Powdery Mildew
Erysiphales
White powdery fungal growth on leaves. Worst on cucurbits, peas and brassicas in warm dry weather with cool nights.
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Identify from a photoBackground
Powdery mildew is a group of related fungi that infect leaves, stems and sometimes fruit. Unlike most fungal diseases it thrives in relatively dry conditions with high dew formation overnight. Infection reduces photosynthesis, weakens the plant and exposes fruit (on cucurbits in particular) to sunscald once leaves shrivel.
Different powdery mildew species infect different crop families, but the management is broadly similar.
How to identify
- White or pale grey powdery patches on leaf upper surfaces, spreading to cover whole leaves
- Leaves later yellow, curl and die
- On cucurbits, starts on older shaded leaves and moves upward
- On peas, starts on older lower leaves; whole plant can be coated within a fortnight
Life cycle
Spores airborne, germinate on leaf surfaces in 6-8 hours of high humidity even without free water. Infection to new spore production in 4-7 days.
Weather triggers
- Temperature: 15-30°C
- Humidity: >60%
- Paradoxically worst in warm dry days with cool humid nights. Heavy rain washes spores off but keeps leaves wet long enough for some infection.
Peak season (southern hemisphere)
Red = active season · Dark red outlined = this month
Affected vegetables & crops
Click any crop to see current prices and growing info.
Climate zones at risk
Organic & low-impact control
- Potassium bicarbonate or sodium bicarbonate sprays (eg Eco-Carb) at first sign
- Milk spray diluted 1:9 with water, weekly (traditional home remedy, documented efficacy)
- Sulphur sprays. Effective but avoid on cucurbits in hot weather (>30C) due to phytotoxicity
- Remove and bag affected leaves
Chemical control
- Wettable sulphur is the most common home garden option
- Commercial systemic fungicides (myclobutanil) are registered for some crops but rotate modes of action to avoid resistance
Always read product labels. Registrations change.
Prevention
- Plant in full sun with good airflow
- Space plants generously; train cucurbits on a frame
- Water at the root zone. Avoid wetting foliage in the evening
- Choose resistant cultivars where available
Companion planting
No companion plant reliably prevents powdery mildew. Understorey plantings that retain humidity (e.g. dense ground covers) can actually worsen it.
Biosecurity
Cosmopolitan fungi. No quarantine concerns.
Know when Powdery Mildew is actually about
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