We recently had a Norton (aka Cynthiana) vine submitted to our clinic by Clark McAllister (county agent in Lumpkin County), and the vine(s) were showing odd symptoms for Norton. Leaves were somewhat chlorotic, but the major concerning symptom was a ring spot on the leaves, along with spots on the shoots which are similar to those of Phomopsis (see attached).  The plant was eventually diagnosed with grapevine red blotch associated virus (GRBaV).  We have previously identified this virus on vinifera grapes, but this might be the first report of this virus on Norton (aestivalis).  Without regard, it is a first report for Georgia.  If you see Norton with similar symptoms, this could be the cause.  The symptoms observed on Norton are generally different from previously observed symptoms in vinifera, and I am not sure how consistent these will be. See attached for a fact sheet on GRBaV for vinifera, as symptoms are very similar in many cases to those of leaf roll virus.   If the results of viral infection are consistent, we can expect infected Norton plants to show reduced photosynthesis, less pruning weight (growth), lower sugars, uneven ripening, and possible decline over time.  However, all of this is speculative at this point, and impact may be minimal.  If you do observe odd symptoms on Norton, please report this to your county agent.  Nutrient issues or mites (yellowing) could also be at play, but the ring spot is unique.

Norton Grapevine Red Blotch Associated Virus Symptoms

Grapevine red blotch associated virus