Sasha CampbellPowdery mildew can spread quickly through a garden. Once it appears, it can weaken plants, slow their growth, and reduce harvests if left untreated [1].
Several homemade and natural sprays may help prevent, slow, or control this common plant disease. Some use household ingredients, while others are ready-made garden products.
Many of these options are inexpensive. However, even natural treatments can damage plants if they are too strong or used incorrectly.
Identification
Powdery mildew is a group of fungal diseases. It causes white or gray powdery spots on leaves, stems, flowers, and sometimes fruit [2, 3].
It often grows well during warm days, cool nights, and humid weather. Crowded plants and poor airflow can make it worse. Unlike many fungal diseases, powdery mildew does not need wet leaves to infect a plant.
Many different fungi cause powdery mildew. The type that attacks one plant may not be able to infect another kind of plant.
Powdery mildew can affect vegetables such as cucumbers, squash, tomatoes, zucchini, beans, and peppers. It may also appear on apples, grapes, pears, and strawberries.
Ornamental plants such as roses, zinnias, bee balm, peonies, and some succulents can also develop the disease.
The Best Sprays for Powdery Mildew
These sprays may help prevent, slow, or control powdery mildew. Their effectiveness varies, and some work better as preventive treatments.
Always test a spray on one or two leaves first. Wait at least 24 hours to check for damage before treating the entire plant. Spray during the cool part of the day, not in strong sunlight or extreme heat.
Remove badly infected leaves if the plant still has plenty of healthy growth. Do not remove too many leaves at once because this can weaken the plant. Place infected material in the trash.
1. Baking Soda Spray
Baking soda spray may help prevent powdery mildew or slow its spread. It works best when used as soon as the first white spots appear.
To make the spray, mix one tablespoon of baking soda with one gallon of water. Add one teaspoon of mild liquid soap to help the mixture cover the leaves.
Spray the affected areas lightly. Do not use the mixture too often or allow large amounts to run into the soil. Baking soda contains sodium, which can build up in the soil and harm plants.
A small amount of mild soap is sometimes added to homemade sprays to help them cover leaves. Soap alone is not a dependable treatment for powdery mildew.
Avoid detergents, degreasers, and products containing bleach or strong fragrances. These ingredients may burn plant leaves.
2. Milk Spray
Milk spray may help control powdery mildew on certain plants, including squash [4].
To make a milk spray for powdery mildew, mix one part milk with nine parts water.
Shake the mixture and spray it onto both sides of the leaves. Reapply it every 7 to 14 days if needed.
Milk may leave a light residue or sour smell on plants. Test it on a small area before spraying the whole plant.
3. Apple Cider Vinegar Spray
Apple cider vinegar is sometimes suggested as a home remedy for powdery mildew. However, there is little research showing that it works, and even diluted vinegar may burn plant leaves.
If you want to try it, mix one tablespoon of apple cider vinegar with one gallon of water. Spray one or two leaves first and wait at least 24 hours.
Stop using the spray if the plant develops brown spots, curled leaves, or other signs of damage. Do not make the mixture stronger, as this increases the risk of leaf burn.
4. Neem Oil Spray
Neem oil has fungicidal and insecticidal properties. It may help control mild to moderate powdery mildew infections.
Neem products come in different strengths. Mix and apply the product according to the label, rather than using one recipe for every brand.
Cover the affected leaves thoroughly, including their undersides. Do not use neem oil on dry, wilted plants or during hot weather. Avoid spraying open flowers or applying it while bees are active.
Do not use neem oil close to a sulfur treatment. Read both product labels to learn how long you must wait between treatments.
5. Potassium Bicarbonate Spray
Potassium bicarbonate is one of the more effective treatments for powdery mildew. It can make the leaf surface less suitable for the fungus.
It is best to buy a potassium bicarbonate product made for plants. Follow its label for mixing and application instructions.
Although potassium bicarbonate is similar to baking soda, it does not add sodium to the soil. However, a strong mixture can still damage leaves.
6. Sulfur Spray
Sulfur has been used to manage powdery mildew for many years [5]. It works best as a preventive treatment or when the disease is first developing.
Purchase a wettable sulfur product labeled for the plant you want to treat. Mix and apply it according to the product directions.
Do not apply sulfur during hot weather. It can also damage certain squash, melon, berry, and ornamental varieties.
Do not apply sulfur close to an oil treatment, including neem, jojoba, or horticultural oil. Check both labels for the required waiting period.
Wear the protective clothing listed on the label. Avoid breathing sulfur mist or dust.
7. Horticultural Oil Spray
Horticultural oil can help control mild to moderate powdery mildew infections. It can suppress the fungus when it thoroughly covers the affected parts of the plant [6].
Choose a horticultural oil labeled for powdery mildew and the plant you are treating. Follow the label for mixing and spraying.
Cover the leaves well, but do not spray dry, wilted, or water-stressed plants. Avoid using the oil during very hot weather.
Do not use horticultural oil within the waiting period listed for a sulfur treatment. Using oil and sulfur too close together can badly burn plants.
8. Jojoba Oil Spray
Jojoba oil is a plant-based oil found in some garden fungicide products. It may help reduce mild to moderate powdery mildew infections [6].
Do not make a garden spray with cosmetic jojoba oil. Instead, choose a product labeled for treating powdery mildew on plants and follow its directions.
Test the product on a small area first. Do not spray during hot weather or on dry, wilted plants. Keep it away from sulfur treatments for the amount of time given on the product labels.
9. Bacillus-Based Biofungicide
Some biological fungicides contain helpful bacteria such as Bacillus subtilis or Bacillus amyloliquefaciens. These bacteria can help stop powdery mildew from infecting new plant growth.
Biofungicides usually work best as preventive treatments or during the earliest stage of an infection. They may not control an established outbreak as well as horticultural oil or sulfur [7].
Arber Bio Fungicide is one example of a product containing Bacillus amyloliquefaciens. Other brands are also available.
Choose a product labeled for powdery mildew and the plant you are treating. Follow the label carefully because mixing and application directions vary by product.
How to Prevent Powdery Mildew
- Give plants enough space so air can move between them.
- Grow resistant plant varieties when possible.
- Place plants where they will receive the right amount of sunlight.
- Avoid giving plants too much nitrogen fertilizer [1].
- Remove badly infected plant parts without taking off too many leaves.
- Clean up infected plant debris at the end of the growing season.
- Keep plants properly watered because stressed plants may suffer more damage.
- Check both sides of the leaves often so you can begin treatment early.
Takeaway
Homemade and natural sprays may help slow powdery mildew, especially when you begin treatment after noticing the first white spots.
Choose one treatment that is safe for your plant. Do not combine different sprays unless their labels say it is safe.
Do not apply sulfur and oil sprays close together. Follow both labels for the required waiting period because using them too close together can severely burn plants.
A badly infected plant may not recover fully. However, early treatment can help protect its healthy leaves and new growth.
Thank you. Very helpful and informative article