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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Apple Scab
Venturia inaequalis
Updated Dec 17, 2024
Make a Positive Identification
- Apple scab is a fungus that causes scabby lesions on apple leaves and fruit.
- It may cause trees to drop their leaves.
- It overwinters in infected plant debris.
Species: Apple scab
Signe Danler, Oregon State University
Scab first appears as tiny yellow, or chlorotic, spots on leaves. They enlarge and turn dark olive-green, then black. Leaves may become distorted, puckered, and mottled. Severely affected leaves often turn yellow and drop early. This defoliates and weakens the tree.
Species: Apple scab
Margalob, CC BY-SA 4.0, via Wikimedia Commons
Scab spots on fruits begin as small, raised, brown or black circular areas. As fruit develops, scab spots enlarge. The central areas become brown and corky. Deep cracks may develop. Severely infected fruit becomes misshapen and usually drops from the tree.
Species: Apple scab
University of Georgia Plant Pathology , University of Georgia, Bugwood.org
Late-season infections may not show on fruit until they are in storage. There they develop small black "pinpoint" scab spots. This may be tolerated in backyard trees. Peeling the fruit will remove the pinpoint-sized scab lesions.
Apple Scab Benefits
- Apple scab is a plant disease that harms susceptible apple fruit and trees. It doesn’t have any benefit for people or the environment.
Apple Scab Risks
- Apple scab causes damage to leaves and fruit.
- Fruit is unsightly. It may be distorted, severely blemished, and inedible due to poor texture.
- Leaves may drop and weaken the tree.
Risk Card
Does it cause harm?
Adults & Children
None
Property
Low
Pets
None
Annoyance
Some
Environment
None
Action Optional
Take Action?
Apple scab impacts the fruit and health of apple trees. It can destroy an apple crop.
Do I need to take action?
A light apple scab infection may be tolerated.
What if I do nothing?
A severe infection can make fruit unusable and weaken the tree. It should be treated.
Prevent Apple Scab
Signe Danler, Oregon State University
Plant Scab-resistant Apple and Crabapple Varieties
Resistant varieties include 'Akane' (Tokyo Rose), 'Chehalis', ’Enterprise’, ‘Freedom’, 'Liberty', 'Paulared', 'Prima', or 'Tydeman Red'.
"Apple Tree" by Hafsa Nabeel is licensed under CC BY-NC-ND 2.0.
Reduce Moisture on Foliage
Use sprinkler heads that do not wet the foliage of the tree, or use drip irrigation. Or, irrigate early in the day. This gives leaves time to dry before warmer daytime temperatures encourage scab growth. Prune trees to increase air flow. This will reduce the amount of time foliage is wet from rain or dew.
Left: Defoliated crabapple tree photo used with permission from James Walla.
Right: T. Davis Sydnor, The Ohio State University, Bugwood.org
Apply Fungicide at the Correct Times to Prevent Apple Scab
Tree on the left was not treated with fungicide during a severe outbreak. Note the thin canopy and defoliation. The tree on the right is healthy.
Solutions for Apple Scab
Non-chemical Methods
- Encourage fallen leaves to decompose rapidly.
- Rake up and dispose of fallen leaves.
Chemical methods
- Fungicides effectively control apple scab when used according to label directions.
- They must be applied before plants develop disease symptoms to work.
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 Rake Leaves |
Effective |
Low risk |
Recommended |
B Speed Leaf Decomposition |
Effective |
Low risk |
Recommended |
C Control with Fungicides |
Effective |
Moderate risk |
Use if Necessary |
|
D If Using Fungicides, Protect Yourself & Minimize Risks
|
A
Rake Leaves
Non-Chemical Method
"Rake leaves onto tarp" by Joseph Steiner is licensed under CCO 1.0 public domain
Rake Leaves
Recommended
Rake and destroy infected leaves. This can limit the disease to tolerable levels.
| Does it work? | Effective |
| How much effort? | Moderate effort |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
B
Speed Leaf Decomposition
Non-Chemical Method
"Decaying Leaves" by Thomas Fitzgerald is licensed under CC BY-NC 2.0
Speed Leaf Decomposition
Recommended
In the fall, apply nitrogen (5% urea) and a adjuvant to speed decomposition of fallen leaves. Adjuvants include Organic Wet Betty (yucca extract) and 30% yeast extract.
Shredding the leaves also speeds decomposition. Apply dolomitic lime in fall, after leaf drop. This will increase soil pH and help reduce fungus spores next spring.
| Does it work? | Effective |
| How much effort? | Moderate effort |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
C
Control with Fungicides
Chemical Method: Use with caution
iStock
Control with Fungicides
Use if Necessary
Fungicide sprays are necessary if the weather is rainy, and leaves are likely to remain wet for 9 or more hours.
| Does it work? | Effective Fungicides effectively prevent apple scab when used according to label directions. |
| How much effort? | Moderate effort Apply fungicides early and thoroughly to protect new growth. |
| 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 | El uso de fungicidas conlleva cierto grado de riesgo. El riesgo más bajo se produce sin el uso de fungicidas. You may be exposed to a fungicide if you:
Follow directions closely to reduce risk. |
Some products are available for home use. A few are listed below. These active ingredients, used individually or in a mixture, are suggested chemical treatments to control apple scab. Look for these chemical names in the “Active Ingredients” section of product labels.
- Neem oil
- Sulfur
- Copper Fungicide
- Myclobutanil
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
- The critical period for scab control comes as the young buds are opening. It is very hard to control apple scab once plants develop disease symptoms.
- Apply fungicide just after the buds begin to open. Continue until the apples are 1/2 inch (1.27 cm) in diameter.
- Repeat at regular intervals until dry weather. Check for application timing on the label.
- Researchers recommend alternating different active ingredient groups. Local populations of apple scab 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 licensed 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. 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 correct personal protection equipment. The right gear often includes chemical-resistant gloves, safety glasses, a long-sleeve shirt, pants, socks, and shoes.
- 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 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.
APPLE SCAB REFERENCES
Apple Scab
PNW Pest Management Handbooks
Apple Scab (pdf)
Washington State University Extension Service
Apple: Scab
Washington State University Hortsense
Apple and Pear Scab
University of California IPM