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Visual identification of grapevine red blotch associated virus (GRBaV) may be a useful complement to lab testing of tissue samples. While not meant to replace the results from lab tests, visual identification may prove to be a useful method for quickly and cheaply assessing whether GRBaV is present in your vineyard and which vines are infected. However, doing so requires some training. One must know the symptoms well and be able to distinguish them from those of other viruses. Fortunately, anyone can acquire the necessary skills with some practice.

A good place to start learning is the image collection assembled by UC Cooperative Extension viticulture farm advisors Rhonda Smith and Monica Cooper. These high-quality images are good specimens of winegrape leaves expressing GRBaV symptoms in three common varieties: Cabernet Sauvignon, Merlot, and Chardonnay. The images are available on the UCCE Sonoma County webpage (click HERE) and are also included below.

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The following information was taken directly from the UCCE website:

All images in the following table are of specific vines in locations which are under evaluation with grant funding provided by the American Vineyard Foundation. Vines in the photos tested positive for grapevine red blotch associated virus (GRBaV) by PCR-assay. They also tested negative for 20 other grapevine viruses and the bacterium that causes Pierce’s disease.

To insure foliar symptoms of grapevine red blotch disease can be associated with a single virus – GRBaV – UC Foundation Plant Services tested all vines using the current “full panel” of PCR assays. As stated above, each vine tested negative for 20 grapevine viruses (including all grapevine leafroll roll associated viruses). Fewer than half the vines tested positive for grapevine rupestris stem-pitting associated virus; a virus that has not been shown to cause significant disease in grapevines.

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Cabernet Sauvignon

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Merlot

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Chardonnay

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