Maple : premature fall color

Each August brings a few trees that begin the fall color frenzy ahead of schedule. In addition to signaling the change of seasons, these trees are sending a clear signal that they are suffering from some form of stress. Stress can have a wide variety of causes, be mild or severe, or, benign or fatal. In any case, professional tree "care givers" should be aware that the trees are talking to you. Are you listening?

Maples are probably the group of trees that most commonly exhibit premature fall color. Sensitive to changes in their environment, maples commonly show early color in years when summer rains are heavier than normal and raise soil moisture to or above field capacity during the period from mid to late summer. The maples that show this characteristic the best are the several species of soft maples (sliver and red) that commonly inhabit the shrubby areas around wetlands. These trees commonly begin to show deep, rich purples as early as the first week in August.

Maples in communities also commonly display early color due to stress mechanisms more common to the urban environment. Sugar maple, in particular, shows early color due to the stress induced by infection from Verticillium wilt. This disease may occur in nursery grown stock in commercial trade. It is difficult to detect because it is soil-borne, difficult to culture, and commonly not tested-for in the nursery. In addition, Verticillium wilt is a relatively weak pathogen that does not do well on young, vigorous nursery stock. Trees can be infected for many years without showing external symptoms of the disease. When they do begin to show symptoms, one of the first is premature fall color followed in succeeding years by a progressive, if not slow, crown decline and dieback.

Maples in communities that are planted "just-a- little" too deep often show premature fall color. Again this is more pronounced in years with wet summers. The likely mode-of-action is decreased soil oxygen content. Planting too deep "smothers" roots reducing oxygen in the root zone. So does over watering whether natural or artificial. The bottom line is stress-induced premature fall color. Remember that stress is (1) caused by many factors, (2) cumulative, and (3) potentially fatal if left untreated.