Downy mildew on zucchini
Pseudoperonospora cubensis infects courgette leaves from the second half of July. On the upper surface it gives angular yellow patches boxed in by the veins, with a delicate grey-violet growth underneath.
Symptom photos
Symptoms
- Angular yellow patches boxed in by the leaf veins
- A delicate grey-violet growth on the underside of the patches
- Patches browning and drying, then whole leaves following
- Symptoms working up from the oldest leaves
- Dried leaves curling upwards
What it does to the crop
- Rapid leaf loss and cropping cut short
- Small, poorly colored fruit exposed to sunscald
- The picking season shortened by several weeks
- Plants dying where the attack is severe
What encourages it
- High humidity and long-lasting dew
- Temperature 15-23°C with frequent rain
- A crowded, poorly ventilated crop
- Spores blown in on the wind, even from a long way off
Prevention
- Space plants widely on an airy site
- Drip-irrigate in the morning without wetting the leaves
- Remove the first affected leaves
- Grow tolerant varieties
- Clear crop debris after harvest
⚠️ 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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