Rust on onion
A fungal disease (Puccinia allii) producing orange, powdery spore pustules on the leaves. It most often appears on garlic and leeks, but in wet summers it attacks onions too.
Symptom photos
Symptoms
- Orange, raised spore pustules bursting through the leaf surface
- Pale yellowish flecks preceding the spore burst
- Dark brown spore pustules later in the season
- Leaves yellowing and drying from the tip
- Orange dust on your hands after touching the leaves
What it does to the crop
- Leaves drying off early and smaller bulbs
- Yield down by as much as half in a heavy attack
- Poorer keeping quality
- Rapid spread to garlic and leeks
What encourages it
- High humidity and long-lasting dew
- Temperature 10-20°C
- Too much nitrogen
- Alliums grown next to and after one another
Prevention
- Rotate with a 3-4 year break for alliums
- Keep wide spacing so air moves through the crop
- Feed nitrogen moderately and potassium adequately
- Remove and destroy infected leaves
- Water in the morning, not wetting the leaves in the evening
⚠️ Before you reach for a spray
This atlas is informational and still growing — different diseases can look almost identical. Confirm the diagnosis and read the product label before applying any plant protection product. If you are unsure, ask your local extension or advisory service.
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