Powdery Mildew: What is it & how to treat it

White powdery mildew on cucumber vine

If you garden in a humid climate, chances are you've encountered powdery mildew. This common fungal disease makes it look like someone dusted your plant leaves with baby powder. I recently battled it on my pink coneflowers this spring, and with a little TLC, my coneflowers are now thriving and stealing the show in my front yard!

What Is Powdery Mildew?

Powdery mildew is a fungal disease that can impact a wide variety of plants and vegetables. It flourishes in humid conditions and where there's poor air circulation. You'll recognize it by the distinctive white, powdery coating on your plant leaves. In the kitchen garden, some of the most susceptible plants include cucumbers, squash, zinnias, sage, bee balm, and echinacea.

How to Treat Powdery Mildew

Your eyes are your best defense against pests and disease, including powdery mildew. Regularly inspect your plant leaves, both on top and underneath.

Pruning and Airflow

At the first sign of powdery mildew, prune away any affected leaves and stems. You can also give the plant a "chop" to improve air circulation. When my coneflowers had powdery mildew this spring, I actually cut them almost to the base! While typically you shouldn't remove more than a third of a plant, I knew my coneflowers were well-established and would likely bounce back. Thankfully, all the new growth has been completely free of powdery mildew, and they're producing beautiful pink blooms where the butterflies land. And, remember to always sanitize your clippers after trimming diseased plants to prevent spreading the issue.

DIY and Commercial Solutions

If pruning doesn't fully resolve the powdery mildew, you can try a homemade solution:

Baking Soda Spray: Dissolve one tablespoon of baking soda in a gallon of water, add a few drops of liquid soap (like Dawn), and pour it into a spray bottle. Spray both the top and undersides of the leaves in the evening or on a non-sunny day to avoid scorching the foliage.

For an even simpler approach, consider a fungicide containing copper or try neem oil. Apply these solutions every seven days until the problem is under control.

The good news is that powdery mildew usually isn't fatal to your plants. However, it can weaken them because the diseased leaves aren’t getting as much sun as healthy ones, so early detection and treatment are key to keeping your garden healthy and vibrant.