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Treat Powdery Mildew on Plants

Yuk! What’s that white stuff on the leaves?

If your plants have been attacked by powdery mildew, you know the frustration!  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, and yes it can spread to affect other plants.

Powdery mildew can quickly weaken plants and compromise production.

The good news is that you can treat powdery mildew to keep your plants vibrant.

Powdery mildew on plant leaves.

We made a big mistake last year and didn’t check in soon enough on our goji berries at our upper 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 this season!

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

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

Homemade Powdery Mildew Sprays

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

Baking Soda Spray

  • 1 teaspoon baking soda
  • Couple drops of liquid dish soap
  • 1 quart water
  • Mix in spray bottle
  • Spray leaves liberally

Milk Spray

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

How simple is that, right?!

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

Steps to Preventing Powdery Mildew

Excerpted from an article by Rol Staff, on

Fungal spores are spread by wind and overwinter on plants and in plant debris. Unlike mildews that appear in bathrooms or basements, powdery mildew does not need direct contact with water in order to grow. The warm days and cool nights of late summer create an ideal climate for spore growth and dispersal.

Plants it attacks

Powdery mildew is the blanket name for a few different species of fungi that infect many ornamentals, such as beebalm (Monarda), lilacs (Syringa), zinnias, roses, and garden phlox (P. paniculata). It also affects vegetables, including beans, cucumbers, grapes, melons, and squash.

Why it’s a Problem

Powdery mildew is unattractive and it can affect the flavor and reduce yields of some fruits and vegetables. Although plants are unsightly and can be weakened by an infection, they do not usually die. Powdery mildew on ornamentals is an aesthetic issue, and not usually worth treating. Prevention and control is more important for vegetables.

Organic damage control

Powdery mildew can be prevented, and it can be controlled once it appears, but it can’t be cured. The key to preventing it is planting mildew-resistant or mildew- tolerant varieties. Resistant varieties get less mildew than susceptible varieties; tolerant varieties may get some mildew, but it shouldn’t affect the performance of the plant. Prevention also includes siting plants where they will have good air circulation, and exposing as much leaf surface as possible to direct sunlight, which inhibits spore germination.

To control minor infestations, pick off affected plant parts and either compost them in a hot compost pile or bag them tightly and put them in the trash.1)

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