For daily wit & wisdom, get the Almanac newsletter.

How to Prevent and Control Powdery Mildew

powdery mildew plant disease on a yellow summer squash plant and leaves
Image Credit:
AJCespedes/Shutterstock
Written By: Catherine Boeckmann Executive Digital Editor and Master Gardener

Wondering about white spots and splotches on your plants? The fungal plant disease called powdery mildew is a common problem in gardens, infecting a wide variety of plants and reducing the quality and quantity of flowers and fruit. Learn how to identify, prevent, and treat powdery mildew.

What is Powdery Mildew?

Powdery mildew is a fungal disease that affects a wide variety of plants. There are many different species of powdery mildew, and each species attacks a range of different plants. In the garden, commonly affected plants include:

When the fungus begins to take over one of your plants, a layer of mildew made up of many spores forms across the top of the leaves. These spores are then carried to other plants by the wind. Powdery mildew can slow down the growth of your plant and, if the infection is severe enough, will reduce fruit yield and quality.  According to Gary W. Moorman, Ph.D., of Pennsylvania State University, “All the powdery mildew fungi are obligate parasites, requiring live tissue to grow and reproduce.”

How Does Powdery Mildew Spread?

Powdery mildew spores typically drift into your garden with the wind. Still, if you’ve had powdery mildew occur in the past, new outbreaks may also arise from dormant spores in old vegetative material or nearby weeds.

Unlike many other fungal diseases, powdery mildew thrives in warm (60°–80°F / 15°–27°C) and dry climates, though it requires fairly high relative humidity (i.e., humidity around the plant) to spread. In cooler, rainy areas, it does not spread as well, and its growth is also slowed by temperatures higher than 90°F (32°C). It tends to affect plants in shady areas more than those in direct sun.

Identification

How to Identify Powdery Mildew

  • Plants infected with powdery mildew look as if they have been dusted with flour.
  • Powdery mildew usually starts as circular, powdery white spots, which can appear on leaves, stems, and sometimes fruit.
  • Powdery mildew usually covers the upper part of the leaves but may grow on the undersides as well.
  • Young foliage is most susceptible to damage. Leaves turn yellow and dry out.
  • The fungus might cause some leaves to twist, break, or become disfigured.
  • The white spots of powdery mildew will spread to cover most of the leaves or affected areas.
  • The leaves, buds, and growing tips will also become disfigured. These symptoms usually appear late in the growing season. 

Not certain yet? Use the Almanac’s Plant Problem ID tool to understand out what’s wrong with your plant.

Control and Prevention

How to Prevent Powdery Mildew

As with all pests and diseases, the best means of controlling powdery mildew is proactive prevention. 

  • Choose plants for your garden that are resistant to powdery mildew. Many mildew-resistant varieties of cucurbits (melons, cucumbers, squash, etc.) have been developed and are available from major seed suppliers.
  • Plant in sunnier spots, as powdery mildew tends to develop more often in shady areas.
  • Selectively prune overcrowded areas to increase air circulation around your plants; this helps to reduce relative humidity.
  • Watering from overhead can help to wash spores off leaves. However, wet foliage can often contribute to developing other common diseases, so it’s best not to rely on this as a prevention tactic.

Homemade Powdery Mildew Prevention

Effective organic fungicides for treating powdery mildew include sulfur, lime-sulfur, neem oil, and potassium bicarbonate. These are most effective when used before infection or when you first see signs of the disease.

  • Baking soda has been proven by many gardeners to be effective in treating powdery mildew. Mix 1 teaspoon of baking soda in 1 quart of water. Spray plants thoroughly, as the solution will only kill the fungus that it comes into contact with.
  • Milk spray is another effective home remedy. Dilute the milk with water (typically 1:10) and spray on roses at the first sign of infection or as a preventative measure.

Fungicides

There are many fungicides, especially for rose bushes, that are highly effective with low toxicity, no residue, and long duration. One example is Triadimefon. It can be sprayed with 1000–1200 WP of 15% wettable powder, 1 time intervals of 10 days, and 2–3 times. But check with your local nursery for fungicides approved in your area.

How to Control Powdery Mildew 

Once plants are heavily infected, it’s very difficult to get rid of the disease, so focus on preventing it from spreading to other plants. Remove all infected foliage, stems, and fruit and destroy them, either by throwing them in the trash or by burning them. Do not compost any infected plant, as the wind can still spread the disease and persist in the composted materials.

After pruning off infected parts, do not allow pruning shears to touch healthy leaves. First, sterilize your pruners with rubbing alcohol.

Plant Disease

About The Author

Catherine Boeckmann

Catherine Boeckmann

Executive Digital Editor and Master Gardener

Catherine Boeckmann is the Executive Digital Editor of Almanac.com and a Purdue University Extension Master Gardener. She loves helping readers find practical, trustworthy answers—whether they’re figu...

