Powdery Mildew on Plants: How to Identify, Treat and Prevent It
Powdery mildew looks like someone dusted flour across your leaves. Catching it in the first week keeps it from jumping to every plant in the room.
How to identify powdery mildew
Powdery mildew is a fungal disease caused by several species of fungi in the order Erysiphales. On houseplants and garden plants it shows up as:
- White or pale-grey powdery patches on leaf surfaces — first in small circular spots, then spreading
- Leaves that curl, yellow, and drop as the infection progresses
- Stunted new growth, especially on susceptible plants like cucumber, rose, zinnia, begonia, and African violet
- Worst on plants with poor airflow, in humid rooms, or in crowded plantings
Unlike downy mildew, powdery mildew sits on the leaf surface and can often be wiped off gently with a finger — a quick identification test.
Treatment: the 4-step plan
- Isolate the plant from others immediately. Spores travel on air currents.
- Remove the worst-affected leaves with clean scissors and throw them in the trash — not compost.
- Spray with a simple home mix: 1 teaspoon baking soda + a few drops of liquid dish soap in 1 litre of water. Coat both sides of the leaves.
- Repeat weekly for three weeks, and improve airflow — a small fan on low does more than any spray.
Commercial alternatives
For stubborn infections, neem oil (5 ml/L water) or potassium bicarbonate sprays work well. Skip sulphur sprays on cucurbits (squash, cucumber, melon) — they cause leaf burn.
How to prevent powdery mildew coming back
- Keep humidity below 60% where possible — powdery mildew loves humid, still air
- Space plants so leaves don't touch
- Water at the soil, not the leaves
- Increase airflow with an open window or a small fan
- Choose resistant cultivars if you grow roses, cucumbers, or zinnias outdoors
When to use AI diagnosis
If the white coating looks different from these photos — or there are also brown spots or webbing — it might be downy mildew, botrytis, or spider mites instead. Open the AI Plant Doctor app, snap the affected leaf, and the AI will tell you which pathogen you are dealing with plus the exact treatment.
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