Powdery Mildew

This year there seems to be an epidemic of powdery mildew at garden sites across the city.  It would be too easy to blame the source of the plants that have been affected, in this case our prime seed/plant benefactor “Keep Growing Detroit”, but since they only give away seeds of the affected plants, there has to be a larger force responsible for such a mass infection.  Personally, I have had this problem for over 5 years.  Some years were worse than others.  Not knowing what to do has been very problematic, especially since I have stopped planting some plants as a result.

The article below was found in my e-newsletter from Rodale Press and it clearly states what it is, the source, conditions and directions for dealing with this bothersome plant ailment.

Powdery Mildew



Here are steps you can take to prevent powdery mildew from blemishing your garden.


A gray, talcum powder-like coating that covers the leaves, flowers, and even fruit of some of your vegetables, perennials, and shrubs.

Where it’s a problem
Powedery mildew is found throughout North America

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.

Homemade Sprays
Research studies in 1999 and 2003 on infected zucchini and winter wheat (respectively) indicated that spraying cow’s milk slowed the spread of the disease.
To try this at home, mix 1 part milk with 9 parts water and spray the stems and tops of leaves with the solution. Reapply after rain.
Spraying leaves with baking soda (1 teaspoon in 1 quart water) raises the pH, creating an inhospitable environment for powdery mildew.

Now I have to admit that I was told about the milk spray technique this summer and I kind of pooh-poohed it.  I will have to correct myself to my associates and acknowledge that when it comes to gardening, I don’t know it all.  I’m alright with that because who does?  This shows that I need to do a better job of communicating and sharing with my fellow gardeners and listening to what they have to say, for they just might know what ails my plants and have a cure as easy  as a bottle of milk (diluted of course).


2 Responses so far »

  1. 1

    Nancy Bowman said,

    I have it on my lilac bush and it’s been bothersome because it looks as if it’s killing my beautiful bush…..gonna try it!
    Thank you!

  2. 2

    Yes try it and let me know how it worked.

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