In many parts of North America, people will soon enjoy one of nature’s finest shows. The changing colors of fall foliage make for a beautiful  display, but too-early changes in leaf-color can be a sign that your tree is  stressed and is susceptible to attack by insects and disease.  

 Leaves can be thought of as small factories containing raw materials, products  and by-products—natural chemicals, each with a different composition and color. As the growth  season ends, supply lines to the leaves become clogged, and the leaf is “abandoned” by the tree as it moves into its cold-weather phase. The green chlorophyll—the dominant chemical found in most leaves—is broken down and “recycled,” leaving behind other-colored chemicals. If the primary chemical remaining in  the abandoned leaf is red, the leaf turns red. If it’s yellow, the leaf turns yellow, and so on.  

 The yearly variation in color intensity is due to varying weather conditions,  which can affect the balance of chemicals and their composition in the leaves. Differing levels of rainfall, sunlight, temperature, humidity and other factors  may have an effect on how bright, how quick, and how long the “leaf peeping” season will be in any given year.  

 Premature color change can be an indication that a tree isn’t vigorous enough to withstand insects and disease organisms that may attack it—not to mention the usual changes that occur naturally when the weather turns  cold. Occasionally, only one or two limbs of the tree will show premature fall  color, which can be a sign of a disease at work, weakening only the infected  limbs. The more common situation however, is for the entire tree to exhibit  premature fall coloration, an occurrence usually linked to root-related stress.  Trees respond to these stresses by trying to restrict their aboveground  growth.       

 If the leaves on your trees seem to have gotten a jump-start on fall compared  with those on similar trees in the area, you might want to consult a  professional arborist who can identify any problems and offer possible  solutions.

 Sam deTuro is chairman of Woodwinds Associates, Inc., a tree care and  landscaping firm based in Princeton.