Phaeomoniella leaf spot

Phaeomoniellaceae is a family of fungi associated with serious wood decay in grapevines, most notably the species Phaeomoniella chlamydospora. This pathogen is a primary causative agent of Petri disease, which is part of the complex group of grapevine trunk diseases (GTDs). The fungus colonizes the xylem vessels of the vine, causing significant disruption to water and nutrient transport.

The primary host for this pathogen is the cultivated grapevine (Vitis vinifera). The disease affects all stages of development, from young nursery grafts to mature, high-yielding vines. It is a chronic infection that often remains asymptomatic for years, making early detection and nursery management critical for long-term vineyard health.

Symptoms often manifest as stunted growth, shortened internodes, and foliage chlorosis. In advanced stages, leaves may show marginal necrosis. A diagnostic feature is the presence of brown or black streaks and spots in the woody tissue when the trunk or cordons are cross-sectioned. These necrotic lesions are a direct result of the fungal colonization of the vascular tissue.

The spread of the disease is predominantly associated with anthropogenic activity, particularly pruning. Spores are dispersed by rain and wind and can settle on fresh pruning wounds. Once inside the vine, the fungus grows slowly, gradually increasing the severity of vascular blockages. Environmental stress factors, such as drought or poor site selection, can exacerbate the impact of the disease.

Managing Phaeomoniella infections is notoriously difficult once the fungus is established, emphasizing the necessity of preventive measures:

• Sourcing certified disease-free nursery stock.
• Strict sanitation protocols for pruning shears and saws.
• Application of protective wound sealants immediately after pruning.
• Monitoring vineyards for early signs of decline and vigour loss.
• Removing and incinerating vine wood showing significant wood necrosis.