Remote sensing technology is increasingly used in agriculture to monitor plant health by detecting signs of stressors such as drought, nutrient deficiencies, or diseases. These technologies rely on measuring how plants reflect light, which changes when they are under stress. However, many current approaches focus mainly on detecting changes to make maps, without fully understanding the underlying biology of the plant and its response to the stressor, which changes with growth stage. Using potatoes and early blight disease as examples, we show how different plant functions and responses create unique patterns in the light they reflect. By understanding these patterns, farmers and researchers can better identify problems and take targeted actions. We aim to emphasize the importance of combining plant science with remote sensing to improve how we detect and manage crop stress, ultimately helping to make agriculture more precise, efficient, and sustainable.