spread by splashing rain, wind, insects, infected bud wood or nursery stock.
Species: Bacterial Canker
Jay W. Pscheidt, Oregon State University
Dark cankered areas on trunks and branches develop and expand in early spring.
Amber-colored gum may exude from the cankers. They often girdle twigs and branches. This causes the branch to die above the canker.
Leaves on girdled twigs often turn yellow and fall off by late summer.
Species: Bacterial Canker
Iain McSwann, Oregon State University
The cambium at the canker is discolored and dead. Use a pocket knife to reveal this discolored tissue.
Species: Bacterial Canker
Jay W. Pscheidt, Oregon State University
In cold, wet weather bacterial canker can cause the death of flower buds. Blossoms may turn brown, shrivel, and cling to the tree. Infected buds usually start to die in February. In severe cases, 90% or more of buds on a tree may be killed.
Species: Bacterial Canker
Iain McSwann, Oregon State University
Sometimes leaves and fruit show spots of infection, but this is not common. Sunken spots may develop on young fruit.
Spots on leaves look water-soaked at first. Then they become dry and brown. They may drop out of the leaf, leaving a hole.
Infections may occur as the new growth emerges. The leaves may collapse entirely.
Bacterial Canker and Blossom Blast of Stone Fruit Benefits
- Bacterial canker and blossom blast is a plant disease that damages cherry and other stone fruit trees. It doesn’t have any benefit for people or the environment.
Bacterial Canker and Blossom Blast of Stone Fruit Risks
RISKS
- Bacterial canker and blossom blast causes severe damage to stone fruit trees, especially cherries.
- When conditions for disease development are good, up to 90% of buds may fail to open in spring.
Risk Card
Does it cause harm?
Adults & Children
None
Property
High
Pets
None
Annoyance
High
Environment
None
Action Recommended
Take Action?
Bacterial canker and blossom blast causes severe damage to stone fruit trees, especially cherries.
Do I need to take action?
You should take steps to prevent and control bacterial canker and blossom blast.
What if I do nothing?
- Severe systemic infections may cause decline and death of the tree.
- The disease will spread to other trees.
Prevent Bacterial Canker and Blossom Blast
Howard F. Schwartz, Colorado State University, Bugwood.org
Plant Resistant Cultivars when Available
- Cherry cultivars that are resistant: ‘Corum’, ‘Regina’, ‘Rainier’, ‘Sam’, and ‘Sue’ Also grafts on resistant Mazzard rootstock F12-1.
- Flowering cherries with some resistance: Prunus sargentii 'Rancho', P. yedoenis 'Akebono', and 'Kwanzan'.
Jay W. Pscheidt, Oregon State University
Give Trees Good Growing Conditions
Healthy, vigorous trees have less trouble with bacterial canker.
- Provide adequate fertilizer
- Adjust pH if needed, to 6.0 to 7.0
- Irrigate in dry weather, BUT avoid overhead watering
- Control weeds
- Avoid planting on shallow soils
Signe Danler, Oregon State University
Prune in Dry Weather or Summer
- Delay dormant pruning until January or February. Prune when rain will not occur for at least a week, and weather is dry.
- Summer pruning is even better. It should be done after harvest.
"Spring Orchard" by enneafive is licensed under CC BY 2.0.
Plant New Trees Away from Old Trees
- Old trees are a major infection source. The photo shows new trees planted with old, not a recommended practice.
Plant in areas not likely to suffer freezes
- This will prevent freeze damage that can allow infection.
Protect tree trunks to prevent sunscald
- This can damage the trunk and provide an entry point for the bacteria.
- Paint trunks with white latex paint, or use trunk guards.
Solutions for Bacterial Canker and Blossom Blast
Prevention
- Plant resistant cultivars.
- Give the trees good growing conditions.
- Prune in dry weather or summer.
- Plant new trees away from old trees.
- Plant in areas not likely to suffer freezes.
Non-chemical methods
- Prune out and destroy infected branches.
- Avoid injuries to tree.
Chemical methods
- Focus on cultural control tactics first. Then supplement with chemical control.
- Apply fungicides at the correct time of year for best control.
