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Organic Ways to Kill Powdery Mildew

Updated on April 6, 2016
Powdery mildew on grapes.
Powdery mildew on grapes. | Source
Plants most susceptible to powdery mildew
Lilacs
Cucumbers
Squash
Roses
Crab apples
Phlox

What is the Powdery Mildew on My Plants Leaves?

As a former landscaper, I have seen a lot of plant diseases. One of the easiest ones to recognize is powdery mildew; it looks just like its name. The mildew will form a white or gray powdery film on a plant's leaves, stems, and fruit.

Powdery mildew is a fungal disease caused by the many varieties of the fungi which belong to the order Erysiphales. The fungus thrives in warm, humid environs, and overwinters in the soil. It is spread by the wind, insects and water run-off.

According to the Arizona Cooperative Extension, "Unlike most fungi, spores germinate on the surface of plant parts without the presence of free water."

Where does powdery mildew start?

The mildew usually starts on a plants lower leaves, and if the fungus is not treated it will spread over the entire plant. When the leaves become severely covered with the fungus, photosynthesis will be affected and leaves will yellow and drop off. As a result, the plant may become so stressed it will not flower and/or fruit with any vigor.

Are all forms of the fungus the same?

There are many forms of powdery mildew, and each is species specific. Grapes will suffer from the powdery mildew that affects only grapes, roses suffer from rose powdery mildew, and so on.

Although all plants can get the fungus, certain species are more susceptible to it.

If your plant has a black sooty substance on its leaves, it may be sooty mold. You can find information on that here: What is the Black Soot on my Gardenias?

How Can I Prevent Powdery Mildew?

Preventing the spread and/or severity of powdery mildew is the most cost effective way of dealing with the fungus. Try the following tips if you are battling the fungus in your garden and flower beds.

Buy mildew resistant varieties

There are a large variety of hybrid plants that are resistant or tolerant to the growth of powdery mildew. The resistant plants will be less likely to develop the mildew. The tolerant plants will show fewer ill effects of an infestation of the fungi.

Do not crowd plants

Good air circulation ensures lower humidity levels, inhibiting the growth of powdery mildew. Crowded plants will also provide too much shade for the lower leaves, encouraging fungi growth.

Do not grow susceptible plants in the shade

Although powdery mildew prefers warmth, it does not tolerate high temperatures. Plants that are shaded much of the day will stay cooler, encouraging the growth of mildew.

Powdery mildew on poinsettia plant.
Powdery mildew on poinsettia plant. | Source

Dispose of infected leaves and stems

Never use the infected plant leaves or fruit as mulch. Trim off infected leaves and stems and dispose of properly. If your municipality allows backyard fires, then burn the debris. If not, dispose of the debris according to your local plant disposal regulations.

Water the soil, not the plants

While the water will not encourage mildew growth, splashing the leaves with water will spread the spores. Run a hose to the base of your plants instead of using a sprinkler system.



Potassium Bicarbonate Organic Fungicide

What are the Organic Treatments for Killing Powdery Mildew?

When treating your plants, make sure the leaves are coated with the solution. Reapply weekly unless otherwise specified on a products label.

Milk

Numerous studies have shown milk and/or whey to be an effective anti-fungicide. The milk and whey are believed to produce free radicals which are toxic to the fungus.

Mix 60 parts water with 40 parts milk or whey and spray onto the affected plants bi-weekly.

or

Mix one oz powdered milk to 2 liters of water.

Baking soda

Baking soda changes the pH of the fungus and kills it.

Mix 1 tbs of baking soda and 1/2 tsp liquid hand soap with one gallon of water.

Spray solution on affected leaves, and dispose of any remaining solution. Do not apply during daylight hours. It may be best to test one or two leaves to see if the solution will cause the plant to suffer sunburn.

Potassium bicarbonate

Potassium bicarbonate is a safe, effective fungicide. It is used as a leavening agent, and is used in wines and bottled waters.

Mix 3 tbs potassium bicarbonate, 3 tbs vegetable oil and a half teaspoon soap iinto a gallon of water.

