The Esca complex in German vineyards: does the training system influence occurrence of GLSD symptoms?
The Esca complex is one of the most destructive grapevine trunk diseases (GTDs) worldwide. Several factors, such as plant age, grapevine cultivar, or pattern of precipitation have been identified as possible driving forces of the disease. In the present study, a 4-year monitoring of grapevine leaf stripe disease (GLSD) symptoms in vineyards located in three areas in Rhineland-Palatinate was conducted. Vineyards of different age and planted with different cultivars, both traditional and new ones tolerant against Powdery and Downy Mildew, were chosen. All vineyards were equally subdivided into minimally and intensively pruned sections. The following aspects with regard to the training system were investigated: i) the occurrence of GLSD over the season; ii) the possible influence of cultivar, plant age and precipitation on symptom development; and iii) the possible impact of the training system on the incidence of GLSD. The seasonal patterns of symptom appearance in general were identical for the years 2015, 2016 and 2017. In 2018, however, the maximum peak of newly affected vines was reached about 4 weeks earlier, which is probably linked to the fast phenological development of the vines in this particular year. The training system did not affect the seasonal symptom appearance. All investigated parameters, i.e. cultivar, plant age and precipitation, were shown to have at least some influence on symptoms incidence, even though some of the results were inconsistent over the period of monitoring. Concerning the influence of the training system, in 2015 no differences between minimally pruned (1.8%) and intensively pruned (1.9%) vines were found. However, in the following year minimally pruned vines (6.9%) expressed significantly more symptoms than intensively pruned vines (4.9%). In the years 2017 and 2018 the opposite was the case. 2.6% and 2.4%, respectively, of the minimally pruned vines showed GLSD symptoms, while for the intensively pruned vines the mean values were 4.5% and 3.6%, respectively. Our study represents the first systematic GLSD related data collection in German vineyards over an extended period of time.