Late Summer Leaf Fall
Mike Mickelbart, Dept. of Horticulture & Landscape
Architecture and Janna Beckerman, Dept. of Botany & Plant Pathology,
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.