How to Get Rid of Powdery Mildew

Updated on December 12, 2017
OldRoses profile image

Caren White is a Master Gardener and instructor at Home Gardeners School. She has been a volunteer at 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.

Know your enemy

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, it 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. Powdery mildew is especially a problem in the vegetable garden because once infected, leaves no longer photosynthesize (make food for the plant) so any fruit will be malformed and less flavorful.

Prevention

The best prevention is to plant varieties that are resistant to powdery mildew. Failing that, do not plant susceptible plants in the shade which encourages growth of the fungi. Plant in full sun and do not crowd your plants to encourage good air circulation. Apply fertilizer or compost in steady quantities rather than in periodic large amounts because the fungi prefers the new fast growing shoots.

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 our 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.

Preventative sprays

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.

Eradicating an active infection

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

Anti-Fungal Sprays

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 won't kill your plants. Prevention is always the best because once it infects your plants it is difficult to get rid of it and stop it from spreading to other plants.

Questions & Answers

    © 2014 Caren White

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      • OldRoses profile imageAUTHOR

        Caren White 

        3 years ago from Franklin Park, NJ

        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 

        3 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 

        4 years ago from Franklin Park, NJ

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

      • FlourishAnyway profile image

        FlourishAnyway 

        4 years ago from USA

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

      • OldRoses profile imageAUTHOR

        Caren White 

        4 years ago from Franklin Park, NJ

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

      • Peggy W profile image

        Peggy Woods 

        4 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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