How to Get Rid of Powdery Mildew
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.
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.
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.
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.
© 2014 Caren White