Powdery Mildew in Cucumber — Identification, Prevention & Management

Powdery mildew is one of the most common and economically damaging fungal diseases in cucumber cultivation — especially in polyhouse conditions. Caused primarily by Sphaerotheca fuliginea and Erysiphe cichoracearum, it can reduce yield by 20–40% if not managed early.

How to Identify Powdery Mildew

Look for white or grey powdery patches on the upper surface of leaves, starting with older leaves near the base of the plant. The patches spread rapidly across the leaf blade, eventually causing yellowing and premature leaf drop. Unlike downy mildew, the patches are on the upper leaf surface and do not have a watery appearance.

Conditions That Trigger Spread

• High humidity combined with warm daytime temperatures (25–30°C)
• Low air circulation within polyhouse — especially closed structures in winter
• Water stress (underwatering or overwatering cycles)
• Dense planting with insufficient pruning of older foliage
• Sudden temperature fluctuations (warm days, cool nights)

Prevention — Your First Line of Defence

Choose disease-resistant varieties. Our Yasemin F1 carries IR: CGMMV resistance. Kaveri F1, Veda F1, Deepti F1, and Terminator++ F1 all carry IR: CYSDV, ZYMV resistance packages that reduce susceptibility.

Maintain relative humidity below 85% inside your polyhouse. Open side vents during morning hours. Remove lower leaves up to node 10 as the crop progresses to improve air circulation.

Chemical Management

Begin spray programme when first symptoms are observed — do not wait. Rotate between fungicide groups to prevent resistance:

• Sulphur WDG 80% — 2.5 g/litre (preventive and curative, cheap and effective)
• Hexaconazole 5% EC — 1 ml/litre (systemic, curative)
• Trifloxystrobin + Tebuconazole — 0.5 g/litre (premium, systemic)
• Azoxystrobin 23% SC — 1 ml/litre (preventive, very effective early-stage)

Organic Management Options

Neem oil spray (5 ml/litre + emulsifier) applied every 7 days as a preventive measure. Potassium bicarbonate (5–8 g/litre) is effective as an organic curative option. Both work best when applied before infection becomes severe.