How to Get Rid of Powdery Mildew in Your Garden

Updated on March 25, 2019
OldRoses profile image

Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.

A watermelon vine that is infected with powdery mildew
A watermelon vine that is infected with powdery mildew | Source

Powdery mildew is a scourge of gardens, both vegetable and ornamental. There are some simple steps you can take to prevent powdery mildew or get rid of it once it infects your plants.

What is Powdery Mildew?

Powdery mildew is caused by fungus that is present in the soil. Although it looks the same throughout your yard, powdery mildew is caused by many different types of fungus, each specific to a particular plant. Fortunately, different species of fungus cannot spread to different kinds of plants. For instance, the powdery mildew infecting your lilacs cannot infect your zucchini. They are caused by two different fungi.

Fungi grow best in humid weather and shady locations. It infects your plants but doesn't kill them. It is unattractive in flowers and shrubbery. It is especially a problem in the vegetable garden because once infected, the leaves no longer photosynthesize (make food for the plant) so any fruit that is produced will be malformed and less flavorful.

How to Prevent Powdery Mildew

The best prevention is to plant flower and vegetable varieties that are resistant to powdery mildew. Failing that, do not plant susceptible plants in the shade which encourages growth of the fungi. Shade encourages moisture which in turn encourages the growth of fungi. Sunlight tends to dry out moisture, rendering the environment less hospitable to fungi.

Plant in full sun and do not crowd your plants to encourage good air circulation. Air that is moving between plants carries the fungi away from the plants. When plants are crowded, the air does not move between the plants and the fungi is able to stay on the leaves and infect them.

Apply fertilizer or compost in steady quantities rather than in periodic large amounts because the fungi prefers the new fast growing shoots. Slow release fertilizer is best because it supplies the plants with small amounts of fertilizer throughout the growing season.

Avoid watering from overhead. This will cause soil to splash onto your plants possibly infecting them if fungi is present in the soil. Always water at the roots or use drip irrigation.

It is important that you thoroughly clean up your garden in the fall. Fungi will over-winter in any garden debris that is left on the ground, emerging in the spring to infect your plants again.

Sprays That Prevent Powdery Mildew

You can purchase sprays at your local nursery to prevent powdery mildew. They contain sulfur or potassium bicarbonate which will prevent fungi from growing on your plants.

You can make your own spray by mixing 1 teaspoon of baking soda and 1 quart of water. The baking soda raises the pH of the leaves so that the fungus can't grow.

Whether you purchase a spray or make your own, you will need to reapply after it rains.

How to Get Rid of Powdery Mildew

Once your plants become infected, it is difficult to get rid of the powdery mildew. Remove any infected plant material so that the infection doesn't spread to other plants. Either throw it out or compost it.

Fungicide sprays made up of horticultural oils or plant based oils such as jojoba or neem oils, copper or potassium bicarbonate can be purchased at your local nursery or you can make your own fungicide spray. Mix 1 tablespoon of baking soda in a gallon of water and add ½ teaspoon of liquid soap.

Surprisingly, studies have shown that milk is effective in slowing the spread of powdery mildew on plants that are already infected. Mix 1 part milk to 9 parts water and spray on plants showing signs of powdery mildew.

As with any spray, you will need to re-apply after any rain.

Powdery mildew is ugly but it won't kill your plants. Prevention is always best because once it infects your plants it is difficult to get rid of it as well as stop it from spreading to other plants.

Questions & Answers

© 2014 Caren White

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    • profile image

      Janet Tanner-Tremaine 

      2 weeks ago

      Hello Caren - This is more about brassica caterpillars (little green, major munching little beasts) and an organic homemade solution to get rid of the. I think that they are laid on the leaves of cauliflower etc by a white butterfly. It is too late for my crop this year and we have pulled out all the plants affected and will start again - maybe next year!

      I would be most grateful if you could recommend something not too complicated we could mix at home and spray the plants as they grow.

      Many thanks

      JanTT

    • OldRoses profile imageAUTHOR

      Caren White 

      4 years ago

      Your welcome Pawpaw! The older zinnia varieties are prone to powder mildew no matter how careful you are. One of the features on the newer hybrids is their resistance to powdery mildew. The same with lilacs. I treasured my old-fashioned lilac despite its annual attack of powdery mildew. The new ones are pretty and the leaves stay green rather than turning gray, but they just don't have the same sentimental value for me. Thank you for reading and commenting.

    • Pawpawwrites profile image

      Jim 

      4 years ago from Kansas

      I have a little on some of my Zinnias, which catch a little spray, at the edge of where our lawn sprinklers reach. Thanks for the excellent information.

    • OldRoses profile imageAUTHOR

      Caren White 

      5 years ago

      Flourish, so glad that you found it useful. Thanks for reading and pinning.

    • FlourishAnyway profile image

      FlourishAnyway 

      5 years ago from USA

      This is very useful. Voted up and pinning to my gardening and outdoors board.

    • OldRoses profile imageAUTHOR

      Caren White 

      5 years ago

      Peggy, I was surprised about the milk too! Thanks for reading and pinning.

    • Peggy W profile image

      Peggy Woods 

      5 years ago from Houston, Texas

      Thanks for this information about how to treat powdery mildew. That is interesting that milk works in treating it. Good old baking soda to the rescue mixed with water is certainly an easy approach. Living in humid Houston, it can sometimes be a challenge to combat powdery mildew especially since we have a sprinkler system that hits plants with water from above. Pinning to my gardening board.

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