Powdery mildew

Powdery mildew is a destructive plant disease caused by the ascomycete fungus Erysiphe necator. It is classified within the Erysiphaceae family and acts as an obligate parasite, drawing nutrients directly from the epidermis cells of its host plant. While it affects various crops, it is most notorious as a primary pathogen in viticulture.

The disease symptoms typically appear as white or greyish powdery fungal growth on the leaves, shoots, and fruit clusters. Unlike many other fungal pathogens, the mycelium of powdery mildew remains largely on the surface of the plant tissue, sending small suckers called haustoria into the plant cells to extract nutrients, which leads to necrosis and tissue malformation.

The life cycle begins with the fungus overwintering as mycelium in dormant buds or as chasmothecia on the bark. In spring, when temperatures rise, primary infections occur. Conidia (asexual spores) are produced in massive quantities and spread via wind. These spores do not require liquid water to germinate, allowing them to spread rapidly in humid air conditions.

Environmental conditions that favor powdery mildew include temperatures between 20°C and 27°C. High humidity levels, combined with stagnant air caused by poor canopy management, create the perfect microclimate for an outbreak. Plants suffering from excessive nitrogen fertilization are often more susceptible to infection due to the production of softer, succulent tissue.

Effective management requires an integrated approach. Cultural practices such as leaf pulling, shoot thinning, and canopy management are crucial to ensure airflow and light penetration. Chemical control strategies include:

• Sulfur-based fungicides (contact action).
• Triazole-based systemic fungicides.
• Strobilurin fungicides.
• Biological control agents, such as specialized bacteria or fungi.