Grapevine is a plant of warm climate: it requires a sufficient amount of heat for growth. As its development is strongly influenced by daily temperature, grape growers often use weather-based indicators to predict vine growth stages such as bloom, veraison, and maturity. The growing degree day calculator is one of the most known tools to predict plant development rates.

Growing degree days (GDDs) also help grape growers to predict the development of different grapevine pests. Insects, just like vines, need a sufficient amount of accumulated heat in the season to emerge. With the help of calculated GDDs, vineyard managers can predict when the insects will be active or when they will be in the most vulnerable phase. Hence, the grower can effectively suppress them with a minimum impact on the environment.

Apart from those two reasons, growing degree days are useful also for:

• prediction of the suitability of a region for the production of a particular grapevine variety;
• prediction of the best timing of fertilizer or pesticide application;
• estimation of the heat stress;
• comparing one region to another and one season to another.