Macrophoma leaf spot

The fungus Macrophoma flaccida is the primary pathogen responsible for a specific type of necroses and leaf spots on grapevines. This disease primarily affects the woody parts and foliage of the plant. It is considered a latent pathogen that can persist in the tissue for extended periods before manifesting visible symptoms.

Grapevines are the main host for this pathogen. While it may infect various parts of the plant, its impact is most severe on the canes, where it disrupts the vascular tissues. It is widely distributed in vineyards where moisture levels are high and canopy management is neglected, leading to poor air circulation.

Symptoms appear as light-colored spots on the shoots, which eventually darken and turn into necrotic lesions. As the infection progresses, the bark on the affected canes may peel, revealing the characteristic small black pycnidia of the fungus. Infected leaves often show chlorotic lesions, which can lead to premature leaf drop during the summer.

The development of the fungus is favored by extended periods of high humidity, frequent rainfall, and moderate temperatures. The spores are primarily disseminated by water splash and wind, entering the host through pruning wounds, insect injuries, or natural cracks in the bark during the growing season.

• Implement strict sanitation practices by pruning and destroying infected wood.
• Apply copper-based fungicides or other recommended sprays during dormant and active stages.
• Maintain proper vine spacing and canopy management to enhance airflow.
• Disinfect pruning equipment regularly to avoid cross-contamination of healthy vines.
• Ensure adequate vine vigor through balanced fertilization to improve plant defense.

The economic impact of Macrophoma flaccida includes reduced yields, stunted growth, and the dieback of entire arms or canes. If left unmanaged, the pathogen significantly weakens the vine, shortening its productive lifespan and potentially leading to the loss of entire plants in severely infested vineyard blocks.