Squash plant with powdery mildew
Organic Gardening

Powdery Mildew: What is it and How to Get Rid of It

At certain times of the growing season, you may notice a white, powdery substance on your plants. This is powdery mildew. What is it and how can you keep it under control? Check out this post for identification, preventative measures and plant care.

Powdery mildew on squash: Squash plant with powdery mildew

Powdery Mildew in the Garden

At certain times during the growing season, you may notice a white, powdery substance on your plants. This is powdery mildew. 

What is it though and how can you keep it under control?

Powdery mildew is a very common occurrence in the garden and it’s hard to keep it under control in all honesty. One day your plants are looking healthy and green, but within a few weeks into the growing season, you see this powdery residue on them.

What is Powdery Mildew and How Do You Identify It?

Powdery mildew is one of the most common occurrences in the garden. It’s a fungal disease and easily identified by gray and white powdery spots on the leaves. It quickly spreads until the whole leaf is covered. Eventually, all the leaves will be covered with powdery mildew. If you’re wondering what it looks like, imagine spreading baby powder on your plant’s leaves. Powdery mildew can affect many different plants. It affects vegetables, ornamental plants, fruit trees, shrubs, and forest trees. However, the most commonly affected plants are cucurbits, nightshade, and legumes. 

In my garden, powdery mildew is an issue with all of my squash plants. My zucchini, pumpkin, and spaghetti squash plants without fail all get powdery mildew at some point during the summer. I have not had it affect my eggplants (nightshade) or my peas and beans, thankfully.

How Does Powdery Mildew Spread?

There are a few different ways that powdery mildew can spread in your garden or to your garden.

  1. Wind: Powdery mildew can be spread by the wind. The wind can carry the spores which can travel far.

  2. Contaminated Soil: If you’ve had the fungus in your garden before though, dormant spores can become reactivated given the right conditions. The spores lay dormant in old vegetative material and weeds. 

  3. Weather: Powdery mildew loves warm, dry climates, but does also like a fair amount of humidity.

  4. Poor air circulation and not enough sunlight are the perfect storm for this type of fungus. It’s rarely fatal to the plant. However, it can cause damage. It does not allow the plant to properly absorb nutrients and water. Although the leaves eventually wither and yellow on the plant, the plant can still produce fruit in most instances.

Preventative Measures and Care for Powdery Mildew

Although it’s difficult to prevent an invasion of spores, there are some preventative measures you can take.

Steps to Prevent Powdery Mildew

Although there is no guarantee that powdery mildew won’t appear in your garden, here are some steps you can take to try to prevent it.

  • Air circulation: Air circulation is an overall important. It helps to prevent a lot of diseases from your plants and allows plants to properly dry out any accumulated moisture and humidity.

  • Powdery mildew resistant varieties: select varieties of plants that are powdery mildew resistant. An example of a resistant zucchini variety is dunja. Not only is dunja resistant to powdery mildew, but it’s an excellent performer in high heat. It’s also resistant to Watermelon Mosaic Virus, Papaya Ringspot Virus, and Zucchini Yellow Mosaic Virus.

  • Finding the right spot for your garden is a crucial step. Be sure to set up your garden in a really sunny spot rather than in shade. Most plants in the garden need 8+ hours of sunlight to thrive and grow fruit.

  • Water at the base of the plant as opposed to overhead. Watering from overhead causes splashing of the spores onto the plants. However, it is not a very reliable preventative measure since that rain can cause splatter.

  • Consider vertical gardening for plants like squash. Growing vertically helps reduce pests and disease from spreading.

  • Keep plants nice and tidy.

    This goes hand-in-hand with proper air circulation. By keeping your plants well trimmed and tidy, it helps promote good air circulation. For plants like tomatoes, peppers, and eggplants, trim off any low hanging branches or ones that come in contact with the ground. By keeping branches off of the ground it reduces splatter of water from the ground onto the plant where diseases may be, and helps to reduce pests. Fruit does not have the opportunity to lay on the ground thereby reducing pests.

Care for Powdery Mildew: 5 Homemade Recipes

Once you have powdery mildew, it’ll be very hard to get under control. It spreads very rapidly from leaf to leaf and from plant to plant. There are homemade remedies for preventative measures. Although there are chemical fungicides that can handle powdery mildew very well, I only use organic or natural methods in my garden. Even if you wash your produce very well, residue from what was sprayed on it remains on the produce and can be absorbed.

Note: Only apply treatments either early in the morning or in the evening. Do not treat plants during the heat of the day as it can lead to scalding of the plant.

Baking Soda

A solution of baking soda is an effective treatment for powdery mildew. Mix 1 teaspoon of baking soda with 1 quart of water and thoroughly spray down the plant.

Diluted Milk

It’s not clear why milk is effective, but it gets the job done! Dilute milk with water (1:10) and thoroughly spray down the plant. 

2 bottles of milk in a bowl of ice
Diluted Milk Recipe

Apple Cider Vinegar (ACV) Mix

Vinegar is a great tool for fighting powdery mildew. A natural occurring chemical called acetic acid is present in vinegar. It’s important to use the right type of vinegar since vinegars that are too high in acetic acid can burn plants. Apple cider vinegar contains 5% acetic acid.

Recipe: Mix 2 to 3 tablespoons of ACV in 1 gallon of water.

Bottle of apple cider vinegar
Bottle of apple cider vinegar

Potassium Bicarbonate

Potassium bicarbonate works similar to baking soda. It kills the mildew and spores on contact.

Recipe: Mix 1 tablespoon of potassium bicarbonate, 1 tablespoon of vegetable oil, ½ teaspoon of Castile soap, and 1 gallon of water. Spray on plants by saturating both sides of the leaves.

Neem Oil

Neem oil is a natural occurring pesticide made from neem seeds. Follow the instructions provided on the bottle for the appropriate amount for application.

Care after Powdery Mildew

After you’ve had powdery mildew in your garden, it’s important to decontaminate the area. Remove all infected foliage and either throw it out or burn it. Do not compost! Composting will not destroy the spores and will continue the vicious cycle. If you’ve pruned plants that have powdery mildew, thoroughly clean tools with rubbing alcohol.

Looking for other tips on plant care? You may be interested in the following posts:

Blossom End Rot: What is it and How to Prevent it

My Tomato Plant Leaves Look Grey/Purple: What is the Cause?

Tomato Blight: What is it, What Varieties are Resistant, and How to Prevent Blight

How to Troubleshoot Pepper Plant Growing Problems

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