This article was originally published in the BFEC newsletter, Vol. 20/No. 4, Fall 2016.
By Shane McGuire, BFEC Land Manager & Naturalist
Almost everyone who is native to Ohio has an appreciation for the buckeye. Some might enjoy cheering the scarlet and grey to victory on a Saturday afternoon, while others no doubt enjoy observing our state tree, the Ohio buckeye, in our forests and yards. Personally, I love to watch the buckeye trees flower in the early part of spring and to watch the leaves finally emerge from their buds at the end of a cold winter. I love the excitement of making buckeye necklaces in early fall. But every year as I watch the buckeyes drop their leaves, I find myself wondering why... Why do Ohio buckeyes drop their leaves before most other trees?
It seems that summer isn’t yet finished when I notice the leaves are already changing color, and some buckeyes have already begun to lose their leaves. The first year I noticed this, I wondered if the buckeye trees were dying. But I soon discovered that our tough buckeyes were not dying, but they were battling a few environmental elements.
The first element that affects leaf drop is shading. You might notice that the inner leaves of the tree — those closest to the trunk — are the first leaves to fall. This could be due to the outside leaves shading the inner leaves causing them to change color and drop. This same concept can be applied to the entire buckeye tree if it is surrounded by taller trees. The taller trees will shade the leaves of the Ohio buckeye causing our state tree to drop its leaves early.
The second element is the result of sun exposure and drought conditions during the summer. Ohio buckeyes, like every other tree species, use energy to get water to each leaf. When planted in a full sun location, buckeye trees can experience leaf scorch during hot, dry summers. Leaf scorch is caused when the tree shuts-off the water supply to some of its leaves making those leaves turn brown and drop from the tree. This adaptation helps the tree conserve energy and water.
The final element, and the factor that probably plays the largest role in early leaf drop, is a fungal disease called leaf blotch. The fungus, Guignardia aesuli, attacks the leaves of our Ohio buckeye as well as other tree species in the Horse Chestnut family. If you look closely at buckeye leaves in mid-summer you might notice reddish-brown spots surrounded by yellow tissue. By late summer the leaves become brown and twisted as the disease spreads. In severe cases, the leaves will fall prematurely in late summer. Fortunately, leaf blotch does not seem to seriously hurt the tree. Since the foliage is usually not badly damaged until after the tree has completed much of its annual growth, the disease is primarily aesthetic.
If you have a beautiful buckeye planted in your yard and you suspect that it is battling leaf blotch, there are several things you can do to help. After all the leaves have dropped, simply rake them up and dispose of them. If the leaves are left on the ground over the winter, your tree may be infected again the next year. The Guignardia fungus overwinters on fallen leaves. In early spring, the spores will be released into the air. If these spores land on newly developing leaves that remain wet for several hours, the leaves will become infected. You could also lightly prune the tree in the fall to thin the tree canopy. This will improve air circulation and allow the leaves to dry more quickly after a rain.
The practices mentioned above will prevent the spread of leaf blotch; however, the only measure that will cure it is to apply a fungicide. Several applications must be applied after the leaves emerge.