Pleurostoma trunk disease

Typical signs of Pleurostoma trunk disease include internal wood necrosis observed as dark or black streaking in the heartwood when the trunk or cordons are cross-sectioned.

Externally, infected vines exhibit reduced vigor, shortened shoot growth, and leaves that may show chlorosis or necrotic margins. These symptoms often progress slowly over several years.

Affected arms or cordons may show sudden dieback, especially during periods of water stress, as the compromised vascular system cannot sustain the water demands of the foliage.

Crop yields gradually decline as the disease spreads through the wood, resulting in smaller clusters and lower quality berries that fail to mature properly.

• Internal wood discoloration
• Reduced plant vigor
• Stunted shoot growth
• Cordon dieback

The causal agent of this condition is the ascomycete fungus Pleurostoma richardsiae. It is a significant pathogen involved in the complex of grapevine trunk diseases (GTDs).

The fungus colonizes the xylem vessels of the vine. By growing within the vascular system, it causes obstruction that leads to the typical symptoms of wood necrosis and eventual plant decline.

Propagation of the pathogen occurs mainly through conidia, which are disseminated by rain splash and wind. It persists in infected wood, making the orchard a long-term reservoir for the disease.

Biological studies indicate that the fungus can remain dormant within the vine for years before symptoms become visible, which complicates early detection in vineyards.

Its role as an endophyte allows the fungus to establish itself deep within the perennial wood structure, making it difficult to reach with standard surface-applied treatments.

The infection is largely facilitated by pruning wounds. Spores land on fresh cuts, germinate, and penetrate the wood tissue, establishing the initial infection site.

Environmental conditions such as rainfall during the pruning season significantly increase the risk of disease transmission by facilitating the release and dispersal of conidia.

Vines under environmental stress, such as drought or extreme temperature fluctuations, are more susceptible to colonization by the pathogen due to weakened host defenses.

The use of unsterilized pruning tools is a critical factor in the horizontal spread of the fungus within the vineyard, as tools can transfer spores from infected to healthy vines.

The presence of old wounds or previously damaged wood provides suitable niches for the fungus to establish its presence and accumulate inoculum in the vineyard.

The primary harm is the destruction of the vine's conductive tissue, which leads to slow, progressive death of the plant. This causes significant financial loss to growers.

As a chronic disease, it shortens the productive lifespan of the vineyard, requiring premature replanting of entire vineyard blocks, which is a major economic burden.

The disease reduces both the quantity and quality of the harvest, as the vine cannot effectively transport the nutrients necessary for optimal berry development.

There is a high risk of systemic infection within the vineyard, as spores are dispersed by wind and rain, potentially affecting a large portion of the acreage over time.

Because the disease is often systemic and hidden within the wood, it is difficult to identify until substantial damage has already occurred, limiting management options.

Rigorous sanitation during pruning is the most effective prevention strategy. Tools must be disinfected frequently to prevent the transmission of the fungal pathogen between vines.

Applying wound-protectant sealants or fungicides to fresh pruning wounds helps prevent spores from entering the wood, which is crucial for younger, vulnerable vines.

Removing and burning symptomatic wood is recommended to reduce the overall inoculum load in the vineyard, though it may not stop existing infections in the trunk.

While there are currently no curative treatments for infected trunks, managing vine health through proper irrigation and nutrition can help prolong the life of affected plants.

Choosing healthy, disease-free nursery stock is the foundation for avoiding this disease, as it prevents the introduction of the pathogen into new planting areas.