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Rose Downy Mildew

Peronospora sparsa

Updated Apr 11, 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

Rose foliage with purplish, angular spots

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

Rose downy mildew spore mass on the underside of leaf

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.

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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.

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.

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.

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
D PREVENT ROSE DOWNY MILDEW

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

Gloved hand pulling infected leaves from rose bush

Signe Danler, Oregon State University

Remove stems, leaves, and flowers that show disease. This reduces spread of the disease.

Raking diseased leaves into bag for disposal

Signe Danler, Oregon State University

Rake up and remove diseased leaves that fall to the ground.

Weston Miller, Oregon State University

Dispose of diseased material in your debris bin, compost pile, or burn pile. Don’t use homemade compost that includes diseased rose material to amend the soil near your rose bushes.

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	Using fungicides includes some amount of risk. The lowest risk comes without using fungicides. You may be exposed to a fungicide if you: Get it on your skin Breathe it in Eat or smoke afterward without washing hands Touch or eat plants that are wet with spray (you, pets, or children) Bring it inside on your shoes or clothes 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.

Example label with active ingredient neem oil

PICOL

Sample product label with Active Ingredient(s) highlighted

A red box on the example label highlights active ingredient Clarified hydrophobic extract of Neem oil.

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

Gloved hands holding fungicide package to read label

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.
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).