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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Rose Powdery Mildew
Podosphaera (previously Sphaerotheca) pannosa var. rosae
Updated Oct 10, 2024
Make a Positive Identification
- Powdery mildew causes white powdery growth on rose bush leaves and flower buds.
- Infected leaves may be distorted. They may die and drop from the plant earlier than healthy leaves.
Species: Powdery mildew
Dr Parthasarathy Seethapathy, Tamil Nadu Agricultural University, Bugwood.org
Look for white spots forming on young leaves, buds, & stems in the spring.
Species: POowdery mildew
Dr Parthasarathy Seethapathy, Tamil Nadu Agricultural University, Bugwood.org
Leaves and shoots are twisted or distorted. New growth is often impacted.
LOOK-ALIKE: DOWNY MILDEW
Species: Downy mildew
Jean L. Williams-Woodward, University of Georgia, Bugwood.org
Downy mildew is a fungal leaf disease. It causes purple spots on the upper leaf surface. See How to Get Rid of Rose Downy Mildew
Species: Downy mildew
Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org
Pale, felty spore masses form on the underside of leaves. They don’t form on the upper side of leaves. By comparison, powdery mildew forms on the upper and lower surfaces of leaves.
Rose Powdery Mildew Benefits
Powdery mildew is a plant disease that harms susceptible rose plants. It doesn’t have any benefit for people or the environment.
Rose Powdery Mildew Risks
- Powdery mildew causes damage to leaves, stems, and flowers.
- It can cause leaves to fall off rose shrubs.
- Rose bushes fail to thrive.
Risk Card
Does it cause harm?
Adults & Children
None
Property
Low
Pets
None
Annoyance
Some
Environment
None
Action Optional
TAKE ACTION?
Rose powdery mildew weakens plants.Take action if you can’t tolerate the damage.
Do I need to take action?
If you don’t like how it looks, you will need to take action.
What if I do nothing?
Rose powdery mildew weakens plants.
PREVENT ROSE POWDERY MILDEW
"20090616_PortlandRoseGarden_JustJoey_Cutler_5240" by Wendy Cutler is licensed under CC BY 2.0.
Plant Resistant Rose Varieties
- Powdery mildew resistant rose varieties include ‘Electron’, ‘Just Joey’, ‘Tournament of Roses’, ‘Europeana’ and ‘Showbiz’, climber ‘Dublin Bay’, and Rosa rugosa varieties.
- For more varieties, See Rose Cultivar Resistance (PNW Plant Disease Management Handbook).
rcmirani, iStock
Don’t bring diseased roses into your garden
- Inspect new rose shrubs for signs of disease before buying.
- When planting rose bushes leave enough space between plants to ensure good airflow.
- Prune established rose bushes to maximize airflow.
- Plant roses in full sun.
HOW TO GET RID OF ROSE POWDERY MILDEW
Prevention
- For new rose plantings, choose varieties that are resistant to powdery mildew and other diseases. See Rose Cultivar Resistance (PNW Plant Disease Management Handbook).
- Don’t bring diseased roses into your garden.
- When planting rose bushes leave enough space between plants to ensure good airflow. Plant in full sun.
- Overhead watering during midday may limit the disease. Don’t overhead water if other rose diseases are present.
Non-chemical Methods
- Remove stems, leaves, & flowers showing disease. Rake up fallen leaves.
- Prune established rose plantings to maximize airflow.
Chemical Methods
- Fungicides effectively control powdery mildew when used according to the label instructions. Fungicides are pesticides that target fungal diseases on plants.
- Check for application timing on the label. It may be hard to control powdery mildew once plants develop disease symptoms.
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 Sanitation: Pruning and Raking Leaves |
Effective |
Low risk |
Recommended |
B Water Spray |
Somewhat effective |
Low risk |
Recommended |
C Control with Fungicides |
Effective |
Moderate risk |
Use if Necessary |
|
D If Using Fungicides, Protect Yourself & Minimize Risks
|
A
Sanitation: Pruning and Raking Leaves
Non-Chemical Method
"cobwebs" by anjollie123456 is licensed under CC BY-NC-ND 2.0
Sanitation: Pruning and Raking Leaves
Recommended
Raking fallen leaves and pruning to promote airflow disrupts the rose powdery mildew disease cycle.
| Does it work? | Effective These non-chemical strategies help minimize rose disease problems. |
| How much effort? | Moderate effort |
| What's the risk? | Low risk |
| Possible risk of exposure or harm from chemicals | NONE |
Signe Danler, Oregon State University
Signe Danler, Oregon State University
Weston Miller, Oregon State University
B
Water Spray
Non-Chemical Method
ronstick, stock.adobe.com
Water Spray
Recommended
Use a high pressure water spray on infested stems and buds. Use a strong spray 2-3 times per week to knock back powdery mildew.
| Does it work? | Somewhat effective This method will knock back powdery mildew but won’t get rid of it. |
| 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
| Does it work? | Effective Fungicides effectively prevent rose powdery mildew when used according to label directions. |
| How much effort? | Moderate effort |
| What's the risk? | Moderate risk |
| 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 are suggested chemical treatments to control rose powdery mildew. Look for these chemical names in the “Active Ingredients” section of product labels.
- Bacillus amyloliquifaciens strain D747
- Mineral oil
- Neem oil Clarified hydrophobic extract (Some formulations are OMRI-listed for organic use.)
- Sulfur
- Copper fungicides
- Chlorothalonil
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 rose powdery mildew.
- Check for application timing on the label. It may be hard to control rose powdery mildew once plants develop disease symptoms.
- Researchers recommend alternating products (by active ingredient). Local populations of rose 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.
SEE OTHER COMMON PACIFIC NORTHWEST ROSE PROBLEMS
Content provided by editor Weston Miller and writers Signe Danler and Jeremiah Mann. Pesticide safety information edited by Kaci Buhl.
Peer review facilitated by OSU Department of Horticulture.
ROSE POWDERY MILDEW REFERENCES
Rose (Rosa spp.) and hybrids-Powdery Mildew
PNW Pest Management Handbooks
Controlling Diseases and Aphids on Your Roses
OSU Extension Service Publication EC 1520
Rose Cultivar Resistance
PNW Pest Management Handbooks
Powdery Mildew on Ornamentals
University of California IPM