Phaeoacremonium decline

Visual symptoms often manifest as stunted growth, shortened internodes, and smaller, chlorotic leaves that may develop necrotic spots over time.

A diagnostic sign upon cross-sectioning the trunk or cordons is the presence of dark, necrotic streaks within the wood. These streaks indicate colonized vessels where the fungus has compromised the plant's vascular network.

During the peak of the growing season, vines may display "apoplexy" or sudden wilting. Affected canes or entire cordons may dry out rapidly, especially under high heat stress, with leaves curling and turning brown.

Reduced berry set, irregular cluster maturation, and overall decline in yield are common outcomes. Grapes may lack sugar content and flavor, significantly impacting the quality of the harvest.

Over several seasons, the affected parts of the vine become brittle and necrotic, often leading to the eventual death of the affected arm or the entire plant.

The disease is caused by the fungus Phaeoacremonium italicum, a member of the Ascomycota division. This pathogen is one of several species responsible for the complex of grapevine trunk diseases (GTDs).

The fungus is a vascular pathogen capable of colonizing the xylem vessels of the grapevine. Once inside, it secretes enzymes that break down the woody tissue, eventually leading to a loss of structural integrity and water transport capacity.

Phaeoacremonium italicum can survive as an endophyte within the vine for extended periods without showing visible symptoms, making it a latent and persistent threat in vineyard environments.

Spore dispersal occurs primarily through rain-splash and wind. The pathogen thrives by infecting open wounds, particularly those created by pruning or winter damage, where spores land and germinate.

Research indicates that this fungus is frequently found in mixed infections alongside other trunk disease pathogens like Phaeoacremonium minimum, which complicates identification and management strategies.

Pruning is the most critical period for infection. Conducting pruning activities during wet, rainy weather facilitates the release and transport of fungal spores directly onto fresh pruning wounds.

Mechanical injuries resulting from frost damage, hail, or agricultural equipment provide entry points for the pathogen. Vines that are stressed or improperly managed are significantly more vulnerable.

The development of the fungus within the vine is favored by warm temperatures, typically ranging from 20°C to 28°C. These conditions coincide with the active growth phase of the vine, allowing the pathogen to colonize new tissue efficiently.

Poor site sanitation is a major risk factor. Keeping infected prunings or dead vines in the vineyard allows the fungus to continue sporulating and infecting neighboring healthy vines.

High plant density and lack of adequate nutrition can exacerbate the spread, as these factors contribute to overall plant stress, making them less capable of resisting the fungal colonization.

The disease is progressive and generally irreversible. Once the fungus has colonized the permanent wood, systemic treatment is currently not effective, leading to the necessary removal of affected sections.

The economic impact is profound, resulting in high mortality rates for vines, increased labor costs for replacement, and significant loss of revenue due to reduced yield and poor fruit quality.

Vineyard longevity is drastically reduced. Instead of a lifespan of several decades, heavily affected vineyards may become unproductive or require total replanting within a few years of initial symptoms.

The pathogen severely limits the vine's ability to cope with environmental stresses like drought or heat, further accelerating the decline and eventual collapse of the vineyard.

Management expenses increase annually due to the need for strict sanitation protocols, specialized labor for wood removal, and continuous monitoring of the health of the entire block.

Prevention is the only viable management strategy. Growers should prioritize the purchase of certified, pathogen-free nursery stock to avoid introducing the disease to new planting sites.

All pruning wounds should be treated with protective sealants or fungicides to create a physical barrier against spore infiltration. Reducing the size of pruning cuts is also recommended.

Rigorous tool sanitation is mandatory. Pruning shears and saws must be disinfected after each vine with 70% ethanol or a bleach solution to prevent the mechanical transmission of spores.

• Regular inspection and marking of symptomatic vines during the growing season.
• Removal and destruction of heavily infected wood through burning.
• Avoidance of pruning during rainy weather conditions.
• Promoting vine vigor through balanced irrigation and nutrient management.

Since no chemical cure exists for infected wood, successful control relies heavily on early detection, maintaining high sanitation standards, and ensuring that no infected material remains in the field.