Viticultural performance of red and white wine grape cultivars in southwestern Idaho

A collection of 23 red and six white wine grape (Vitis vinifera) cultivars were evaluated for viticultural performance in Parma, ID. Vine yield, fruit composition, and vegetative growth were measured over four growing seasons, and data were used to compare relative cultivar performance based on yield to pruning ratio and fruit maturity. Relative differences among cultivars in budbreak day of year [96 (6 Apr.) to 122 (2 May)] and days from budbreak to harvest (143 to 179 days) varied from year to year. The earliest and latest maturing cultivars in 3 of 4 years were 'Blauer Portugieser' (143 days), 'Nebbiolo' (177 days), 'Barbera' (179 days), 'Orange Muscat' (144 days), 'Flora' (149 days), 'Muscat of Alexandria' (166 days), and 'Viognier' (168 days). Cultivars differed in yield (2.4 to 7.0 tons/acre), vegetative vigor (4.6 to 20.4 yield/pruning weight), and harvest soluble solids concentration (21.1 to 26.5), but differences in harvest pH (3.0 to 4.1) and titratable acidity (2.48 to 13.03 g.L-1) varied from year to year. Average heat unit accumulation (1646) was 160 units higher than the 78-year site average. Few (less than 150) units accumulated in April and October, most units accumulated in July, and diurnal difference in air temperature was approximate to 15 degrees C. Performance results from this study can assist cultivar site selection by comparing climate data for an intended site with that of Parma. For example, the low acidity and earliness of 'Blauer Portugieser' suggests it is best suited to a site with less heat unit accumulation than Parma, and the high acidity and late maturity of 'Barbera', 'Nebbiolo', and 'Carignan' suggest these cultivars are best suited to a site with more heat unit accumulation than Parma. The inconsistent relationship between onset of budbreak and earliness observed in this study suggests opportunity to match short-season cultivars late to break bud such as Flora to short-season growing sites prone to late-season frost.