Definition - What does Black Measles mean?
In regards to wine, the black measles, or grapevine measles also called esca, refers to black spots found on the surface of grapes. It can develop anytime from the fruit set to days up to harvest.
Infected fruit will dry and shrivel and give the grapes an off-taste of something very bitter and pungent.
WineFrog explains Black Measles
The symptoms of black measles can be identified on the leaves, as they take on a tiger-stripe pattern, although, some symptoms do not show each year. More extreme cases occur in seasons with heavy rains and high temperatures in the growing season. If the symptoms are acute, a vineyard can die within one year, as it affects more than just the fruit and leaves - it affects the entire vine. This is identifiable when the vine is cut and black sap emerges.
As of present, there is no cure for black measles, but research is getting closer to a solution.