Is it really powdery mildew?
Powdery mildew looks like someone dusted your plant with flour or talcum powder — white to grey patches that start on the upper surface of leaves and wipe off (temporarily) with a finger. Left alone, patches merge, leaves yellow and distort, and the fungus spreads to buds and stems. Don’t confuse it with these lookalikes:
| What you see | What it is |
|---|---|
| Dry white powder on top of leaves, wipes off | Powdery mildew |
| Fuzzy grey mould on dying tissue, damp feel | Botrytis (grey mould) |
| Cottony white clumps at leaf joints and stems | Mealybugs — a pest, not a fungus |
| White crust on the soil surface only | Mineral/salt deposits — harmless, flush the soil |
| Fine webbing and yellow speckles | Spider mites |
Unlike most fungal diseases, powdery mildew doesn’t need wet leaves to spread — it thrives in humid air combined with poor circulation, which is exactly what many homes provide. Begonias, African violets, kalanchoe, ivy and rosemary are frequent indoor victims.
Step 1: contain it
Move the infected plant away from its neighbours — spores travel on air currents. Snip off heavily coated leaves and bin them (don’t compost). Removing a few of the worst leaves cuts the spore load dramatically, but don’t strip more than about a third of the plant.
Step 2: spray
Three treatments have good evidence behind them. Whichever you use, coat both sides of every leaf and repeat every 7 days until you’ve seen no new powder for two weeks.
- Potassium bicarbonate — the top pick, because it kills existing mildew on contact rather than only preventing it. Mix 1 tablespoon per 4 litres of water with a few drops of liquid soap as a spreader. (Baking soda — sodium bicarbonate — works too but is a bit weaker and can leave sodium in the soil.)
- Neem oil — a preventive and mild curative. Follow the label dilution, spray in the evening, and keep the plant out of direct sun until dry to avoid leaf burn.
- Sulfur — an old, reliable fungicide for stubborn cases. Don’t use it within two weeks of an oil spray, above ~27 °C, or on sulfur-sensitive plants.
Step 3: fix the conditions
Sprays knock mildew back; conditions decide whether it returns. Powdery mildew loves stagnant, humid air, crowded foliage and big day–night humidity swings.
- Space plants so air moves between them; a small fan on low nearby works wonders.
- Keep relative humidity in the 40–60% band — see best humidity for houseplants.
- Water the soil, not the foliage, and water in the morning.
- Give plants enough light — weak, shaded growth is more susceptible.
Get warned before the white powder shows up
FloraCure watches your local weather and sends a powdery mildew risk alert when conditions in your area favour an outbreak — along with botrytis, downy mildew, leaf spot and root rot risk. And if you already see powder, scan the leaf: the AI confirms the diagnosis with a confidence score and gives you a treatment plan with specific products and active ingredients.
Coming soon to Google Play →Prevention checklist
- Air movement: don’t park plants in dead-air corners; crack a window or run a fan.
- Humidity: stable 40–60%, measured with a cheap hygrometer.
- Hygiene: remove fallen leaves from the soil surface; wipe dusty foliage.
- Inspect new plants before they join the shelf — mildew usually arrives on a newcomer.
- During high-risk weather, a preventive neem or potassium bicarbonate spray on susceptible plants is cheap insurance.
