Powdery mildew

Powdery mildew, caused by the fungus Erysiphe necator, is one of the most persistent and damaging diseases in viticulture globally. This obligate biotroph develops mycelium on the surface of green plant tissues, feeding through specialized structures called haustoria that penetrate the epidermal cells of the host.

The disease primarily attacks grapevines, including both table and wine varieties. Every green part of the vine is susceptible, including young shoots, leaves, flowers, and developing berries. Early season infections on shoots and inflorescences are particularly detrimental to plant vigor and productivity.

The key symptom of Erysiphe necator is a white or gray powdery growth that can cover any green surface. As the infection progresses, leaves may curl and stunt, while affected berries often stop growing, split open, and fail to ripen properly. In severe cases, the infected clusters emit a distinct, musty odor.

The development of this pathogen is favored by warm, humid conditions. Ideal temperatures range between 20°C and 27°C. Unlike many other fungal pathogens, Erysiphe necator does not require free water or rain to spread; high atmospheric humidity is sufficient for conidia germination and colonization.

The economic impact of powdery mildew is significant, leading to reduced yields and inferior wine quality due to damaged skins and compromised sugar content. Effective management strategies are essential to maintain vineyard health:

• Canopy management practices such as pruning, thinning, and leaf removal to improve air circulation.
• Application of sulfur-based fungicides as a preventative measure.
• Rotation of systemic fungicides to prevent the development of resistant pathogen strains.
• Removal and destruction of infected canes during winter pruning to reduce the primary inoculum load.