Since you have seen black specks on the vascular system of the vine, it is most likely one of the symptoms of ESCA disease. Foliar and berry symptoms are vine’s reactions to toxin production by the ESCA pathogen, and thus, it may take some time to develop. Please click this link to learn more about ESCA.
If the discoloration is brown, rather than black, the vine might be suffering from Botryosphaeria, which does not show striking foliar or shoot symptoms. Please click this link to learn more about Botryosphaeria.
Also, cankers can be caused by abiotic factors. Please click this link to learn more about abiotic disorders.
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