Anthracnose, also known as bird's-eye rot, is a fungal disease. When uncontrolled, it can reduce both fruit quality and fruit yield. The fruiting bodies, or sclerotia, overwinters in vineyards on the infected tissue, which when exposed to conducive conditions in the spring, become active and produce conidia. Mature conidia are then splashed onto new grape tissue, where the conidia germinate resulting in infection. These infections result in reduced fruit quality and reduced yield. Most grape varieties are susceptible to Anthracnose, but once the fruit reaches maturity, they become less susceptible.
Signs and Symptoms
|Brown spots on leaf surface|
|Brown spots on stem|
Leaves develop numerous circular brown spots which later turn gray in the center with dark brown or black margins. In older lesions, necrotic centers may fall out giving a tattered appearance (image on the right, Photo courtesy- Michigan State University).
Shoots develop small oval shaped, purplish-brown spots. The spots have raised edges and as the disease progresses the spots enlarge into brownish sunken lesions with dark round or angular margins (image on the right, Photo courtesy- The Ohio State University).
Berries initially develop small purplish-brown spots which then enlarge into purplish-black spots with a lighter center, giving it a distinctive appearance of a bird’s eye. Lesions may extend to the pulp which then induces cracking and can facilitate secondary infections.
Anthracnose Disease Management
The primary inoculum for the following year is found on infected tissue in the vineyards. This makes sanitation a very important step towards maintaining an Anthracnose free vineyard.
- Diseased canes should be pruned during the dormant season and then be removed from vineyards or destroyed.
- Spores produced from infected berries that are left on the vineyard floors can be reduced from causing next seasons infections by covering the infected berries with soil or mulch.
- Wild grapes found near the vineyard should be removed to further reduce sources of inoculum for next season's primary infections.
Fungicides should be applied shortly before bud break. Commercial growers should consult the current year’s release of the Midwest Fruit Pest Management Guide for up to date fungicide recommendations.
Management of the vineyard canopy is a very important practice. Trailing shoots should be removed or properly trained to facilitate better air circulation. Avoid susceptible varieties in areas with heavy soils and poor drainage. To maintain a healthy plant follow good growing practices, more information can be found at Midwest Grape Production Guide.
Currently, there are no bio-control products available that are effective against Anthracnose.