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How to Treat and Get Rid of Powdery Mildew on Plants Naturally

A common garden blight, how to get rid of powdery mildew is a common question and challenge for gardeners. But before we get into how to treat powdery mildew naturally, it’s helpful to get to know this garden enemy and what we’re dealing with.

Yuk! What’s that white stuff on the leaves? If your plants have been attacked by powdery mildew, you know the frustration and challenge of this garden nemesis.

What is Powdery Mildew?

Powdery mildew is a fungus that can quickly weaken plants and compromise production. 

Powdery mildew afflicts plants in much the way yeast or candida overgrowth afflicts humans. Yeast is naturally everywhere in nature, on foods and in the body. It’s when the yeast gets out of balance that problems occur.

It’s the same with powdery mildew spores. They’re in the air floating around looking for a place to land and grow. When the conditions are right, they move in to stay, reproduce and spread.

The good news is that you can treat powdery mildew to keep your plants vibrant. We’ll get to remedies in a minute, but first some answers and images.

What Does Powdery Mildew on Plants Look Like?

Very aptly named, powdery mildew appears as unmistakable white splotches and blotches on the leaves of plants. It looks like someone came out with the talcum powder and randomly vigorously plastered the plants with it.

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Powdery mildew on plant leaves.

How to Get Rid of Powdery Mildew?

Unfortunately, you can’t get rid of powdery mildew completely. But you can keep it at bay.

Yes, You Can Treat Powdery Mildew Organically

While it’s a hassle, you can treat powdery mildew using natural remedies that will save your crops, IF, you get to it in time and are diligent in application.

White powdery mildew is a fairly common problem, so if you haven’t yet encountered it, that’s great, but file this away, just in case. You can have vibrant green leafed plants that seem to be thriving, but then this icky white blight looking stuff can still appear.

Can Powdery Mildew Spread to Other Plants?

Yes, unfortunately, powdery mildew can quickly spread to affect other plants, so you’ll want to treat afflicted plants right away and keep at it everyday.

We made a big mistake last year and didn’t check in soon enough on our goji berries at our cabin garden. (We don’t live on that property yet). Subsequently we lost last year’s crop of gojis, so we’ll definitely keep a closer eye on that from now on.

The Bad News:
Powdery mildew is very common, can spread and is virtually impossible to cure.

The Good News:
Powdery mildew is easy to treat and keep under control.

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How to Treat Powdery Mildew Naturally

We’ve been routinely spraying neem oil mixed with liquid BT and now that the powdery mildew has appeared, we’ve added another organic control spray (bacillus subtillus).  Interesting how a fungus-like bread mold can be converted to bacteria-fighting penicillin, and a bacteria can be developed to combat a fungus-like powdery mildew.

The product we’re using is made by “Serenade” and is OMRI-approved.* You can even spray and harvest the same day.  Be sure to store at room temp, cover both upper and lower leaf surfaces till run-off, and carefully follow the label instructions.

*What is OMRI? OMRI stands for Organic Materials Review Institute.[1]

There are other organic type fungal treatments that contain copper, sulfur, or potassium bicarbonate. In the past, we’ve tried home cures of milk, baking soda, and hydrogen peroxide with little effect. So this season, it’s just the neem oil, the BT, and now, the Serenade sprays.

The results? Manageable.

The bottom line with Powdery Mildew? You can’t get rid of powdery mildew completely, but you can slow it down to manageable.

The Best Time to Treat for Powdery Mildew is Before it Starts

It’s best to spray and protect plants before there is an issue. When it is humid, leaves are more prone to having mildew issues. Spray the leaves to coat on both sides once a week and after rain.

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Steps in Treating Powdery Mildew

  1. Prevention is best – spray plants with treatments to prevent powdery mildew from attacking your plants.
  2. Remove and burn affected parts. Wash hands and tools thoroughly as powdery mildew spreads easily.
  3. Spray both sides of leaves thoroughly, plus stems, out of direct sunlight.
  4. Re-apply spray weekly and after rain.

Natural Treatments for Powdery Mildew

You can buy ready made fungicides or you can make your own natural treatments at home.

  • Neem oil and water
  • Whole milk and water
  • Baking soda, water, soap and/or molasses
  • Hydrogen peroxide
  • Liquid BT (bacillus subtillus)
  • Serenade (OMRI approved)

With spray solutions, you need to spray the leaves and reapply after rain to treat powdery mildew.

