Black rot (grape disease)

Guignardia bidwellii 04

Black rot is a fungal disease that affects grapevines, caused by the pathogen Guignardia bidwellii. This disease is a significant concern for viticulturists as it can lead to severe crop losses if not managed properly.

Symptoms

The symptoms of black rot appear on all green parts of the grapevine, including leaves, shoots, and fruit. On leaves, the disease manifests as small, circular, reddish-brown spots with black borders. As the disease progresses, the spots enlarge and develop black, pimple-like structures called pycnidia, which are the fruiting bodies of the fungus. Infected shoots exhibit elongated, sunken lesions, while infected berries shrivel and turn black, becoming mummified.

Disease Cycle

The black rot fungus overwinters in mummified berries and infected canes. In the spring, during wet weather, the fungus produces spores that are dispersed by rain splash to new growth. Infection occurs when the spores land on susceptible tissue and conditions are favorable, typically warm and wet weather. The fungus then penetrates the plant tissue, leading to the development of symptoms.

Management

Effective management of black rot involves a combination of cultural practices and chemical control. Key strategies include:

• **Sanitation**: Removing and destroying mummified berries and infected canes during the dormant season to reduce the source of inoculum.
• **Pruning**: Proper pruning to improve air circulation and reduce humidity within the canopy.
• **Fungicide Applications**: Applying fungicides at critical times, particularly during the early growing season when new growth is most susceptible.

Related Pages

• Grape
• Fungal diseases of plants
• Viticulture
• Plant pathology