M.F. Heimann, P.J. Pellitteri
Despite their name, evergreen needles do not stay green forever. Older, inner needles discolor and drop off after one or more years, depending on the species. Sometimes the drop occurs slowly; other times, large numbers of needles yellow simultaneously in late summer or early fall, making for a striking spectacle.
Because the condition is triggered by the weather and the season, many evergreens are likely to show symptoms at the same time. This phenomenon, which especially affects white pines, could easily be mistaken for disease or insect damage. This fact sheet will help you understand the signs of seasonal needle drop and how they differ from signs of disease or disorder (2 pages).