Why Is There White Powder on My Leaves? A Guide to Powdery Mildew

Quick Diagnostic Chart

Hello, plant friends! Anastasia here. If it looks like someone has dusted the leaves of your plant with a fine, white powder, you’re almost certainly looking at powdery mildew.

This is one of the most common and recognizable fungal diseases on houseplants. It starts as small, circular white spots and can quickly spread to coat an entire leaf. Don’t worry-it’s treatable if you act quickly.

A Common Fungal Disease

Powdery mildew is a parasitic fungus that lives on the surface of plant leaves. Unlike many other fungi that require water to be present on the leaf, powdery mildew can thrive in conditions of high humidity and stagnant air alone.

The white powder you see is a combination of the fungus’s thread-like structures (mycelium) and its spores. These spores are easily carried by air currents to other leaves and other plants, which is why it can spread so quickly. The fungus inserts tiny feeding tubes into the leaf’s cells, stealing nutrients and blocking sunlight, which slowly weakens the plant.

Powdery mildew is one of the most common fungal diseases, but it’s not the only one. You can learn to spot others in our main guide to Fungal & Bacterial Diseases.

The Main Cause: Poor Air Circulation & High Humidity

Powdery mildew spores are virtually everywhere. They only become a problem when they land in an environment that is perfect for their growth. The ideal conditions for powdery mildew are:

• Poor Airflow: This is the #1 factor. Stagnant air allows humidity to build up around the leaves, creating a perfect microclimate for the fungus to grow.
• High Humidity: While it doesn’t need wet leaves, the fungus loves humid air (typically above 70%).
• Low Light: Plants in dimmer spots are more susceptible as they are often weaker and have less energy to fight off infection.

The Fix: A 4-Step Treatment Plan You must treat the plant and fix the environment.

Step 1: Isolate the Plant The spores are airborne. Immediately move the infected plant far away from all your other houseplants to prevent it from spreading.

Step 2: Prune the Worst of It If any leaves are completely covered in mildew, it’s best to prune them off with clean scissors. Seal them in a plastic bag and dispose of them outside.

Step 3: Wipe the Leaves Using a damp paper towel, gently wipe the mildew off the remaining leaves. This physically removes a huge number of spores and makes your treatment spray more effective. Use a fresh piece of paper towel for each leaf to avoid spreading spores.

Step 4: Treat with a Fungicide After wiping, thoroughly spray the entire plant-tops and bottoms of all leaves and stems-with a fungicide. Repeat this treatment every 7-10 days for several weeks.

• Neem Oil: A great organic option. It acts as both a fungicide and an insecticide. Mix according to the product’s directions and spray thoroughly.
• Baking Soda Spray: A classic DIY remedy. Mix 1 tablespoon of baking soda and 1/2 teaspoon of mild liquid soap (like castile soap) into one gallon of water.
• Commercial Fungicide: For severe cases, a store-bought fungicide specifically labeled for powdery mildew will be very effective.

Best Practices for Healthy, Clean Leaves

• Improve Air Circulation: This is the most important preventative measure. Give your plants space-don’t crowd them. Use a small, oscillating fan for a few hours a day to keep air moving around your plants.
• Increase Light: Move susceptible plants to a spot where they receive brighter, indirect light. A healthier, more energetic plant is better able to resist disease.
• Avoid High Humidity Swings: Try to maintain a stable environment. Water in the morning so the soil surface can dry during the day.
• Inspect Plants Regularly: Catching the first few spots of powdery mildew is much easier to treat than a full-blown infection.

Which Plants are Most Susceptible?

Is powdery mildew the same as mealybugs?

Will powdery mildew kill my plant?

Can I just wipe the white powder off?