Background
Black spot or anthracnose of grapevines is caused by the fungus Elsinoe ampelina. The disease is found worldwide where grapes are grown, including Western Australia. It can be particularly damaging in regions that experience cool, wet springs and is often more of a problem for table grape varieties such as sultana and red globe. It can reduce fruit yield and quality.
The introduction of fungicides to prevent the disease has reduced its impact. In Western Australia, the disease can appear when spring rainfall occurs and control measures have not been used or have been used incorrectly.
Symptoms
The disease produces characteristic symptoms on leaves and shoots, particularly in the early stages of the growing season.
On leaves, small dark brown to black circular lesions appear after rain in the spring (Figure 1).
Several leaves or shoots can be infected in a localised area, with the more severely infected leaves showing the greater number of leaf spots. Small lesions expand with the leaf and eventually the centre of the lesion falls out, leaving the leaf with a 'shot hole' appearance (Figure 2).
Infected leaves often have a distorted appearance (Figure 3).
On shoots, infection is seen as small circular lesions with white to grey centres and a defined dark brown to black margin (Figure 4).
The centres of the lesions can appear flaky as the lesion ages (Figure 5).
Older lesions develop callused edges and the centre is sunken. This can occasionally be as deep as the middle of the shoot. Lesions may merge, creating several larger lesions on the stem (Figure 6).
Severely infected shoots can have lesions that girdle the shoot which is likely to either break off during the season or produce no bunches at all. Loss of shoots reduces the number of viable canes or spurs in subsequent seasons.
Small brown spots appear on berries that enlarge to be purple black in colour and occasionally have grey to white centres.