How can I treat fungal infections on roses naturally?
Written by
Michael Sullivan
Reviewed by
Prof. Martin Thorne, Ph.D.Roses are susceptible to fungal infections, especially in humid weather conditions. Fungal infections such as black spot, powdery mildew, and rust can quickly weaken your roses' stems and leaves. There are natural methods that provide a safer alternative to chemical controls. These tactics curb the spread of disease while also protecting the pollinators in your garden. I personally use these methods in my own garden.
Potassium bicarbonate is an effective organic fungicide. Mix 1 tablespoon per gallon of water, and spray every 7 days during an outbreak. Potassium bicarbonate raises leaf pH levels, creating a more inhospitable environment for fungi. Potassium bicarbonate is particularly effective against powdery mildew.
Neem oil is a naturally occurring product that interrupts the life cycles of fungi. As soon as you notice any first signs or symptoms, apply neem oil as a foliar spray to both surfaces of the leaves. This plant-based oil also has knockdown efficacy against a myriad of pest pressures, including aphids. Reapplications can occur after moderate rainfall to maintain protection.
Baking soda solutions change leaf surface chemistry. Mix 1 teaspoon of baking soda into 1 quart of water, and add a drop of soap. This will inhibit spore germination for a limited time. It is most effective when used as a preventive measure in high-humidity conditions.
Sanitation Practices
- Remove infected leaves immediately and seal in bags
- Disinfect tools with alcohol between plants
- Clear fallen debris weekly to break disease cycles
Spray Preparation
- Use warm water to dissolve ingredients fully
- Add surfactant like castile soap for better adhesion
- Test on few leaves before full application
Safety Measures
- Wear gloves during mixing and application
- Avoid spraying when temperatures exceed 85°F
- Protect beneficial insects by spraying at dusk
Cultural practices increase the effectiveness of other treatments. Where possible, create some space under bush cover to improve airflow around the bushes. Apply water only to the soil level via drip irrigation or consider overhead irrigation, applying water in the morning to allow sunlight to help dry leaves quickly. Each of these practices will create less-than-ideal conditions for fungal growth.
Maintaining consistency is essential with organic treatments. Begin applications when the new buds break open in the spring, and keep applications coming through the fall, particularly if there is wet weather. Alternate between products to help prevent resistance to the organic treatments. Healthy roses will respond to the constant care.
Read the full article: 10 Common Rose Bush Diseases and Solutions
