Definition - What does Black Knot mean?
Black knot is a bacterium that attacks wine vines and appears as a black, knotty, bumpy growth on the stems of the vine. Black knot can attack any part of the vine from the roots to the stems and canes, and it can create abnormal growth in the vines at the infection site. Black knot infects vines at a weakened part of the vine that has been injured.
WineFrog explains Black Knot
Caused primarily by the bacterium Agrobacterium Tumefaciens, black knot or crown gall is composed of soft tissue that can grow to several inches in length and diameter on wine vines. The bumpy knot mostly occurs on the stems and canes, however, the bacterium Agrobacterium Tumefaciens can cause lesions on roots and interfere with growth and uptake of nutrients to the vine.
Black Knot typically takes hold on vines due to over or improper pruning, or at graft sites and leads to abnormal and irregular growth and expansion of the vine. Older vines can survive black knot, however, it can kill young vines, especially if it infects the graft site. First identified in 1897 in Italy, black knot is found in most wine growing regions around the world, including China, South Africa, Europe, and North and South America. The bacterium Agrobacterium Tumefaciens can live in the sap of infected vines and can be transferred through propagation material. Vineyards can prevent infection of black knot on vines by ensuring they use healthy roots and grafting stock, as well as by implementing proper vineyard sanitation practices and keeping the vines healthy and injury free.