Seedling vigor is a function of environment and genetics with the rating quantifying the ability of emerging corn seedlings to grow vigorously early in the growing season, especially if conditions are cold and wet.
Aggressive seedling vigor is desirable during cool growing seasons, because fast growing plants reach pollination sooner, providing longer grain fill and generating higher grain yields. Some hybrids struggle with early season growth during cool, wet springs. The affected seedlings exhibit purple plants, caused by the failure to translocate sugars to the roots. Sugar reacts with sunlight, forming purple anthocyanin pigments. This purple coloring indicates stress on the seedlings and is a visual indicator for potential herbicide injury.