Briosia blight of grape

Briosia blight of grapes is caused by the fungus Briosia ampelophaga, a member of the Hyphomycetes class. This fungal pathogen acts as an obligate parasite, specifically targeting grapevine tissues.

The pathogen colonizes the plant tissues and produces conidiophores on the surface. These structures appear as a velvety, dark-colored mold, which is a diagnostic sign of the infection.

The conidia (spores) of the fungus are multicellular and dark-pigmented. They are highly specialized for dispersal by wind and water splash, allowing the fungus to spread rapidly throughout the vineyard.

The pathogen survives the dormant season as mycelium or spores within plant debris or bark fissures. This ensures its persistence in the vineyard environment from year to year.

As a specialized pathogen, Briosia ampelophaga shows a strong preference for grapevines, making it a persistent challenge for viticulturists in susceptible regions.

The pathogen affects all green parts of the grapevine, including leaves, shoots, tendrils, and inflorescences. Damage to these organs negatively impacts the overall health and vigor of the vine.

Infection of the inflorescences leads to blighting and eventual drop, causing significant yield losses. This reduction in berry set directly impacts the economic productivity of the crop.

Leaves affected by the fungus suffer from necrotic spots that reduce photosynthetic area. This hinders the plant's ability to accumulate sugars, resulting in lower-quality berries at harvest.

Infected shoots exhibit stunted growth and deformation. If the infection is severe, the affected shoots fail to mature properly, making them highly susceptible to winter injury and cold damage.

In epidemic years, Briosia blight can cause substantial destruction of leaf canopy and crop, leading to long-term decline in vine health and weakened stock for the following seasons.

Initial symptoms include the appearance of small, irregular spots on young leaves and shoots. These spots eventually enlarge and turn a dark brown or black color, often with a distinct border.

A dense, olive-brown to black mold layer covers the lesion areas. This layer consists of the fungus's reproductive structures, which continue to release spores under humid conditions.

Lesions on petioles and rachises of clusters often cause constriction of tissues. This disrupts the flow of nutrients, leading to the withering of the cluster and potential abscission of fruits.

Leaves show yellowing followed by browning and premature senescence. This scorched appearance is a classic symptom of advanced infection in highly susceptible vineyards.

While berry infection is less common, the disease can manifest on the skin of developing grapes as dark, scabby spots, which reduces their quality and marketability.

Good viticultural practices are the primary line of defense. Proper canopy management, including thinning and shoot positioning, is essential to improve airflow and reduce humidity within the vine.

Sanitation is critical; all infected plant debris must be removed and destroyed (burned) during the dormant season to eliminate the primary inoculum source for the next cycle.

Fungicide applications are necessary during the growing season to prevent infection. Preventive sprays using copper-based products or systemic fungicides are effective when applied strategically.

Timing is key; early applications before the buds break can significantly reduce the overwintering spore load, limiting the initial pressure of the pathogen on the new growth.

• Regular monitoring of vineyard rows for early signs of lesions.
• Maintenance of balanced soil fertility to promote plant vigor.
• Removal of weeds and ground cover that may increase canopy humidity.