蜜桃恋人

How to Prevent and Control Powdery Mildew

powdery mildew plant disease on a yellow summer squash plant and leaves
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Identify the Powdery Mildew Plant Disease

Catherine Boeckmann
Pest Type
Plant Diseases

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 , of Pennsylvania State University, 鈥淎ll the powdery mildew fungi are obligate parasites, requiring live tissue to grow and reproduce.鈥

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 come from dormant spores in old vegetative material or weeds nearby.

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

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Identification

How to Identify Powdery Mildew

  • Plants infected with powdery mildew look like 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. 
Gardening Products
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 can be bought 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鈥1200 WP of 15% wettable powder, 1 time intervals of 10 days, and 2鈥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 loves nature, stargazing, and gardening so it鈥檚 not surprising that she and The Old Farmer鈥檚 蜜桃恋人 found each other. She leads digital content for the 蜜桃恋人 website, and is also a certified master gardener in the state of Indiana. Read More from Catherine Boeckmann
 

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Comments

Janice (not verified)

4 years 4 months ago

What can u do to stop moody garlic and is it safe to eat? What about planting next year?

DON W (not verified)

4 years 12 months ago

I have found that a mixture of 3% hydrogen peroxide with insecticidal soap works very well at controlling both powdery mildew and insect pests. I buy 27% h2o2 at the local farm supply and dilute it 1 quart to 9 quarts water, and add the insecticidal soap in my backpack sprayer. I spray all my fruit trees at the first hint of the fungus, and this keeps the trees happy for several weeks. I too am in the PNW.

Brian (not verified)

5 years 3 months ago

My Japanese Maple looks like it has this powdery mildew. I sprayed a few leaves with some 鈥渟even鈥, hope I didn鈥檛 kill it more. A week or so back I noticed something odd, went on vacation and now it has spread quite a lot. I read here that all infected leaves should be removed and destroyed...yikes. Will the other options (Milk & water or baking soda) work without removing the infected parts?

sonya Norton (not verified)

5 years 4 months ago

Bicarb works, but I'm never sure if i overdid it. I'm a firm believer in milk and water as a spray. It doesn't seem to matter of it's skimmed milk or whole milk. 50/50 with water, weekly or after rain. Has even beaten the mildew on lupins, my worst sufferer here in the PNW.

The stink bugs have destroyed majority of my blackberry bushes/plants. Help how do I prevent this for next years crop.

richard h hoyt (not verified)

5 years 4 months ago

Implement Lactobacillus Serum as a preventive and you won't get PM. Google search on how to make. Really simple.

Payton Jett (not verified)

5 years 3 months ago

Once I make this, how do I implement?

Annie Herbert (not verified)

5 years 1 month ago

Will I have to dig up new plants .honey suckle .

Sian (not verified)

5 years 5 months ago

Hey, there! I just noticed a peculiar thing I've never seen before; three leaves of my rose-scented geranium have what appears to be salt in their gullies. I thought at first I was looking at powdery mildew (a familiar foe), until I noticed the loose, sparkling quality of the substance. Are the leaves leaching salt? I do not fertilize, never need to, and the effected leaves still look as healthy as ever (I have still removed them in case the substance is otherwise nefarious). What could this be? For information's sake, this geranium is planted in a half-gallon SmartPot.

Ron Lane (not verified)

5 years 5 months ago

This is one of the better PM articles I have seen on the net. One correction is that baking soda does not stop powdery mildew, it only helps to prevent it. You may spray it on and think your PM is gone, but if you come back in a couple of hours your PM has returned.
Pristine is a BASF product that actually eliminates PM. Some form of it might be available to homeowners. Of the softer chemistries, Circadian Sunrise is the only one I've seen that consistently stops PM cold. The problem with that product is that the smallest unit presently sold is a 2.5 lb concentrate, which is far more product than most homeowner will use in their gardens over the course of a year or more.