Disease evaluation of selected cold climate wine grape cultivars in Vermont, USA
Abstract: Cold climate wine grape production is a “new” crop in the diversification of agriculture in Vermont and other northern states. In the past, commercial wine grape production was not recommended in the colder regions of the USA because of problems with winter survival of the vines. However, cold climate wine grape cultivars are now available which survive -34 °C to -37 °C winter temperatures. In addition to cold hardiness, these interspecific hybrids were bred for disease resistance and potentially may require less overall fungicide use to produce highquality fruit. Few research studies have been conducted to determine their relative disease susceptibility and fungicide requirements. The purpose of this study was to compare disease incidence and severity during the 2010-2012 growing seasons among a selection of wine grape cultivars planted at the University of Vermont vineyard which included: Frontenac, La Crescent, St. Croix, Marquette, Prairie Star, Corot Noir, Vignoles, and Traminette. During each growing season, all cultivars received the same fungicide treatments totaling four to five applications each year. The following fungicides were applied either alone or in combination: mancozeb, mycobutanil, kresoxim-methyl, and captan. At the end of each growing season, disease incidence and severity were determined by examining 20 randomly selected leaves per plot and by visually assessing ten randomly selected fruit clusters per plot. Diseases that were assessed included: powdery mildew (Erysiphe necator); downy mildew (Plasmopara viticola); black rot (Guignardia bidwellii); Phomopsis leaf spot and fruit rot (Phomopsis viticola); angular leaf scorch (Pseudopezicula tetraspora); and anthracnose (Elsinoe ampelina). Powdery mildew was the most prevalent disease and was observed on the foliage of all cultivars in each year. Frontenac or Prairie Star ranked the highest numerically in percent leaves infected but were not significantly different from some of the other cultivars. No powdery mildew was observed on any fruit in any year. Downy mildew was also observed only on foliage and not on any fruit over the three years of the study. In 2010 and 2011, the highest foliar incidence was observed on Vignoles; in 2012, the highest foliar incidence was observed on La Crescent vines although Vignoles vines (and Traminette vines) were removed from the study at the beginning of the 2012 growing season and were no longer part of the study. Phomopsis foliar symptoms were not observed in any year but fruit rot symptoms were observed in 2010 and 2012. In 2012, Frontenac had the highest incidence and severity, followed by Marquette. Black rot, angular leaf scorch and anthracnose were either not observed or at very low incidence during the three growing seasons. In summary, differences in disease incidence and severity among the cultivars were observed for some diseases. Future research which allows for comparison of multiple fungicide programs during a growing season is needed to determine the innate disease resistance/susceptibility of these cultivars and how best to incorporate this knowledge into effective disease management programs that address economic, health, and environmental concerns.