Preventing Powdery Mildew

To prevent powdery mildew, full sunlight is preferred and overcrowding of plants should be avoided.

Related To:

Powdery Mildew

Powdery Mildew

Powdery mildew is a broad term for a variety of fungi affecting a wide range of plants. Its unsightly powder on the surface of leaves, flower petals and stems is rarely fatal to plants.

Photo by: Image courtesy of University of Georgia Plant Pathology Archive, University of Georgia, Bugwood.org

Image courtesy of University of Georgia Plant Pathology Archive, University of Georgia, Bugwood.org

Powdery mildew is a broad term for a variety of fungi affecting a wide range of plants. Its unsightly powder on the surface of leaves, flower petals and stems is rarely fatal to plants.

Powdery mildew is a catch-all name given to a variety of fungi affecting a wide range of plants including flowers, vegetable plants and ornamental trees. Most often manifesting as a grey to white blanket of unsightly powder on the surface of leaves, flower petals and stems, powdery mildew is rarely fatal, but may impact photosynthesis causing leaf loss or discoloration and create plant stress leading to secondary problems. Affected buds may fail to flower and fruit-bearing plants can experience decreased production or diminished flavor of the fruit itself.

Overwintering in plant debris, powdery mildew will surface in the spring, spread by wind, insects or water splashed between plants. Most common in warm, high-humidity conditions, once the spores have found a suitable host, it does not invade the tissue, but coats outside surfaces. It feeds by anchoring root-like appendages called haustoria into epidermal cells.

Each type of fungi in the family of diseases called powdery mildew requires specific hosts to thrive. Mildew found on one plant may have no impact on neighboring plants of different varieties. Mildew found on squash, for example, may not impact nearby roses.

Cultural control is the first line of defense against powdery mildew. In regions where mildew is common, many plants like roses and vegetable plants have been developed to be resistant to powdery mildew. All plants should be kept healthy and planted in conditions for optimal health and growth. Full sunlight is preferred and overcrowding of plants should be avoided. Plants spaced too close together promote air stagnation and raise humidity beneath leaves, conditions in which powdery mildew thrives.

Use soaker hoses to water plants. Overhead watering is not generally advised, but can potentially reduce short-term problems with powdery mildew by washing spores from leaves. It does, however, also adversely increase relative humidity, which encourages spore development. Overhead watering should be done in the morning to give plant surfaces adequate time to dry in the sunlight.

When powdery mildew is detected on plants, immediately remove and destroy affected plant parts, including leaves, stems and flowers. Prune plants to improve air circulation and, if necessary, cull overcrowded plants. Because powdery mildew prefers young, succulent growth, during this time, fertilization should be suspended until plants are free of mildew. Any overhead watering should be discontinued, using soaker hoses or hand watering at the roots.

If cultural controls are ineffective or the stress impact is too great, chemical intervention may be necessary. Common treatments include, but are not limited to, sulphur, neem oil or horticultural oils.  Before applying fungicides, confirm the affected plants and select fungicides appropriate to the variety of powdery mildew present. As with all chemical treatments, follow instructions carefully regarding volume, duration and frequency.

When powdery mildew has been a problem in a vegetable garden, clear and destroy all plant debris from the plot once the growing season has ended. Do not compost these materials. Debris from all affected and neighboring plants should be burned or removed from the site to prevent overwintering of fungi.

Next Up

7 Ways to Prevent Tomato and Potato Blight

Early and late blight can affect both tomato and potato plants. Learn how to protect your garden and keep these diseases at bay by following these prevention tips.

What Do the Numbers on a Fertilizer Bag Mean?

What are N-P-K and the three numbers on a fertilizer label? They indicate the amount of nitrogen, phosphorus and potassium in the fertilizer. Read on to find out why those nutrients and their numbers are important for growing a lush lawn or healthy garden.

How Often Do You Water New Sod?

Thorough watering is crucial to your new lawn’s ability to develop strong roots. We’ll help you develop a system to stay on top of the most important part of lawn care.

How to Water Your Lawn the Right Way

Learn the ins and outs of lawn irrigation, including expert tips on how long to run the sprinkler.

The Latest USDA Plant Hardiness Zone Map and How It Works

The USDA just unveiled a new Plant Hardiness Zone Map and about half of the US has seen their growing zone shift upward. Find out if your zone changed and how to use that information to grow your best garden.

How to Design a Great Yard With Landscape Plants

Take the guesswork out of choosing landscaping plants by following "right plant, right place" garden design.

4 Ways to Convert Lawn to a Flower Bed

There are multiple methods for removing grass to create garden beds. Some are labor intensive while others just take time and patience. Here are four chemical-free ways to turn your lawn into your garden.

Lawn Seeding: How to Plant Grass Seed

To reinvigorate your existing lawn or plant a new one, follow these steps on how to grow grass in the spring and fall.

10 Best Garden Starter Kits on Amazon

Get your grow on with these easy-to-follow gardening kits for beginners.

Humane Ways to Get Rid of Groundhogs and Keep Them Away

Got groundhogs? Discover effective, all-natural ways to keep these critters out of your yard and garden.

Go Shopping

Get product recommendations from HGTV editors, plus can’t-miss sales and deals.

On TV

Follow Us Everywhere

Join the party! Don't miss HGTV in your favorite social media feeds.