Read more from Catherine Boeckmann

More Like This

Comments

<span>Kittygirl44</span> Wed, 11/19/2014 - 23:23
I bought a lilac bush (a young plant) a few months ago and a few days later I noticed it had powdery patches on it. I suspect it is powdery mildew. I planted it in my backyard a month ago. I didn't know what to do about the powdery patches so I haven't done anything about it yet. My lilac bush hasn't grown at all since I bought it and this concerns me. It is in partial sun--it gets the sun from the morning, and is shaded by trees in the afternoon. Any suggestions? Does it just take forever to grow? Will the powdery mildew kill it if I don't do anything? Please reply with suggestions. Thanks.
<span>Jeremey Jones</span> Mon, 03/23/2015 - 09:17
hey i had powdery mildew bad last year and my buddy had the same issue so we figured a little cure searching was in order so after losing all of my tomatoes and most of my peas i found this stuff called cuh2o and i guess all this is, is copper and water when i called the number the people told me it was used for years and so i asked whats so special they literaly just told me its the copper suspended in watter and its pattend or whatever yadda yadda epa yada all that jazz and so i says send me a bottle and man with in the week i called em back and gave them my blessing cuz it kicked butt i mean i now have no sings of powder and it dont leave the nasty residue but any who ill share the number with you so u can combat and rid your plants of mildew your not alone with the problem and it dose suck the life out of em but ya heres the number 616-226-6539
<a title="View user profile." href="/author/editors">The Editors</a> Thu, 11/20/2014 - 10:01

Your lilac tree is still young and you just planted it. It will grow more in the spring and next summer. Powdery mildew is common on lilacs after a hot humid summer. It's not going to hurt your bush. Lilacs need about 6 hours of full sun a day to bloom well. Go to our lilac page to find more tips about growing lilacs.

http://www.almanac.com/plant/lilacs

 <span>Melissia L</span> Fri, 09/12/2014 - 19:39
how do I keep Beatles off rose bushes
<a title="View user profile." href="/author/editors">The Editors</a> Mon, 09/15/2014 - 10:25

This is our powdery mildew page.  You can find more information on our Roses page as well as our Japanese Beetles page here:

http://www.almanac.com/plant/roses

http://www.almanac.com/content/japanese-beetles

You need to handpick these beetles and drop into pails of soapy water. You could also place fine netting over the rose bush.  Another idea is to get ride of the grubs in the lawn with Milky Spore. Finally, you could use an insecticide; speak to your local garden center about what's approved in your area.

 <span>Dave Wright</span> Thu, 07/03/2014 - 11:30
The top of our raspberry plants are dieing. what causes this?
<span>Jessika840</span> Fri, 04/11/2014 - 14:56
Last year was my first year growing a garden by myself. All the vine type plants (pumpkins, squash, melons, etc.) were killed by powdery mildew. They were doing great at first, by the end of summer the powdery mildew spread and rotted all the fruit and veggies. It was suggested to me that I burn the garden last fall, but I didn't get a chance to do it. In a month it will be time to plant the garden again. Will the mildew come back because I didn't burn the garden? Is there anything I can do now before I plant to prevent the powdery mildew from returning?
<span>Laura Shaffer</span> Sun, 05/04/2014 - 11:25
Pumpkins are heavy feeders and I would plant them in a different area this year. Be shure to feed your last year's garden with a good compost or other natural amendments. I always rotate heavy feeders every year and plant a cover crop to till in for the following year. Burning diseased plants or putting them in the trash is a good idea. I wouldn't plant a heavy feeder in the same spot for two or three years. If you don't have the room to rotate then feed the soil heavily. I like a mulch of at least 6 to 8 inches but pull it aside to get your plants into the soil. Happy gardening!
<a title="View user profile." href="/author/editors">The Editors</a> Mon, 04/21/2014 - 17:41

Some sources advise burning the infected plant materials that were affected with powdery mildew in the same season. Hopefully, you at least cleaned the garden of any infected plants. If you have not yet, do that as soon as you can and avoid shaking any residue that might be infected into this year's garden bed. The spores can overwinter on affected plants and it can fall off as you move plant residue.

As for this season, plant resistant varieties for better results. Plant in full sun. Avoid excess fertilizer (hard to know how much for you would be "excess"; follow fertilier guidelines). Provide youor plants with good air circulation; give the adequate (or slightly more) space between each.

If you do see signs of powdery mildew returning, prune to remove the infected branches or shoots as soon as you can. 

We hope you have a happy harvest this year.

 <span>Dawn Burgess</span> Fri, 09/06/2013 - 17:00
My Rose bush has Black Spot. Is there a home remedy to remove the Black Spot? Thank You