red blotch virus or red blotch disease, a new circular DNA geminivirus first described by scientists at cornell and UC davis in 2012, is now being recognized as a serious problem in the US. At least two strains have so far been identified and more are likely. Much remains to be learned but this virus is known to seriously impair the ripening potential of the fruit in infected vines. Symptoms include red blotchy leaves in red wine varieties and yellow curled leaves in whites, although infected symptomless vines have also been seen. The origin of this ‘new’ disease is unknown but the primary source to growers now is infected plant material that was previously certified free of known viral pathogens. In addition, it is strongly suspected to be spread from sick to healthy vines via insect vectors, possibly leafhoppers. Virtually all nurseries in California, including the foundation plant service at UC Davis, are testing for and eliminating red blotch from their mother vines. They are planting new source blocks in virgin ground with the latest certified material that has also been tested for the new virus in the hope of eliminating it from the plant material stream. By the end of 2014, the presence of this virus had been recorded in nursery plants in California and it has spread in the US and perhaps in Canada.
