Happy August, everyone! We’re back with another Ask Anna your Gardening questions! This month, we are answering “My plants are covered in a white powdery coating on the leaves. What is it, and is there anything I can spray at home to stop it?”
That white, dusty coating is most likely powdery mildew, one of the most common fungal diseases in the garden. The good news is that it usually looks worse than it is. While it can weaken plants over time, catching it early often makes a big difference.
Powdery mildew thrives when days are warm, nights are cool, and air circulation is poor. You’ll often see it on zucchini, cucumbers, squash, bee balm, phlox, roses, and even lilacs. Unlike many fungal diseases, it doesn’t need soaking rain to spread.
The first step is to remove the worst affected leaves and throw them in the garbage—not the compost pile. This helps reduce the number of fungal spores that can spread to healthy growth.
There are a few home remedies that gardeners have had success with. One popular option is a baking soda spray. Mix 1 tablespoon of baking soda, 1 teaspoon of mild liquid dish soap, and 4 litres of water. Spray both the tops and undersides of the leaves every 7 to 10 days. Spraying in the morning so it has time to dry during the day. Another option is 1 part milk to 9 parts water. Sprayed once a week. Some studies suggest the natural proteins in milk can help slow the disease when used regularly.
Always test any homemade spray on a small section of the plant first, especially during hot weather, as leaves can sometimes be sensitive. Overly wet leaves can sometimes encourage other fungal diseases.
The best long-term defense is prevention. Space plants properly, water at the base instead of over the leaves, and avoid excessive nitrogen fertilizer, which encourages tender new growth that powdery mildew loves.
Remember, a little white powder doesn’t mean your garden is doomed. With quick action and good growing practices, most plants recover nicely and continue producing all season long.
If you have gardening questions or need advice, feel free to reach out! You can send your questions to me at [email protected] with the subject line “Ask Anna,” and I’ll happily feature your questions in next month’s NewsMagazine.
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