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Incidence of grape diseases in Maryland vineyards

Ramesh Pokharel: Maryland Dept of Agric

<div>In Maryland, grape growers have been observing symptoms similar to those caused by diseases, nutritional imbalances, and abiotic factors, leading to reduced yield, vine decline and/or death. From 2015-2017, 33 vineyards were surveyed for two exotic pathogens, grapevine yellows (<em>Candidatus p</em><em>hytoplasma austrialense</em> and brown root rot (<em>Phellinus noxius</em>), based on symptoms. Surveys also recorded incidence of downy mildew and crown gall based on symptoms, and collected information on red blotch virus. In addition, the incidence of <a href=""><em>Xylella</em>; <em>fastidiosa</em></a> and virus diseases, such as grapevine leafroll-associated virus (GLRaVs)1+3, and 2, grapevine fanleaf virus (GFLV), <em>Arabis</em> mosaic virus (ArMv), and tomato ringspot virus (ToRSV), was also studied by collecting 1247 leaf samples and testing them in the laboratory, using ELISA kits. No incidence of exotic pathogens was observed. Downy mildew was commonly noted each year in most vineyards and cultivars. Crown gall symptoms were recorded in several vineyards in 2015 and 2016, and one sample in 2017. Out of several red blotch symptomatic vineyards, eight growers reported verified positives for the virus. No samples were positive for GFLV. Low but similar incidences of GLRaVs 1+3 were observed in 2015-2017 in widespread areas and cultivars, whereas incidence of GLRaV 2 was found only in two cultivars. <a href=""><em>Xylella fastidiosa</em></a><span><em>,</em></span> not tested in 2015, was commonly found across the region in many cultivars in 2016, with only 5 positive samples found in one cultivar in 2017. In 2017, ToRV was observed in two vineyards in four cultivars.</div>