Strawberry powdery mildew

Podosphaera aphanis is a fungus responsible for causing powdery mildew in various plants, with strawberries being the most economically significant host. It is an obligate parasite that derives nutrition directly from living plant cells, which eventually leads to the weakening of the host plant and significant reduction in fruit yield.

The fungus has a broad host range within the Rosaceae family. While strawberry plants are the primary targets, the pathogen can also survive on wild relatives of strawberries and other related species, serving as a reservoir for infection that can spread to cultivated fields via airborne spores during favorable weather conditions.

The primary symptom is the appearance of white, mycelial growth on the underside of leaves. As the disease advances, leaves curl upward, revealing the white fungus and developing reddish or purple margins. When fruit is infected, the berries become stunted, deformed, and covered in a dusty white coating, often resulting in a bitter taste and loss of marketability.

High humidity, warm temperatures, and stagnant air are the primary drivers of Podosphaera aphanis spread. Greenhouses and high tunnels are particularly susceptible due to the lack of air movement and temperature fluctuations that favor sporulation. The pathogen can overwinter in dormant foliage or as specialized resting structures called chasmothecia on decaying debris.

Effective management requires a combination of cultural and chemical control strategies. Cultural practices include selecting resistant cultivars, maintaining wide spacing to facilitate air circulation, and rigorous sanitation by removing infected plant parts. Chemical control, involving sulfur-based products or systemic fungicides, is essential during peak disease periods, ensuring appropriate safety intervals are respected prior to harvest.

• Planting resistant or tolerant strawberry varieties.
• Implementing efficient irrigation systems to keep foliage dry.
• Sanitizing tools and equipment to prevent cross-contamination.
• Monitoring environmental parameters within greenhouses.
• Applying fungicides based on integrated pest management (IPM) guidelines.