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Preventing Powdery Mildew Damage in the Garden

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Powdery mildew is a common disease in the garden. The fungi has a number of varieties and can impact a wide range of vegetable crops. There are a number of natural tactics gardeners can take to reduce the risk of damage from this garden pest.

Dealing with a different kind of pest? Check out some of these natural solutions.

powdery mildew on squash plant

Powdery mildew requires living plant material on which to grow. It won’t take up residence anywhere else.

In my garden, cucurbits — squash and cucumbers — are especially vulnerable, as are tomato plants. But powdery mildew can attack a large number of vegetable crops. Artichokes, beans, carrots, eggplant, melons, peas, peppers; all can fall victim to these fungi. Landscape plants, too, can be damaged by this mildew.

Powdery mildew: Signs to watch for

The first sign of powdery mildew is often telltale white spots on leaves. Looking somewhat dry and powdery, these spots eventually spread and cover a large area of the leaf. You may also see damage on plant stalks. Infected leaves may turn yellow, wither, and eventually fall off.

close up of fungus on leaf

Prevention in the home garden

As with most garden problems, prevention is the best course of action. There are several tactics gardeners can take to naturally keep powdery mildew at bay.

1. Choose vegetable varieties that are resistant to powdery mildew. You can find both heirloom and hybrid plant varieties that fit this bill.

2. Plant your garden in a sunny location. Fungal growth is inhibited by extreme heat and direct sunlight. If you’re limited on sun and growing a shade garden, be vigilant about watching for signs of this pest.

3. Allow for plenty of air circulation between plants.

4. Spray neem oil — a natural fungicide — as a preventative measure on susceptible plants on a weekly basis.

To make a natural neem oil spray:

Combine 1 tablespoon cold-pressed neem oil with 1 teaspoon liquid soap in a jar. You can use dish soap or something like Dr. Bronner’s liquid castile soap. Add warm water to the jar and shake until thoroughly combined. Then shake a little more. (It needs to be really well combined.)

Pour mixture into a one-gallon sprayer and add water to the one-gallon mark. Thoroughly drench leaves and stems of garden plants.

Optional: I like to add a tablespoon of liquid kelp to the mixture while I’m at it, to add some nutrients to the mix.

Dealing with infestations

5. As soon as you see signs of powdery mildew, take action. Trim off all leaves with visible spots. Try to jostle the plant as little as possible to avoid spreading spores. Discard leaves in the trash.

close up of fungus on leaf

6. Spray infested plants with neem oil weekly. Watch to see if the powdery mildew appears on new plant growth.

7. Remove heavily infested plants. If the neem oil spray doesn’t hold the mildew at bay, plants will fail to thrive and eventually die. Leaving a sick plant in the garden allows the spores of the powdery mildew to spread and infect other plants. If you have severe damage, it’s a good idea to remove the entire plant.

8. Don’t compost plant material that is damaged; the powdery mildew spores can remain in the compost. When you spread the compost, you’ll spread those spores.

powdery mildew on squash plant

More things to try:

A study in Australia found that milk diluted at 10% strength would stop the growth of powdery mildew, when sprayed on the leaves. Whey, left over from cheese making was also effective. Kefir, yogurt, and other fermented milk products that are past their prime would work as well. A 10% solution is about 1-2/3 cups of milk per gallon of water. Plants should be sprayed every two weeks to deter powdery mildew.

Sources:

  • http://ipm.ucanr.edu/PMG/PESTNOTES/pn7406.html
  • https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5061770/

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Meet the Author

Kris Bordessa

Kris Bordessa founded Attainable Sustainable as a resource for revitalizing vintage skills. Her book, Attainable Sustainable: The Lost Art of Self-Reliant Living (National Geographic) offers a collection of projects and recipes to help readers who are working their way to a more fulfilling DIY lifestyle.

4 comments… add one
  • Cheri Jun 18, 2020, 6:12 am

    Thank you for this timely advice on Powdery Mildew. I noticed one of our squash plants has been affcted last week. I got some Neem oil and am going to mix it with the dish soap as you recommended. Gosh, I hope this works! We have a LOT of squash plants. Thanks Again!

    • Karen Jul 15, 2020, 4:36 am

      How much water do you add to the neem oil and dish soap?

  • Nan Bailey Jun 18, 2020, 12:56 pm

    Do you think sprinkling cinnamon powder on the affected leaves would help as well?

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