Powdery mildew
A white, flour-like coating that spreads over leaves, shoots and pods — and, unusually for a fungus, thrives in dry weather with cool nights.
- Pathogen
- Fungus (Erysiphales)
- Spreads by
- Wind-blown spores
- Favoured by
- Dry days, cool humid nights
- Main risk
- Dried leaves; shrivelled grain/fruit
Overview
Powdery mildew is a very common fungal disease that shows as a white to greyish, powdery, flour-like growth, usually first on the upper surface of the leaves and on tender shoots, buds and pods. As it spreads it can cover much of the plant; the affected leaves yellow, curl and dry, and grain, pods or fruit fill poorly and shrivel.
Different (but related) powdery-mildew fungi attack wheat, peas, cucurbits, grapes, mango, mustard and many pulses — each fairly host-specific, but all behaving the same way. Unusually for a fungal disease, powdery mildew does NOT need leaf wetness: it thrives in warm, dry days with cool, humid nights, and even in dry weather, which is why it can flare when other diseases do not. It is favoured by dense, shaded, over-fertilised (high-nitrogen) crops.
How to identify it
- White to greyish, powdery, flour-like patches on the upper surface of leaves, and on shoots, buds and pods.
- Patches that enlarge and merge to coat much of the leaf and plant; the powder can be rubbed off with a finger.
- Affected leaves yellow, curl, dry and fall; grain, pods or fruit fill poorly and shrivel.
- On grapes and mango, powdery growth on the flower clusters and young fruit that cracks and drops.
What causes it and when
- Powdery-mildew fungi (Erysiphales), spread by wind-blown spores — no rain or leaf wetness is needed for infection.
- Favoured by warm, dry days with cool, humid nights, and by dense, shaded, poorly-ventilated crops.
- Worsened by excess nitrogen, which produces the soft lush growth the fungus prefers.
- Different host-specific species affect cereals, pulses, cucurbits, grapes, mango and mustard, but management is similar.
Cultural & organic control
- Grow resistant/tolerant varieties where available, and give open spacing and good ventilation so the canopy dries and airs.
- Avoid excess nitrogen; balanced nutrition makes the crop less susceptible.
- Spray wettable sulphur — the classic, effective and low-cost control for powdery mildew — or a recommended bio-agent, at the first sign.
- Remove and destroy heavily-affected leaves/shoots, and destroy crop residue after harvest.
Chemical control
- Act at the first white patches — powdery mildew is far easier to stop early than after it coats the crop.
- Wettable sulphur is the first-line fungicide; where more is needed, CIB&RC-registered systemic fungicides for the crop (e.g. triazoles) are used and rotated to avoid resistance.
- Get good coverage of the upper leaf surface where the fungus grows, and observe the pre-harvest interval, especially on grapes and vegetables.
- Do not use sulphur in very hot weather or on sulphur-sensitive varieties (some cucurbits/grapes); follow the label.
Prevent it coming back
- Choose resistant varieties and avoid dense, over-shaded, over-fertilised planting.
- Scout during dry spells with cool nights — the classic powdery-mildew weather — and act early.
- Rotate fungicide groups and lean on sulphur and cultural measures so the fungus does not build resistance.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My leaves have a white powdery coating that rubs off. What is it?
That white, flour-like coating on the upper leaf surface (and on shoots and pods) that rubs off with a finger is powdery mildew, a fungal disease. It spreads over the plant, yellows and dries the leaves, and shrivels grain or fruit. Spray wettable sulphur at the first sign, improve airflow, and avoid excess nitrogen.
Why does powdery mildew appear even in dry weather?
Unlike most fungal diseases, powdery mildew does not need rain or leaf wetness to infect — it thrives in warm, dry days with cool, humid nights. That is why it can flare in dry spells when other diseases are absent. Dense, shaded, over-fertilised crops make it worse. Sulphur sprays and good spacing keep it in check.
What is the cheapest effective control?
Wettable sulphur is the classic, cheap and effective fungicide for powdery mildew, especially applied at the first white patches. Combine it with resistant varieties, open spacing, good ventilation and avoiding excess nitrogen. Avoid sulphur in very hot weather or on sulphur-sensitive varieties, and reserve stronger systemic fungicides (rotated) for heavy pressure.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.