Base Temperatures for Budbreak and Leaf Appearance of Grapevines

Cuttings from 10 cultivars of Vitis vinifera L., one of Vitis labrusca, and one French hybrid were taken, after cessation of winter dormancy, from six vineyards into seven controlled temperature regimes with day/night temperatures of 10/5°C to 30/25°C. Rates of budbreak and leaf appearance were used to estimate base temperatures for each cultivar. Base temperatures for budbreak ranged from 0.4°C to 4.6°C (mean 3.5°C), and for leaf appearance they ranged from 5.0°C to 8.0°C (mean 7.1°C). The two methods used to determine base temperature, extrapolation, and minimal coefficient of variation, gave similar results. Predictions were made of budbreak dates and of leaf numbers using relationships derived from the controlled-temperature results. Predicted dates of budbreak in four vineyards were within six days of observed dates in nine out of the 10 cases tested. Leaf numbers closely followed observed values up to the stage of flowering and fruit set. It is suggested that base temperatures of 4°C for the budbreak phase and 7°C for the leaf appearance phase should be used for grape in place of the currently accepted value of 10°C.