Powdery Mildew: The White Dust on Leaves and How to Remove It

Do your leaves look dusted with flour? That's powdery mildew, one of the most common plant fungi. Though it looks alarming, it's one of the easiest to treat if you act early. It affects houseplants and the garden alike (zucchini, cucumbers and herbs are classics).

How to identify it

• A whitish-gray powder, like flour or talc, mostly on the tops of leaves.
• It starts in round patches and spreads.
• Over time, affected leaves yellow, deform and drop.

Unlike other fungi, powdery mildew doesn't need the leaf to be wet: it thrives in high ambient humidity with poor airflow.

Why it appears

• Stagnant air and crowded plants.
• High ambient humidity with little air circulation.
• Sudden temperature swings (typical in spring and fall).

Step-by-step treatment

1. Remove the worst leaves and bin them (not the compost).
2. Improve airflow and space the plants out.
3. Spray with one of these, covering tops and undersides:
   • Baking soda: 1 teaspoon per quart of water + a few drops of soap.
   • Diluted milk (1 part milk to 2-3 parts water), a surprisingly effective home remedy in the sun.
   • Sulfur or a specific fungicide for stubborn cases.
4. Repeat every 5-7 days until it's gone.

How to prevent it

• Airflow: don't crowd plants; let air circulate.
• Don't wet the leaves when watering; water the base.
• In the garden, choose resistant varieties and avoid excess nitrogen (soft new growth = more vulnerable).

Powdery mildew rarely kills a healthy plant, but it weakens and disfigures it. Treat it early and improve airflow. Not sure it's mildew? Upload a photo to the AI diagnosis.