The incubation period occurs from the time of infection until visual foliage symptoms appear on the vine and this can be anywhere from one to eight years. Foliar symptoms can also vary from season to season as well.
Characteristic symptoms include stunted or distorted shoots that are often yellow and cupped with necrotic margins (Figures 1, 2 and 3). The disease may initially only affect one shoot on a grapevine, eventually spreading to multiple shoots. As the disease moves further down the trunk the entire arm can be killed followed by the trunk and eventually the vine.
Bunches on infected shoots are smaller than uninfected shoots and fail to ripen.
Internally the fungus itself is slow growing. It invades through open wounds of the vine and as it progresses towards the roots it kills the internal tissue. This is characterised by internal wedge-shaped lesions of dead tissue when shoots or arms are viewed in transect at pruning time (Figure 4).
Externally the disease produces fruiting bodies on the wood of the vine (arms, trunk) that are revealed when the bark of the vine is removed. The mass of fruiting bodies appears as a charcoal coloured area on the vine (Figure 5).
It can take up to eight years after the initial infection before the development of the fruiting bodies.