Disease susceptibility of cold-climate grapes in Vermont, USA

Fungal diseases and cold temperatures can be limiting factors when growing winegrapes in the northeastern USA. A research vineyard was planted at the University of Vermont Horticultural Research and Education Center in South Burlington, Vermont in 2007 with winegrape cultivars considered to be the most “promising” based on the experience and insights of Vermont grape growers. A randomized complete block design of six replicated blocks with four-vine plots of each cultivar per block was used and included six cultivars: 'Frontenac', 'La Crescent', 'St. Croix', 'Marquette', 'Prairie Star' and 'Corot Noir'. The vines were planted at a spacing of 1.8×3.0 m and trained to a high-wire cordon system. All cultivars received the same fungicide treatments each year totaling five in 2014 and six in 2015. Foliar and fruit cluster disease assessments including incidence and severity measures were performed each year. Diseases assessed included powdery mildew (Erysiphe necator); downy mildew (Plasmopara viticola); black rot (Guignardia bidwellii); Phomopsis leaf spot and fruit rot (Phompsis viticola); angular leaf scorch (Pseudopezicula tetraspora); anthracnose (Elsinoe ampelina); and Botrytis bunch rot and blight (Botrytis cinerea). There was no single cultivar that was consistently more resistant to all the foliar or cluster diseases in this study and the ranking of cultivar susceptibility varied depending on the growing season and the disease. It is important to note that powdery mildew emerged as the most prevalent cluster disease with all cultivars showing at least 93% incidence in both growing seasons. Cultivars differed in foliar susceptibility to downy mildew, yet no symptoms on the fruit were observed in either year. Although disease susceptibility is an important component of selecting a cultivar, future research should incorporate yield and marketability, non-sprayed plots, comparison of multiple fungicide programs and the impact of training systems.