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Investigating the cause of red blotch disease in Grapevines (Vitis spp) in Oklahoma.

Sara Wallace: Oklahoma State University

<div>The value of the Oklahoma grape industry was $98 million in 2010. Grapevines (<em>Vitis spp</em>) in Oklahoma were surveyed to elucidate the cause of red blotches on leaves. A 2-year Cooperative Agricultural Pest Survey was initiated and 121 grapevines were sampled in 13 counties in 2016 and in 2017 samples were collected from 96 grapevines from 14 counties. Each sample was tested for <em>Grapevine red blotch associated virus</em> (GRBaV), Pierce’s Disease (<em>Xylella fastidiosa</em>), and Phytoplasma spp by Polymerase Chain Reaction (PCR). ELISA was used to test for GLRaV strains 1+3 and 4-9. A chemical test and microscopic morphological identification were conducted for Rotbrenner (<em>Psudopezicula tracephila</em>). GRBaV was detected in 38%, GLRaV 1+3 16%, GLRaV 4-9 2%, and Pierce’s 2%, there were no detections of Phytoplasmas in 2016 and 2017.Rotbrenner was not tested in 2016. GRBaV was detected in 34%, GLRaV 1+3 17%, GLRaV 4-9 3%, and Pierce’s 3% in 2017. No Phytoplasmas nor Rotbrenner were detected in any of the samples in 2017. Mixed infections were found in 20/121 in 2016 and 19/96 in 2017. The data generated by this survey is informative to the grape industry, growers, and extension personnel about which diseases are affecting grapevines in Oklahoma to communicate effective management strategies since each of the surveyed diseases has a different vector.</div>