In many parts of North America, people will soon enjoy one of nature’s finest shows—fall foliage. Color-changing leaves make for a beautiful display, but early changes in leaf color can be a sign that a tree is stressed and vulnerable to insect and disease attack.

“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 when the weather turns cold,” says Tchukki Andersen, BCMA, CTSP and staff arborist with the Tree Care Industry Association. “Occasionally, only one or two limbs of the tree will show premature fall color. This could be a sign of a disease at work, though only the infected limbs are weakened.”

The more common situation is for the entire tree to exhibit premature fall coloration, a phenomenon usually linked to root-related stress. “Trees respond to these stresses by trying to curtail their above-ground growth,” adds Andersen.

Leaves can be thought of as small factories containing raw materials, products and byproducts, all in chemical form and some with color. As the leaf is “abandoned” by the tree, the green chlorophyll—the dominant chemical found in most leaves—is broken down and “recycled,” leaving behind other-colored chemicals. Supply lines to the leaves also become clogged, affecting which chemicals are left in the leaf. If the major 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 fluctuating weather conditions, which can affect the balance of chemicals and their composition in the leaves,” Andersen says.

Differing amounts of rainfall, sunlight, temperature, humidity and other factors may have an effect on how bright and how long the “leaf-peeping” season will be in any given year.

For more information, visit www.treecaretips.org.

This article was submitted by the Tree Care Industry Association (TCIA).