P&PDL Picture of the Week for
September 4, 2006

Late Summer Leaf Fall in Trees

Mike Mickelbart, Dept. of Horticulture & Landscape Architecture and Janna Beckerman, Dept. of Botany & Plant Pathology, Purdue University

The tuliptree (Liriodendron tulipifera) shown in the photo is exhibiting yellow leaves in late summer – far earlier than the typical fall defoliation. This phenomenon occurs in a number of species, but tuliptree and river birch are two plants in which late summer leaf drop is common.

The leaf drop is most likely a response to low soil moisture levels near the end of the growing season. When soil moisture levels are low, there is not enough water to support all of the leaves on the tree. Rather than create a situation where all the leaves are supplied with a limited amount of water, trees and shrubs will often “self-prune” or “self-thin” their canopies so the remaining leaves are supplied with adequate water. This keeps the tree in overall better health than it would be if it tried to retain all of its leaves.

Early yellowing or other coloration could be a result of environmental stress or pest or disease, so it is important to check your plants thoroughly. However, trees that look like this tuliptree are not necessarily in trouble.

Click image to enlarge

Photo courtesy of

Janna Beckerman

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service