Prevention and Control of Powdery Mildew

Understanding which plants are prone to powdery mildew and why others are resistant can help you make informed decisions about what to plant in your garden and how to manage those that are susceptible. By choosing resistant varieties and maintaining good cultural practices, you can minimize the impact of powdery mildew in your garden.

Prevention of Powdery Mildew

1. Choose Resistant Varieties: Select plant varieties that are resistant or less susceptible to powdery mildew.

2. Proper Spacing: Ensure adequate spacing between plants to improve air circulation, which helps to reduce humidity levels around the foliage.

3. Watering Practices:

   • Water plants at the base, avoiding overhead watering, which can increase humidity and promote mildew growth.

   • Water early in the day to allow moisture on the plants to dry before evening.

4. Soil Management:

   • Keep the area around plants clean and free of debris, as organic matter can harbor the fungus.

   • Use well-draining soil to avoid excess moisture, which can contribute to mildew growth.

5. Mulching: Apply mulch around the base of plants to retain soil moisture and prevent splashing of water onto the leaves, which can spread spores.

6. Regular Monitoring: Inspect plants regularly, especially during periods of warm, dry weather followed by high humidity. Early detection can help prevent the spread.

Removal of Powdery Mildew

1. Prune Affected Areas:

   • Remove and destroy infected leaves, stems, or flowers as soon as you notice them.

   • Dispose of the infected plant material in the trash, not in compost, to prevent spreading the spores.

2. Natural Remedies:

   • Milk Spray: Mix 1 part milk with 2 parts water and spray the affected plants. Milk has natural anti-fungal properties.

   • Baking Soda Solution: Mix 1 tablespoon of baking soda, 1 teaspoon of liquid soap, and 1 gallon of water. Spray this solution on affected plants to kill the mildew.

3. Fungicides:

   • Edible Plants: Apply an organic fungicide, such as neem oil or sulfur-based products. These are effective and safe for edible plants.When treating edible plants, especially those you will soon harvest, prioritize non-toxic, organic solutions like milk sprays, neem oil, or baking soda. Chemical fungicides should be used with caution, ensuring they are safe for food crops.

   • Ornamental Plants: While you can use the same organic methods, you have more flexibility with chemical treatments since there’s no concern about consumption. For severe cases, you may need to use a chemical fungicide, but ensure it’s labeled safe for the specific plants you're treating. However, still consider the environmental impact and safety, particularly if the ornamental plants are near edible gardens or frequented by pets or children.

4. Improve Air Circulation:

   • Thin out the foliage to allow better airflow around the plants, which can help reduce the humidity that powdery mildew thrives on.

   • Ensure plants are not overcrowded.

5. Maintain a Dry Environment:

   • Avoid watering in the evening to reduce the amount of time plants stay wet, as mildew thrives in humid, dark conditions.

   • Increase sunlight exposure if possible, as powdery mildew is less likely to thrive in direct sunlight.

Washing Off Powdery Mildew

If you want to preserve as many leaves as possible, you can gently wash off the powdery mildew from the least affected leaves instead of removing them entirely. Choose a time when the plants are not exposed to direct sunlight, such as early morning or late afternoon. This prevents the leaves from getting sunburned after washing.

1. Prepare a mild solution using one of the following options:

   • Water and Baking Soda Solution: Mix 1 tablespoon of baking soda with 1 gallon of water. This helps to neutralize the mildew and prevent further spread.

   • Water and Dish Soap Solution: Mix a few drops of mild liquid soap (not detergent) with 1 gallon of water. The soap helps break down the mildew and makes it easier to wash off.

   • Water and Milk Solution: Mix 1 part milk with 2 parts water. Milk has natural antifungal properties and is gentle on the leaves.

2. Washing the Leaves:

   • Dip a soft cloth, sponge, or spray bottle into the solution.

   • Gently wipe or spray the affected leaves, focusing on the areas with visible mildew. Be careful not to scrub too hard, as this can damage the leaves.

   • If using a spray, ensure you thoroughly cover the affected areas, allowing the solution to sit for a few minutes.

3. Rinsing:

   • After wiping or spraying, rinse the leaves with clean water to remove any residue from the solution.

   • You can use a gentle spray from a garden hose or a watering can to do this.

4. Drying:

   • Allow the leaves to air dry naturally. Make sure there is good airflow around the plants to speed up the drying process and prevent further mildew growth.

   • Avoid watering the plants from above until the leaves are completely dry.

5. Follow-Up Care:

   • Monitor the leaves over the next few days. If you notice any new mildew spots, you may need to repeat the washing process.

   • Ensure the plants are in an environment with good air circulation and proper sunlight to help prevent future mildew outbreaks.

Plants Prone to Powdery Mildew

Powdery mildew is a common fungal disease that affects a wide variety of plants. Some of the most susceptible plants include:

1. Vegetables:

   • Cucurbits: Cucumbers, pumpkins, squash, and zucchini.

   • Tomatoes: Especially in humid conditions.

   • Peppers: Both hot and sweet varieties.

   • Beans: Particularly pole beans.

2. Fruits:

   • Grapes: Both wine and table varieties are prone to powdery mildew.

   • Apples and Pears: Especially in humid climates.

   • Strawberries: Can be affected under certain conditions.

3. Ornamentals:

   • Roses: Very susceptible to powdery mildew, particularly in humid environments.

   • Lilacs: Often affected, especially in areas with poor air circulation.

   • Zinnias and Phlox: Commonly get powdery mildew in gardens.

   • Begonias: Susceptible in both outdoor and indoor environments.

4. Trees and Shrubs:

   • Dogwoods: Particularly in shady, damp areas.

   • Oaks: Some species are prone, especially in moist conditions.

   • Maples: Certain varieties can be affected.

5. Proper Care and Maintenance: Plants that are well-cared for, with proper watering, fertilization, and pruning, are generally more resilient to diseases, including powdery mildew. Healthy plants can often fend off or recover from infections more effectively than stressed or neglected ones.

“Grow Your Own Food” blog posts

See the full list of our Grow Your Own Food blog posts. Each post is assigned ”tags” which are under the post title. If you need a quick answer to a gardening question give us a call or send a text to our customer support team – support[at]deep-roots-project.org AND 708-655-5299.

Deep Roots online store

See our online store for details about prices, ordering and delivery of raised beds, planter boxes, microbe-rich compost, worm castings, leaf mulch and more. We don’t sell traditional soil, since we use 100% compost as our growing medium. Our online store has 2 sections – (1) raised beds and planter boxes and (2) compost, worm castings, fertilizer.

Please contact our customer support team before placing an order online so we can assist you with the details and answer your gardening questions. You can pay by credit card in the store or by check.

(708) 655-5299 and support[at]deep-roots-project.org

Please leave your cell phone number when you sign up for our eNewsletter, if you want text message announcements now and then. 

Donations help us provide organic kitchen gardening education to individuals, organizations, and entire communities. Thank you in advance for contributing to our community and for sharing our website and blog with friends and family.