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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Apple and Pear Powdery Mildew
Podosphaera leucotricha
Updated Dec 17, 2024
Make a Positive Identification
- Powdery mildew is a fungus that causes white powdery growth on leaves, twigs, blossoms, and fruit.
- Young leaves are the most susceptible to infection. Leaves become curled and distorted.
- Watch for small gray or white felt-like patches of fungus on the undersides of leaves.
- Powdery mildew is favored by humid nights and warm days. In Oregon it begins in spring and early summer.
Species: Powdery Mildew
Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org
The infection may over-winter in a bud. Young leaves may show symptoms as soon as they begin to grow. They may show gray-white powdery growth, often on the underside. Leaves become curled and distorted.
Species: Powdery Mildew
Jay W. Pscheidt, Oregon State University
Flowers infected with powdery mildew develop white powdery coating. They are deformed, then turn brownish and shrivel up.
Species: Powdery Mildew
Jay W. Pscheidt, Oregon State University
Infected apples show a net-like pattern of lines, known as russeting (left). Fruit infection happens very early in the season. The fruit on the right shows the normal, healthy appearance for this variety. Russeting may also be caused by cool wet weather, frost, pesticides and viruses.
Species: Powdery Mildew
N.S. Luepschen, Bugwood.org
The white fungus leaves a russeted patch by summer. The russeted area expands as the fruits enlarge.
Apple and Pear Powdery Mildew Benefits
- Powdery mildew is a fungal plant disease that damages apple trees. It doesn’t have any benefit for people or the environment.
Apple and Pear Powdery Mildew Risks
- Previous year infections can overwinter in dormant buds.
- New growth is dwarfed and distorted, and fungus is ready to reproduce and spread.
- Leaves may drop and weaken the tree.
- Fruit infected shortly after bloom develop brown or weblike, russetted scars
Risk Card
Does it cause harm?
Adults & Children
None
Property
Low
Pets
None
Annoyance
Some
Environment
None
Action Optional
Take Action?
Powdery mildew interferes with the proper functioning of leaves. It reduces shoot growth and reduces fruit set.
Do I need to take action?
If a severe infection occurs every year, you should take steps to control it.
What if I do nothing?
A light powdery mildew infection may be tolerated. A severe infection can weaken the tree. It should be treated.
Prevent Powdery Mildew on Apples and Pears
"Fuji Apples" by shinya is licensed under CC BY-ND 2.0
Plant Resistant Apple and Pear Varieties
Powdery mildew resistant apples include 'Fuji', 'Golden Delicious', 'Red Delicious', and 'Delicious'. Also, ‘Enterprise’ and ‘Pristine’ are resistant to both powdery mildew and apple scab.
See Apple Cultivar Susceptibility table.
Powdery mildew resistant pears include ‘Bartlett’, ‘Bosc’, ‘Seckel’ and ‘Starkrimson’.
See Pear Cultivar Susceptibility table.
"Apple Tree" by mattjiggins is licensed under CC BY 2.0
Plant Apple and Pear Trees in Sunny Areas With Good Air Circulation.
- Avoid planting pears downwind of apples. Powdery mildew on apples may spread to pears.
Don’t Apply Excess Fertilizer
Excess Nitrogen fertilizer causes flushes of succulent new growth. This tender growth is more susceptible to powdery mildew.
HOW TO GET RID OF POWDERY MILDEW
Prevention
- Plant resistant apple and pear varieties.
- Plant trees in sunny areas with good air circulation.
- Avoid planting pears downwind of apples. Powdery mildew on apples may spread to pears.
- Don’t over-fertilize, to prevent lush growth that is prone to infection.
Non-chemical Methods
- Prune out and destroy badly infected shoots as they appear in spring. This is ineffective when the disease is severe.
Chemical Methods
- Fungicides may effectively prevent powdery mildew when used according to label directions.
- Fungicides 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 Prune out infected shoots |
Somewhat effective |
Low risk |
Recommended |
B Lengthy overhead watering |
Somewhat effective |
Low risk |
Recommended |
C Control with Fungicides |
Effective |
Moderate risk |
Use if Necessary |
|
D If Using Fungicides, Protect Yourself & Minimize Risks
|
A
Prune out infected shoots
Non-Chemical Method
"_MG_6855 Pruning and training young apple trees" by Apple and Pear Australia Ltd is licensed under CC BY 2.0.
Prune out infected shoots
Recommended
- For small infections, prune out and discard diseased tissue as soon as it appears.
- Look for infected shoots and buds as soon as growth is beginning and remove them.
- Infected shoots and buds have a thin layer of fuzzy white fungus. They are flattened or shriveled compared to normal buds.
- Pear powdery mildew has not been observed overwintering in buds.
| Does it work? | Somewhat effective Pruning infected shoots removes the fungus. It also removes the infection for the next season. |
| How much effort? | Moderate effort |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
B
Lengthy overhead watering
Non-Chemical Method
"Wet Apple" by clogette is licensed under CC BY-NC-ND 2.0.
Lengthy overhead watering
Recommended
Lengthy overhead sprinkling may reduce active powdery mildew infections. The presence of water reduces spore germination.
| Does it work? | Somewhat effective |
| How much effort? | Low 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
Fungicides may effectively prevent powdery mildew when used according to label directions. They are most effective if applied shortly before bud break in the spring.
| Does it work? | Effective Fungicides must be applied before plants develop disease symptoms to work. |
| How much effort? | Moderate effort |
| 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 and pear powdery mildew. Look for these chemical names in the “Active Ingredients” section of product labels.
- Bacillus amyloliquifaciens strain D747
- Sulfur
- Mineral oil
- Neem oil
- 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
- Proper timing of fungicide sprays is important for them to be effective against apple and pear powdery mildew.
- Fungicide products work best when applied before plant diseases get started.
- Start treatments early in spring when new growth appears. Repeat during wet weather through spring and summer.
- Check for application timing on the label. It is very hard to control powdery mildew once plants develop disease symptoms.
- Researchers recommend alternating products (by active ingredient). Local populations of apple and pear powdery mildew 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.
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 AND PEAR POWDERY MILDEW REFERENCES
Apple-Powdery Mildew
PNW Pest Management Handbooks
Pear-Powdery Mildew
PNW Pest Management Handbooks
Apple: Powdery Mildew
Washington State University Hortsense
Pear: Powdery Mildew
Washington State University Hortsense
Apple Cultivar Resistance
PNW Pest Management Handbooks
Pear Cultivar Resistance
PNW Pest Management Handbooks
Powdery Mildew on Fruits and Berries
University of California IPM
Managing Diseases and Insects in Home Orchards
Oregon State University Extension Service