Anthracnose, black spot, bird`s eye rot, bird`s eye spot is found worldwide. The disease reduce fruit quality and yield, weaken the vine via significant destruction of new shoots and leaves. Most Vitis species are susceptible to anthracnose.
In humid grape vine growing seasons the diseas is well established, it causes damages to highly susceptible cultivars following early season rains.
Once established in vineyards, the disease can be very difficult to manage. However in Euorpe the disease is nearly negligible because of fungicides with copper compounds, dithiocarbamates, phthalimids to control downy mildew and the lack of rainfall in the arid climates.
The disease attack the aerial, succulent parts of the vine, including young soots, leaves, petioles, tendrils and clusters; lesions on shoots and berries are most common.
First symptoms appear as isolated, small, circular spots which become brownish, sunken with gray centes and dark, round or angular margins. Sometimes symptoms look like hail injury. On leaves numerous small, brown spots appear, which are gray in the centre, the necrotic centre usually drops out, creating a "shot- hole" appearance.
Young leaves are more susceptible for infections.
On berries small reddish- brown, circular spots develop,which become slightly sunken. The centre turns grey and will be surrounded by reddish- brown to black margins (bird`s eye).
Life cycle of the pathogen
The disease is caused by the pathogen Elsinöe ampelina (de Bary) Shear.
Infected canes are the mail source of the disease. Sclerotia or mycelium surviving in the lesions become active in spring and produce conidia under wet conditions (rain or dew for 24hours) within temperature regime of 2°C-40°C. The conidia are splashed by rain to new tissue. They germinate and produce new infections.
Warm weather reduce the wetting time needed for initial infection and the incubation periode before symptoms are visible on the leaves.
Optimum spore germination occurs at 25-30°C, with a minimum of 3- 4 hours of requiered leaf wetness. Also the incubation time is shortest within this temperature range (3-4 days under ideally wet conditions). At infections at at temperature around 10°C, disease symptoms need abou 14 days to be visible on leaves.
Conidia or ascospores formed on infected berries that overwinter on the vine or floor may also cause primary infections.
Spores infect new leaves, shoots, tendrils, young berries and produce lesions at humid conditions. These conidia serve as secondary inoculum and are responsible for further infections in the season. The conidia are disloged by raindrops and dispersed in the vineyard.
Epidemic development is caused by susceptibility of the grapevine tissue, dispersal of conidia, and prevailing weather conditions. The most important factor is the frequency of rainy periods.
Modelling in Fieldclimate.com
Overwintering spores development: Temperature: 2-40°, relative humidity above 90% or leaf wetness- when spores are developed (100%) and still conditions of leaf wetness and temperature infection starts to be calculated.
Spore development (lower 50% r.h.) and Infection stopps when humidity is too low. Severity of infection depends on the wet conditions (rain event)