NEED HELP?
Consider a licensed pest control company. Learn How to Hire a Pest Control Company.
Your local Extension Specialist in Oregon and other states can suggest other methods.
Jump to
| Method | Does it work? | Is it safe? | Recommendation |
|---|---|---|---|
A Prune Out and Destroy Infected Branches |
Effective |
Low risk |
Recommended |
B Avoid Freeze Damage or Other Injury of Tree |
Somewhat effective |
Low risk |
Recommended |
C Remove Severely Infected Trees and Other Infection Sourcescted Trees |
Effective |
Low risk |
Recommended |
D Manage with Fungicides |
Effective |
Moderate risk |
Recommended |
|
E If Using Fungicides, Protect Yourself & Minimize Risks
|
A
Prune Out and Destroy Infected Branches
Non-Chemical Method
"File:Bacterial Canker on Cherry.JPG" by Rosser1954 is licensed under CC BY-SA 3.0.
Prune Out and Destroy Infected Branches
Recommended
Prune out cankered branches when weather is dry. This can be in summer, or during dry spells in late winter.
Cut a few inches below the canker to make sure it is completely removed.
Destroy diseased materials by burning, burying, or sending them to the landfill. Do not use as mulch or in compost.
Sterilize tools between cuts when pruning infected trees. Use 10% bleach or 70% rubbing alcohol or shellac thinner.
Cankers may be cauterized in the spring before bloom. Use a hand-held propane burner.
| Does it work? | Effective Removing infected plant parts reduces the spread of the disease. |
| How much effort? | Moderate effort |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
B
Avoid Freeze Damage or Other Injury of Tree
Non-Chemical Method
Signe Danler, Oregon State University
Avoid Freeze Damage or Other Injury of Tree
Recommended
Anything that weakens or injures the tree may allow it to develop cankers.
Do not plant where frost damage is likely.
If a freeze occurs during bloom or early fruit growth, cover smaller trees with frost cloth. Protective shelters may also be constructed.
Bacteria can be spread by wind, rain, insects, infected bud wood, and infected nursery stock. They can easily enter through wounds.
| Does it work? | Somewhat effective |
| How much effort? | Moderate effort |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
C
Remove Severely Infected Trees and Other Infection Sources
Non-Chemical Method
"File:Bacterial Canker - Gummosis on Cherry.JPG" by Rosser1954 is licensed under CC BY-SA 3.0.
Remove Severely Infected Trees and Other Infection Sources
Recommended
Remove trees that have the trunk or many branches girdled and killed by cankers.
Don’t allow trees to regrow from roots or trunks left after they are cut down.
Control weeds and destroy wild seedling cherry trees. These can be major sources of infection.
| Does it work? | Effective |
| How much effort? | Moderate effort |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
D
Manage with Fungicides
Chemical Method: Use with caution
iStock
Manage with Fungicides
Recommended
| Does it work? | Effective Fungicides used along with cultural controls can prevent bacterial canker and blossom blast. |
| How much effort? | Moderate effort Fungicides must be applied before plants develop disease symptoms to work. |
| What's the risk? | Moderate risk Using fungicides comes with real risks. ALWAYS read the entire label front to back. Review instructions even for brands you know. |
| Possible risk of exposure or harm from chemicals | Using fungicides includes some amount of risk. The lowest risk comes with using alternative methods. You may be exposed to a fungicide if you:
Follow directions closely to reduce risk. |
Some fungicides are available for home use and have anti-bacterial properties. They can be effective chemical treatments for bacterial canker. A few are listed below. These active ingredients are available alone or in products containing more than one. Look for these chemical names in the “Active Ingredients” section of product labels.
- Copper octanoate
- Copper ammonia complex
- Copper sulfate (Bordeaux Mixture)
Suggested pesticides are from the Pesticide Information Center Online (PICOL) Database. They are permitted for HOME use in Oregon. Read the label for application directions and effectiveness information.
ONLY professional pesticide applicators can use Restricted-Use Pesticides (RUP) that may be more effective. If you need further support, contact a licensed pesticide applicator.
Fungicide Application Tips
- Copper-based products have not worked well under conditions that favor disease development (moist and cool). Cases of resistance have also been reported.