Baking Soda Treatment for Powdery Mildew

This recipe works best as a preventive measure than a cure, though it will help lessen the impact of powdery mildew. This mixture is best used immediately rather than storing, so we’ve included a smaller recipe for if you have fewer plants to treat.

APPLICATION: Water plants a day or so prior to treatment. Do not apply in direct sunlight

Baking Soda Spray – Smaller Quantities – for fewer plants

  • 1 teaspoon baking soda
  • Couple drops of liquid dish soap
  • 1 quart water
  • 1 teaspoon molasses or horticulture oil (optional; but the oil helps smother the fungi)
  • Mix in spray bottle
  • Spray leaves liberally on both sides

Baking Soda Spray – Larger Quantities – for more affected plants

  • 1 Tablespoon baking soda
  • 1 teaspoon liquid dish soap
  • 1 gallon water
  • 1 Tablespoon molasses or horticulture oil (optional; helps smother the fungi)
  • Mix in spray bottle
  • Spray leaves liberally on both sides

Milk Spray

  • 1 Part milk  (approx. 3 oz)
  • 9 Parts water (approx 29 oz)
  • Mix in quart spray bottle
  • Spray leaves on both sides

Neem Oil

We like the natural quality of the neem oil, and that it’s the simplest to make and apply.

  • 2.5 Tablespoons Neem oil
  • 1 gallon of water
  • Apply weekly and after rain

How simple is that, right?!

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Powdery Mildew on Squash and Tomato Plants

Here’s Coleman talking about treating powdery mildew on squash and tomatoes in our lower garden.

Steps to Preventing Powdery Mildew – in Summary

What is powdery mildew?

Powdery mildew is fungal spores spread by wind and can overwinter on plants and in plant debris.

How does powdery mildew spread?

  • The wind carries fungal spores that take up residence on the leaves and stems of plants.
  • Powdery mildew can grow without direct contact with water.
  • Powdery mildew thrives in summer climates.
  • Spreads quickly from affected parts and plants, so quick action to treat it is imperative.

How to Get Rid of Powdery Mildew?

You can’t get rid of it, so prevention is best. If your plants get it, diligent powdery mildew treatment can keep it under control.

What Plants are Vulnerable to Powdery Mildew?

Powdery mildew affects ornamentals such as:

  • Beebalm (Monarda)
  • Lilacs (Syringa)
  • Zinnias
  • Roses
  • Garden phlox (P. paniculata)

Powdery mildew especially affects these vegetables:

  • Beans
  • Cucumbers
  • Grapes
  • Melons
  • Squash

What Does Powdery Mildew Do?

Besides being ugly, powdery mildew can negatively affect the flavor and yield of fruits and vegetables, and can even destroy entire plants, as has happened in our garden. Though plants do not usually die, their production is significantly hampered. If you want to keep your crop, treatment is imperative and urgent.

Powdery mildew coats the plant leaves, thereby significantly impairing the photosynthesis process. This interferes with the plant’s ability to convert sunlight and Co2 into oxygen and the nutrients it needs to thrive and produce.

When it comes to ornamentals, powdery mildew doesn’t usually kill them, so treatment is optional. However, no gardener likes to see powdery mildew on his or her prize roses!

How to Prevent Powdery Mildew Organically

Powdery mildew can’t be cured, so every effort at prevention is the best defense.

  • Plant mildew resistant or mildew tolerant varieties
  • Place plants for the best air circulation
  • No overcrowding of plants
  • The more direct sunlight, the better, to inhibit spore germination
  • Burn affected plants or bag and trash them

Powdery mildew prevention and treatment is possible; cure is not.

For more images and an update on our powdery mildew issues and treatments, you may enjoy this newsletter article.

SOURCE: Rol Staff, on[2]

Contributions from the Community

Rather than use vinegar in the mixture ( which is terrible for the soil ) to combat powdery mildew, use whole milk and water.

It’s best to spray and protect the leaves before there is an issue. Keep in mind when it is humid, leaves are more prone to having mildew issues. The whole idea is to coat the leaves on both sides. Spray once a week, unless it rains, in which case you just spray once again. 
~Susan Carpenter

I’ve used a mix of backing soda and water with a touch of soap or molasses for powdery mildew on crape myrtles. Works great!
~Elizabeth Russ 

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Wishing you great gardens and healthy harvests!


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