How to Prevent and Treat Powdery Mildew

Learn how to prevent and treat powdery mildew before it causes problems with the fruits and vegetables growing in your garden.

What is powdery mildew? Powdery mildew is a disease caused by several types of fungi. It first appears as a whitish-gray powdery coating on the surfaces of plants, eventually turning the leaves yellow or brown. Left untreated, powdery mildew quickly spreads by spores on wind or physical contact, and damages or destroys crops.

Disclaimer: this post contains affiliate links. See my disclosure policy for more information.

Learn what powdery mildew looks like so you can begin to combat it when it first appears.

Roses	New flower buds are covered in white powder.
Raspberries	Undersides and tips of leaves become deformed.
Cantaloupe	Leaves and stems turn brown; poor fruit production.
Peas	White spots on leaves and pods; stunts vines.
Zinnias	Mildew covers leaves, buds, and stems.
Squash	White spots on tops and undersides of leaves/vines. (Tip: Know what you are growing. Many varieties of squash have variegated leaves that may look like powdery mildew.)
Apples	White patches on the leaves, fruit, and stems.

7 Tips for How to Prevent and Treat Powdery Mildew

1. Plant powdery mildew-resistant varieties.

If powdery mildew has been an issue in the past, plant disease-resistant varieties of crops known to be susceptible to powdery mildew such as cantaloupe, zinnias, roses, squash, and peas.

2. Prune or stake plants to improve air circulation.

An abundance of foliage or vines left sprawling on the ground are inviting to pests and diseases. Proper air circulation helps prevent fungal diseases. Prune and trellis plants to allow as much air and sunlight as possible to reach the plants.

3. Water correctly.

Water in the morning. Evening watering creates a cool, damp climate that promotes powdery mildew and other fungal diseases.
Using drip irrigation (rather than overhead) puts the water on the soil (where it is needed) rather than on the leaves.
Do not over-water. Let top inch or two of soil dry out between waterings. Damp soil promotes fungal diseases.
For more information, read this article about correct watering.

4. Keep plant debris cleaned up to prevent powdery mildew.

Leaves and trimmings from plants can harbor fungal spores. Rake up and remove debris from around plants.

5. Use a baking soda solution, milk solution, or potassium bicarbonate solution to prevent and treat powdery mildew.

Choose one (or more) of the following methods. Continue treatment while warm, humid conditions remain to prevent further infections.

Treat with baking soda / castile soap solution to remaining leaves every 7 days. Use 1 teaspoon baking soda plus 1 teaspoon liquid castile soap per quart of water in a spray bottle. Apply as a preventative or to stop early outbreaks.
Treat powdery mildew with a milk solution every 7-10 days. The protein in milk may create an antiseptic effect when exposed to sunlight. Use a 40% milk to 60% water solution. Spray on leaves of affected and nearby plants, lightly coating all surfaces while the sun is shining for best effect.
Mix 1 tablespoon of potassium bicarbonate powder and 1 tablespoon of liquid castile soap in 1 gallon of water and spray all parts of the plant well. Spray plants every 7-14 days to treat an outbreak.

6. Remove affected leaves or plants, and destroy them.

An effective method for preventing further powdery mildew is to remove and destroy affected leaves as you see them. Sanitize hands, gloves, and tools that come in contact with the diseased leaves.