🥒 Cucumber How hard it is to control: ★★★★★ 5/5

Downy mildew of cucurbits on cucumber

The most dangerous disease in cucumber cultivation, caused by an oomycete (fungal-like organism). Occurs commonly on various cucurbit species both in field and under cover.

Symptom photos

Downy mildew of cucurbits — Leaf — angular yellow patches bounded by veins, turning brown — Leaf — angular yellow patches bounded by veins, turning brown Photo: Christian Hummert ( Ixitixel ), licence CC BY-SA 3.0

Downy mildew of cucurbits — Crop — heavily infected leaves with widespread yellowing of the blade — Crop — heavily infected leaves with widespread yellowing of the blade Photo: Wee Hong, licence CC BY-SA 4.0

Downy mildew of cucurbits — Leaf — mosaic of yellow and green patches at an advanced stage — Leaf — mosaic of yellow and green patches at an advanced stage Photo: Nieznany, licence CC BY-SA 3.0

Downy mildew of cucurbits — Underside of a leaf — browning patches bounded by the vein network — Underside of a leaf — browning patches bounded by the vein network Photo: Nieznany, licence CC BY-SA 3.0

Symptoms

Chlorotic, then yellow and browning irregular spots on upper leaf surface
Gray, then brown-violet coating of stalks and sporangial spores on lower leaf surface
Spots expand and merge covering entire leaf surface
Die-back of entire plants within a few days

What it does to the crop

Very large yield losses
Complete plant die-back
Rapid spreading in cultivation

What encourages it

High air humidity
Frequent rainfall
Long-lasting leaf wetness
Temperature 20-25°C during day and 10-15°C at night
High plant density on plantation

Prevention

Cultivation of resistant or tolerant varieties
Cultivation in open, airy areas, away from water bodies
Avoiding establishing plantations in depressions prone to water accumulation
Weed elimination to increase airiness
Avoiding too dense planting/sowing of plants
Thorough removal of plant debris after cultivation ends

⚠️ 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.

Keep the disease atlas with you in the garden

In the app you can identify a disease from photos, work out the spray dose for your own bed and log the treatment in your task calendar. Free, no sign-up, works offline.

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