Alternaria leaf spot of grapevine

Pathogen and disease type. Alternaria leaf spot is a fungal disease caused by the pathogen Alternaria vitis. It belongs to a group of necrotrophic fungi that aggressively invade plant tissues, taking advantage of favorable environmental conditions to proliferate and cause widespread cellular damage in susceptible grapevines.

Affected crops. The disease primarily affects grapevine varieties (Vitis vinifera and hybrids). While it can attack vines of all ages, it is particularly prevalent in vineyards with insufficient airflow, high humidity levels, and poor canopy management, which allow the fungus to establish itself more easily.

Symptoms and signs of damage. Early stages of infection appear as small, light brown, or gray lesions on leaves, often surrounded by a darker border. As the fungal colony expands, these lesions may merge, eventually developing a distinct olive-green or grayish, velvety appearance due to the formation of abundant spores. Fruit clusters may also show dark, sunken lesions, leading to shriveling and decay.

Conditions for development and spread. The development of Alternaria vitis is heavily dependent on high moisture levels and warm temperatures, typically between 20°C and 30°C. The pathogen survives the winter as mycelium within bark crevices, infected canes, or plant debris on the soil surface. Spores are then dispersed by wind, rain splashes, and vineyard equipment to neighboring healthy tissues.

Harmfulness and protection measures. This disease causes significant economic loss by reducing photosynthetic capacity through premature defoliation and directly spoiling bunches. Controlling the disease requires a combination of strict cultural practices and chemical intervention.

• Sanitize the vineyard by removing and burning infected pruning residues.
• Improve canopy ventilation through proper shoot thinning and leaf removal.
• Apply preventative fungicide sprays before infection periods peak.
• Monitor vine health and ensure balanced fertilization to reduce plant stress.