Plant care guide
African Violet Powdery Mildew: Spot It and Stop It
Updated
Why does my African violet have powdery mildew?
Small circles of white or grey powder on the tops of African violet leaves, flowers or buds are usually powdery mildew. It spreads on crowded plants with poor air circulation, often in winter and early spring.
What to do first
Isolate the plant, pick off and discard the infected leaves and flowers, then space your violets apart and keep air moving with a small fan. Use a product only if it is labeled for indoor plants.
White dusty patches on a favourite African violet are alarming, but powdery mildew is one of the more manageable violet problems. Iowa State Extension’s answer on white blotches on African violet leaves calls it common on indoor plants. It says outbreaks typically occur in winter or early spring.
First make sure it is mildew, then change the conditions around the plant.
Is it powdery mildew?
Iowa State’s All About African Violets describes small circles of grey or whitish powder on the tops of the leaves. Missouri Botanical Garden’s page on powdery mildew indoors adds that it can cover buds and flowers too. Rubbing removes some of the growth, but not the fungus.
Rule out the common look-alikes on violets:
| What you see | More likely | Source |
|---|---|---|
| Pale rings, lines or blotches that do not rub off | Cold water on the leaves | Clemson, Iowa State |
| White cottony masses, often sticky, on leaves | Mealybugs | Iowa State |
| Fuzzy grey growth on soft, rotting tissue | Botrytis blight | NC State |
| Tight, crinkled centre leaves | Cyclamen mites | Clemson |
Clemson’s African violet factsheet says cold water causes white blotches and ring patterns on the leaves. Those are marks in the leaf, not powder on it. For a stunted, crinkled crown, see our cyclamen mite guide.
Why it shows up on violets
Iowa State says powdery mildew is more of a problem on overcrowded plants. Its FAQ names high relative humidity and poor air circulation as the conditions that favour it. Missouri Botanical Garden adds cool, damp conditions.
Shelves and light stands packed with violets fit that description. UC IPM’s powdery mildew Pest Note also lists shade and moderate temperatures of 16–27 °C (60–80 °F). That overlaps the 18–27 °C (65–80 °F) Iowa State gives for growing violets, so the room alone will not stop it.
Missouri Botanical Garden notes that each mildew fungus attacks a limited range of plants. Mildew on your violet may not be the same one on a nearby rosemary. Other African violets on the same shelf are still at risk.
What to do
- Isolate the plant. Missouri Botanical Garden advises this at the first sign of infection.
- Pick off infected leaves and flowers. Iowa State and University of Maryland Extension’s indoor powdery mildew page say a few infected leaves can be removed and discarded. Bag them rather than leaving them on the shelf.
- Space plants out. Iowa State recommends more spacing between plants and a small fan in the room.
- Keep leaves dry. Missouri Botanical Garden advises against wetting leaves. Iowa State notes that water left on violet leaves also causes spots. Water from below and empty the tray once the root ball is wet.
- Ease off fertilizer. Missouri Botanical Garden warns against high-nitrogen feeds, since mildew attacks new soft growth. Iowa State recommends a complete fertilizer at a low rate for violets anyway.
- Check the light. UC IPM notes that shade favours mildew. Violets need bright light without direct sun. Iowa State suggests north or east windows, or lights 10–20 cm (4–8 in) above the plants for 12–16 hours a day.
Products, if needed
Maryland says registered fungicides can be used, but removal and better airflow should help in most homes. Missouri Botanical Garden says to use a fungicide labeled for indoor use and follow the label.
UC IPM lists horticultural and neem oils for mild to moderate infections. Never apply oils above 32 °C (90 °F) or to drought-stressed plants. Test any product on a few leaves first, as Missouri Botanical Garden advises for baking soda sprays.
When to discard
Missouri Botanical Garden says to discard severely infected plants. If a favourite variety is badly affected, Purdue Extension describes rooting a single healthy leaf, so you can restart it from clean tissue. Check that leaf closely for powder first.
Our powdery mildew on houseplants article covers the disease across species and compares products in more depth. The African violet care guide, grow light comparison and African violet hub cover everyday care.
Related guides
Other african violet problems we cover: leggy growth, propagation, not blooming.
References
- Iowa State University Extension and Outreach: All About African Violets
- Iowa State University Extension and Outreach: What are the white blotches on my African violet leaves?
- Missouri Botanical Garden: Powdery mildew – Indoors
- University of Maryland Extension: Powdery Mildew on Indoor Plants
- UC IPM: Powdery Mildew on Ornamentals, Pest Notes
- Clemson Cooperative Extension, HGIC 1550: African Violet
- Purdue Extension HO-10-W: African Violets
- NC State Extension Gardener Plant Toolbox: Streptocarpus ionanthus
How this guide was put together: Iowa State University Extension, Missouri Botanical Garden, University of Maryland Extension, UC IPM and Clemson Cooperative Extension, Purdue and NC State Extension guidance.