Growing degree days are least useful for determining when to do what?

Growing degree days (GDD) are a measure of heat accumulation used to assess plant development stages and predict crop growth. They play a significant role in planning critical agricultural activities, particularly planting, fertilizing, and harvesting, as these activities are closely linked to the temperature and growth stages of the crops.

When deciding on irrigation, factors such as soil moisture levels, precipitation, and crop needs can be more influential than temperature alone. Unlike planting, fertilizing, and harvesting, which are strongly correlated with seasonal temperature variations and the specific development stages of a crop, irrigation decisions often depend on real-time environmental conditions, including soil moisture and crop water demand rather than accumulated heat during the growing season. Thus, GDDs are less relevant for determining the optimal timing of irrigation, making it the least useful choice among the options provided.