Powdery Mildew Is Covering My Strawberry Leaves

A white or off-white powdery coating on the upper and lower surfaces of strawberry leaves — and sometimes on developing fruits — is strawberry powdery mildew, caused by the fungus Podosphaera aphanis. Unlike most fungal diseases, powdery mildew thrives in warm, dry conditions rather than wet ones, making it most common in sheltered beds and under polytunnels in summer. Infected leaves often curl upward at the edges, exposing the white powdery underside, and fruits may develop a powdery coating that makes them unpalatable.

Why powdery mildew appears

Podosphaera aphanis spores germinate and spread in warm, dry conditions with moderate to high air humidity. The fungus grows entirely on the leaf surface, extracting nutrients without needing free water for spore germination (unlike downy mildew or Botrytis). Plants under cover in polytunnels or greenhouses, with poor air circulation and warm temperatures, are most susceptible. Crowded beds with dense leaf coverage where air movement is reduced also favour the disease. Drought stress in open beds weakens plants and makes them less resistant.

Affected fruit — is it safe to eat?

Strawberries with a powdery mildew coating on the surface are safe to eat after washing, though the texture and flavour may be somewhat compromised. The white coating itself is fungal mycelium on the surface and washes off. However, severely affected fruits are often smaller and less flavourful due to the stress placed on the plant, and the appearance makes them unappetising. The priority is preventing severe fruit infection through good management rather than salvaging badly affected crops.

Management

Improve air circulation around plants by removing excess runners and dead leaves, and by not planting too closely. Water the soil (not the leaves) in the morning so leaves dry quickly — although powdery mildew does not need wet leaves to spread, free moisture on leaves can contribute to overall plant stress. Potassium bicarbonate or baking soda (sodium bicarbonate) solutions applied as a spray create an alkaline surface environment that kills powdery mildew spores on contact — safe for organic growing and effective when applied at first sign of infection. Choose mildew-resistant varieties (Elsanta, Cambridge Favourite) for future plantings if mildew is a persistent problem on your site.