Rose powdery mildew is caused by the fungus Podosphaera pannosa and is a disease of roses.
The visible white growth can affect the plant’s entire aerial sections, creating microscopic spores that spread the disease.
Rose powdery mildew appears more frequently than we’d like, especially in humid climates or damp environments.
If you suspect powdery mildew rose problems, consult our guide to learn more about the condition. By the end, you’ll have a much better understanding of rose powdery mildew and how to deal with it. (Read About the Different Types of Roses)
What Causes Powdery Mildew On Roses?
Rose powdery mildew is a fungal disease where it produces spores and is dispersed by the wind. If your rose bushes are infected with powdery mildew, you’ll spot white or gray powdery patches on buds, leaves, stems, and petals.
When the disease is mild, your rose’s growth is stunted, and young leaves are bent and deformed. Following this, flower posture is abnormal, and with this combination, they all affect the plant’s growth and appearance.
When the disease is serious, it causes early deciduous rose leaves, deformity, or incomplete flower buds. Further diseases cause rose branches to wither or die completely.
While the fungus Podosphaera pannosa is the root cause, roses are susceptible to damp conditions and poor air circulation. Luckily, there are a few things you can do to help combat this disease.
How Do You Get Rid of Powdery Mildew?
Before symptoms appear, apply a fungicide containing flutriafol. Fungicides that are listed as suitable for the control of rose powdery mildew are:
- Provanto Fungus Fighter Concentrate (fungicides tebuconazole)
- Fungus Clear Ultra (triticonazole)
- Provanto Fungus Fighter Plus & Toprose Fungus Control & Protect (tebuconazole with trifloxystrobin)
Any of these fungicides are suitable for treatment and can help stop white powdery substances on your roses.
Any fungicide can be sprayed once at intervals of 10 days and 2–3 times. If you don’t wish to use a chemical fungicide, you can choose more natural methods to treat susceptible plants that may have powdery mildew. (Learn How Much Sun Do Roses Need)
How Do You Get Rid of Powdery Mildew on Roses?
Rose powdery mildew grows in environments that offer moderate temperatures with high humidity in the late spring. You may discover a greenhouse is a perfect place to create these conditions and get powder mildew on roses.
To prevent powdery mildew, ventilate roses and increase light conditions in your gardening environments. If your plants or raise bushes are of a high density, it means they are at high risk of diseases, and the mold will start spreading to other close-by plants.
Roses mold appears in a moisture-rich environment. Here are some of the lesser-known ways to treat roses with powdery mildew throughout the growing season.
Baking Soda (sodium bicarbonate): Out of all the homemade, organic solutions for powdery mildew, this is among the more well-known. You should note, there are studies, which indicate baking soda alone isn’t effective. However, when combined with horticultural or dormant oil and liquid soap, it is far better, especially when applied in the early stages before an outbreak.
- Into a gallon of water:
- Mix one tablespoon of baking soda and one teaspoon of dormant oil
- Add one teaspoon of insecticidal or liquid soap (not detergent)
- Spray on your plants every, one to two weeks.
Potassium bicarbonate, which is like baking soda, has the advantage of eliminating powdery mildew once it’s encountered. Potassium bicarbonate is a contact fungicide and kills powdery mildew spores quickly.
Mouthwash: Gardeners have found that if mouthwash can kill the germs in your mouth, then fungal spores of powdery mildew won’t stand a chance. Generic, ethanol mouthwash may be highly effective at control. Tests of one part mouthwash to three parts water work well. Make sure when applying as mouthwash can affect new foliage.
Vinegar: Being like mouthwash, the acetic acid in the vinegar helps control powdery mildew. A mix of 2-3 tablespoons of apple cider vinegar and making sure it has 5% acetic acid. Mix with a gallon of water. While too much vinegar can burn your plants, higher concentrations over 5% are more effective.
You can carry out some non-chemical cultural methods to help eradicate powdery mildew that will deal with the full rose rather than targeting parts of the plant.
To do this, you need to manage the environment around any susceptible plants. Plant your roses in full sun and make sure they have good air circulation. Rose bushes are higher targets for these fungi to attack.
Manage humidity and leaf wetness are key, so make sure not to plant too densely. Give plenty of space between your plants and aim for an open environment that will increase air circulation and lower humidity levels. (Learn How to Get Rid of Blackspot on Roses Naturally)
Spread your plants, and central pruning of stems ensures you have great airflow through the entire plant. A bush type could require considerable thinning early in the season before any sign on a healthy plant.
Can Plants Recover from Powdery Mildew?
Conditions favoring the powdery mildew, roses include dry foliage, high humidity, moderate temperatures, and not enough light.
- Look for disease-resistant varieties
- Provide adequate air circulation by not crowding plants.
- Site plants so they will get sufficient light of six hours or more daily.
- Avoid over-fertilization as you’ll find new growth more susceptible. Apply a slow-release fertilizer to deliver controlled growth.
If you need to respond to a powdery mildew problem that has already developed, early detection will be the best way to control and help eradicate problems. Many retail products are effective at preventing the spread of the disease. However, they’re not an assurance existing issues will be resolved.
Most conventional treatments are designed for infection prevention and control and not infection elimination. Because of this, it’s vital to have a control program before powdery mildew appears.
Mildew may be treated as we have seen with fungicide products with the active ingredient “chlorothalonil”, as this is among the most used. While successful, it will leave a white milky film on the leaf surface.
Sulfur and Lime/Sulfur
Sulfur prevents the development or spread of disease spores when it contacts them. The solution enters the leaves more effectively if mixed with hydrated lime. Bordeaux mix is a common variant and contains copper sulfate and hydrated lime. One thing to note is these can burn plant tissue and are toxic to soil microorganisms.
A new treatment for the fight against powdery mildew is milk. Many gardeners or specialists are unsure why it is so effective, yet it’s believed the natural compounds in milk work to combat the disease. As an aside, it can help boost the plant’s immune system. A weekly dose of one part milk to two parts water is effective. (Read About Milky Spore Powder)
High humidity is among the favorable conditions for powdery mildew to take hold. However, water is its enemy as it washes off spores before they can take root. Caution when using this method as wet foliage can lead to many other plant diseases. Use early in the day, so it dries quickly.
You can find Neem Oil as an organic option for disease and pest control. It works as effective disease control and broad-spectrum natural insecticide, which is kinder to beneficial insects. To treat infected plants against powdery mildew, the results vary, and it may not be the best solution.