- If you choose to use copper products, apply products before fall rains, during leaf fall. Apply again in early January just before buds open.
- Check for precise application timing on the label.
- Thorough coverage is needed.
- Alternate between chemical groups with different modes of action. The disease-causing bacteria may develop resistance if only one type of fungicide is used repeatedly.
- Using fungicides comes with real risks. ALWAYS read the entire label front to back. Review instructions even for brands you know.
- Consult a commercial pesticide applicator for treatment of trees over 10 ft. tall.
If Using Fungicides, Protect Yourself & Minimize Risks
Chemical Method: Use with Caution
Weston Miller, Oregon State University??
Why Is It Important to Read Fungicide Product Labels?
- They have detailed information on how to use the product correctly and legally.
- They contain information on potential hazards of the product.
- They provide instructions you should follow for poisonings and spills.
- Following label instructions helps you to minimize the risks and maximize the benefits.
Key Fungicide Safety Tips
- Read the entire label front to back.
- Follow the instructions.
- Review the instructions even for brands you know.
- Only apply the product where the label says it can be applied.
- Keep all fungicides in their original container.
The Label is the Law
ALWAYS read the label before using fungicide products. The label is a legal document that provides information on how to safely use the fungicide. It includes appropriate personal protective gear and application methods. This helps avoid harm to human health and the environment. Using a fungicide in off-label ways is illegal. It can result in legal enforcement actions.
READ THE LABEL & Follow Instructions
It has instructions to protect you and the environment.
- Labels are different for every product and they often change over time.
- Use a magnifying glass for small print.
- Pay attention to CAUTION, WARNING, and DANGER statements.
- Pay attention to the PRECAUTIONARY STATEMENTS.
- The law states you must read and follow fungicide instructions.
Protect Yourself
Eye, skin & lung irritants
- Wear the right protective gear. This often includes, but is not limited to: a long-sleeved shirt, pants, socks, closed shoes, safety glasses, and chemical-resistant gloves.
- Mix fungicide products outdoors or in a well-ventilated area.
- Wash hands after you mix or apply fungicides and before smoking or eating.
- Wash clothes worn while mixing and applying fungicides separately from all other laundry.
Protect Children & Pets
Children and pets are at risk if they eat or touch the plant before fungicides dry.
- Keep them away during and after applying fungicides (read label for how long).
- Remove toys and pet dishes from the yard before applying.
- Don’t track fungicide products into home on shoes or clothes.
Protect Pollinators
- Apply early morning or evening when bees are less active.
- Avoid spraying flowering plants, if possible.
- Don’t spray on bees or insects.
Storage & Disposal
- Store out of the reach of children and pets.
- Store in a cool and dry place.
- Never pour down any drain.
- If you mix too much, apply it rather than storing it.
- Don’t put fungicide containers in the trash unless instructed by the label.
- Take unused fungicides to a hazardous waste facility.
Call 1-800-CLEANUP (1-800-253-2687) to find out where to dispose of pesticides.
For the Portland metro region in Oregon, contact Metro’s Recycling Information. Call 503-234-3000, email or visit Metro’s website
More about:
About Using Pesticides on School Grounds in Oregon
If using pesticides on school grounds, there are special rules in Oregon. See School Integrated Pest Management (Oregon Department of Agriculture).
NEED HELP?
The National Pesticide Information Center (NPIC) can answer questions about pest control chemicals.
1-800-858-7378 or npic@ace.orst.edu
Consider using a licensed pest or weed control company. Learn How to Hire a Pest Control Company.
Your local Extension Specialist in Oregon and other states can suggest other methods.
Content provided by Weston Miller, Signe Danler and Jeremiah Mann. Pesticide safety information edited by Kaci Buhl.
Peer review facilitated by OSU Department of Horticulture.
BACTERIAL CANKER REFERENCES
Cherry (Prunus spp) Bacterial Canker
PNW Pest Management Handbooks
Bacterial Cankers
Washington State University Hortsense
Bacterial canker
University of California IPM Program
Managing Diseases and Insects in Home Orchards
Oregon State Extension