Thursday, August 28, 2008

Landscape - Late Summer Premature Leaf Fall

Late summer premature leaf fall is a common occurance in some trees and shrubs. The following is more information.

Tuliptrees (Liriodendron tulipifera) are exhibiting yellow leaves at this time – 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.

Leaf drop in tulip tree. Photo courtesy of Janna Beckerman, Purdue University.

The leaf drop is 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 partially defoliate are not necessarily in trouble.

Adapted from "Late Summer Leaf Fall in Trees" by Mike Mickelbart, Dept. of Horticulture & Landscape Architecture and Janna Beckerman, Dept. of Botany & Plant Pathology, Purdue University, Purdue Plant and Pest Diagnostic Laboratory.

No comments: