Powdery mildew of grapevine

Powdery mildew, caused by the fungus Uncinula necator (often referred to as Erysiphe necator), is one of the most destructive diseases affecting grapevine cultivation worldwide. It is an obligate biotrophic pathogen belonging to the Erysiphales order that thrives on all green tissues of the Vitis species.

The disease is characterized by the appearance of a white, dusty fungal growth on leaves, shoots, inflorescences, and berries. As the infection progresses, the mycelium covers the surface of the fruit, causing the skin to harden and eventually burst. This damage not only ruins the harvest quality but also makes the plant highly susceptible to secondary infections, such as bunch rot.

The fungus survives the winter primarily as mycelium within dormant buds or as cleistothecia embedded in the bark of the vine. When temperatures rise in the spring, the fungus resumes growth, producing asexual spores called conidia. These spores are dispersed by wind and splashing rain, initiating a rapid cycle of secondary infections throughout the growing season.

Optimal environmental conditions for the development of Uncinula necator include temperatures between 20°C and 25°C. Unlike many other fungal pathogens, powdery mildew does not require free water or high humidity for germination; in fact, high humidity can sometimes suppress its development. This adaptability allows the fungus to spread rapidly during warm, dry summers.

Integrated management is essential for controlling this pathogen effectively. Key strategies include:

• Canopy management to improve airflow and sunlight penetration within the vine foliage.
• Application of fungicides, specifically sulfur, triazoles, and strobilurins, during high-risk phenological stages.
• Strict monitoring of the vineyard to initiate chemical control at the very first signs of infection to prevent exponential spore production.