Sulfur

Sulfur is a natural product that is very effective at preventing and controlling powdery mildew. Sulfur can be bought as a dust, or as a liquid which can be added to sulfur vaporizers.

Follow the dosing instructions closely and wear gloves, eye protection, and a face mask. Avoid inhaling or coming into contact with the sulfur .

Neem oil

Neem oil is made from the seeds and fruit of the evergreen neem tree. Neem oil works by disrupting the plants metabolism and stopping spore production.

Mix 3 tbs of neem oil to one gallon of water.

Take precautions to avoid sunburn of leaves, and avoid spraying the plant's buds and flowers.

Copper fungicides

Copper is a very effective fungicide, but it is very important to follow label directions closely. Too much copper will be detrimental to the plant and the soil.

Powdery mildew on pumpkin leaves,
Powdery mildew on pumpkin leaves, | Source

Vinegar

Vinegar is very acidic. When sprayed on powdery mildew it changes the fungi's pH, effectively killing it.

Mix 4 tbs of vinegar with 1 gallon of water. Reapply every three days.

Garlic

Garlic has a high sulfur content and is an effective anti-fungicide. Garlic oil can be bought commercially if you do not wish to make the solution at home. Garlic works best when added to organic oil mixtures.

Crush six cloves and add to one ounce of an organic oil such as neem oil and one ounce of rubbing alcohol. Let set for two days, then strain and retain the liquid and crushed garlic. Again soak the garlic, this time in one cup of water for a day. Strain out and dispose of the crushed garlic. Add the oil and alcohol mixture and garlic water to one gallon of water. Spray your plants, coating only the leaves.


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    • profile image

      Jasmine Flower 8 days ago

      That is a really good idea John.

    • profile image

      John 2 months ago

      Try "mitey sauce" a local company- the coconut oil in it works on Powdery mildew but does not block the stomata like neem oil does.

    • Gcrhoads64 profile image
      Author

      Gable Rhoads 2 months ago from North Dakota

      Liz, according to this website, the rosemary is safe to eat: https://extension.umd.edu/growit/downy-mildew-basi...

      Other sites say it may affect the flavor. If you are treating the plants, wash the leaves thoroughly.

    • profile image

      Liz 2 months ago

      I have some on my rosemary plant, what happens if I eat it?

    • profile image

      Carmine 2 months ago

      I think if powdery mildew on grapes turns the skin dark color and some skins crack it is too late those clusters should be cut off and discarded i trash bin. Then the infected vines should be sprayed with one of the articles recommended materials

    • profile image

      Vishal 5 months ago

      In India Maharashtra the powdery mildew have largely affected grapes...

    • profile image

      Mike 14 months ago

      Fist site I found that gave the when to reapply info. Thanks.

    • Gcrhoads64 profile image
      Author

      Gable Rhoads 20 months ago from North Dakota

      Thanks for the comments Kristen and breathing. It is encouraging to get positive feedback. :)

    • breathing profile image

      Sajib 20 months ago from Bangladesh

      Plant lovers will be greatly benefited from this post. Indeed plants are subjected to many diseases. Powdery mildew is a very common disease among the plants. Many people who have their own plants don’t know how to treat powdery mildew. This post can be the cornerstone for them. The steps described in this hub are really worthwhile. I’ve tried a few ones myself and find them to be really effective. The organic ways are very much helpful. That’s why I advise the plant lovers to use the teachings of this post to exterminate powdery mildew. Also none of the processes are costly.

    • Kristen Howe profile image

      Kristen Howe 24 months ago from Northeast Ohio

      Great hub, Gable. This is so useful to know for next season, when I watch over my container garden. I'll keep it in mind to use milk or baking soda, if I do have that powdery mildew on my plants. Two green thumbs up!

    • profile image

      JANARDHAN N 3 years ago

      this as given me some assistance to fight against powdery mildew

      thanks to rentokil

    • Gcrhoads64 profile image
      Author

      Gable Rhoads 4 years ago from North Dakota

      I'm glad I could help. :)

    • RTalloni profile image

      RTalloni 4 years ago from the short journey

      Thanks for this helpful look at eliminating powdery mildew from plants. I have one that needs attention…