Bunch stem

Bunch stem, widely known as bunch stem necrosis, is a serious physiological disorder affecting grapevines. It manifests as the rapid dying of the rachis tissue, which essentially cuts off the flow of nutrients and water to the grape clusters, leading to withered fruit and significant yield losses.

This condition is considered a physiological dysfunction rather than a classic infection caused by a single organism. However, it often involves secondary pathogens that exploit the weakened rachis. It primarily affects the Vitis vinifera species during the period of berry development and ripening, causing severe economic impact.

The biology of this disorder is centered on the disruption of the vascular system within the rachis. Studies indicate that an imbalance in mineral uptake, particularly potassium, magnesium, and calcium, plays a critical role. When the plant is under metabolic stress, the rachis tissue cells die, leading to the collapse of the cluster structure.

Environmental conditions trigger this disorder significantly. Key factors include extreme temperature fluctuations, such as cold nights combined with high humidity during the day, as well as excessive soil moisture or severe drought. Poor ventilation within the vine canopy is also a known contributor to the development of necrotic lesions.

• Monitor soil mineral levels regularly.
• Apply magnesium and calcium foliar sprays.
• Ensure proper vine spacing and canopy management.
• Avoid excessive nitrogen fertilization during late growth stages.
• Prune to improve airflow throughout the foliage.

Effective management requires a comprehensive approach to vineyard health. By maintaining balanced nutrition and implementing proper pruning techniques to allow adequate light and air penetration, growers can significantly reduce the risk of bunch stem necrosis. Consistent monitoring throughout the growing season is essential for early detection and mitigation.