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Pest SolutionsPESTS + WEEDSUSING PESTICIDES OR HERBICIDES?
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Rose Downy Mildew
Peronospora sparsa
Updated Oct 10, 2024
Make a Positive Identification
- Downy mildew causes purplish to dark-brown, irregular spots on leaves, stems & flowers.
- The spots become angular as they enlarge and stop growing at major leaf veins.
- Pale, felty spore masses form on the underside of leaves.
- Infected leaves turn yellow and drop from the plant earlier than healthy leaves.
Species: Downy mildew
Melodie Putnam, Oregon State University
Look for irregular, purplish spots that may stop at leaf veins. Leaves may turn yellow.
Species: Downy mildew
Penn State Department of Plant Pathology & Environmental Microbiology Archives, Penn State University, Bugwood.org
Purplish blotches caused by rose downy mildew on rose cane.
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.
LOOK-ALIKES: BLACK SPOT AND POWDERY MILDEW
Species: Black spot
William Fountain, University of Kentucky, Bugwood.org
Rose black spot is a fungal disease. It causes black spots and blotches with diffuse edges on rose leaves. See How to Get Rid of Rose Black Spot
Species: Powdery mildew
Dr Parthasarathy Seethapathy, Tamil Nadu Agricultural University, Bugwood.org
Powdery mildew is also a fungal leaf disease. It causes powdery white areas on both the upper and lower sides of the leaves. See How to Get Rid of Rose Powdery Mildew
Rose Downy Mildew Benefits
Downy mildew is a plant disease that harms susceptible rose plants. It doesn’t have any benefit for people or the environment.
Rose Downy Mildew Risks
- Downy mildew causes damage to leaves, stems, and flowers.
- Rose bushes fail to thrive. Canes may die back.
- Downy mildew can cause most leaves to fall off rose shrubs.
Risk Card
Does it cause harm?
Adults & Children
None
Property
Low
Pets
None
Annoyance
Some
Environment
None
Action Optional
TAKE ACTION?
Rose downy mildew weakens plants. If you don’t like how it looks, you will need to take action.
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 downy mildew weakens plants. It can cause cane dieback and leaf loss.
PREVENT ROSE DOWNY MILDEW
"20090616_PortlandRoseGarden_JustJoey_Cutler_5240" by Wendy Cutler is licensed under CC BY 2.0.
Plant Resistant Rose Varieties
- Rose varieties that resist other diseases are also likely to resist downy mildew. Disease resistant rose varieties include ‘Carefree Spirit', ‘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).
- Disease resistant varieties may be available at nurseries and garden centers. Look on the plant tag or ask a store employee.
rcmirani, iStock
Don’t bring diseased roses into your garden
- Inspect new rose shrubs for signs of disease before buying.
Signe Danler, Oregon State University
Prune roses to promote airflow
- Thin out and space canes to open up the center of the shrub. This helps the leaves dry quickly after rain to reduce disease pressure.
- Avoid overhead watering.
- 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 DOWNY MILDEW
Prevention
- Plant resistant rose varieties for new plantings of roses. Rose varieties that resist other diseases are also likely to resist downy mildew. 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 rose downy mildew disease symptoms. Watering at this time allows the leaves to dry. However, don’t overhead water if other rose diseases are present.
Non-chemical Methods
- Remove stems, leaves, & flowers showing disease. Rake up diseased leaves.
- Prune established rose plantings to maximize airflow.
Chemical Methods
- Fungicides are pesticides that target fungal diseases on plants. Check for application timing on the label.
- Control of rose downy mildew with fungicides is difficult. Non-chemical control is more likely to be effective.
- It may be hard to control rose downy mildew once plants develop disease symptoms. Use fungicides according to the label instructions.
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 Control with Fungicides |
Somewhat effective |
Moderate risk |
Use if Necessary |
|
C 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 downy mildew disease life 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
Control with Fungicides
Chemical Method: Use with caution
iStock
Control with Fungicides
Use if Necessary
| Does it work? | Somewhat effective Control of rose downy mildew with fungicides is difficult. Fungicides must be applied before plants develop disease symptoms to work. Non-chemical control is more likely to be effective. |
| 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 downy mildew. Look for these chemical names in the “Active Ingredients” section of product labels. Look for product labels that state the product is effective for rose downy mildew.
- Neem oil Clarified hydrophobic extract (Some formulations are OMRI-listed for organic use.)
- Sulfur
- Bacillus amyloliquifaciens strain D747
- Copper fungicides
- Chlorothalonil
- Captan
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 downy mildewt.
- Check for application timing on the label. It may be hard to control rose downy mildew once plants develop disease symptoms.
- Ensure thorough coverage of leaves of your spray applications. Cover the undersides of leaves.
- Researchers recommend alternating products (by active ingredient). Local populations of rose downy 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 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 DOWNY MILDEW REFERENCES
Rose (Rosa spp.) and hybrids: Downy Mildew
PNW Pest Management Handbooks
Controlling Diseases and Aphids on Your Roses
OSU Extension Service Publication EC 1520
Roses: Diseases and Abiotic Disorders
University of California IPM
Downy Mildew of Roses
University of California IPM
Rose: Downy Mildew Fact Sheet
Washington State University Extension