By Julie Karmeier, Washington County Master Gardener
At local parks or even along county highways, you might spot large sycamore trees that appear to be dying. Leaves have turned brown and are falling off, twigs are lying on the ground underneath the trees, and only a few green leaves are left on the branches’ ends. What is happening to the sycamores?
American sycamores (Platanus occidentalis) are also called American planetree, buttonwood, or buttonball tree. American sycamores are easily identifiable by their bark and the size of their leaves, in addition to single, buttonball fruits that hang on slender stems of the tree during the winter. The American sycamores have a dark gray-brown bark with oblong, plate-like scales. As the tree grows and ages, the bark turns a lighter shade of gray, and the plates begin to shed, leaving a surface that appears almost a creamy white or pale yellow or green. The peeling bark may be caused by the tree’s rapid growth and the subsequent cracking and exfoliating of its bark. Because of their mottled white bark, sycamores have been referred to by some people as “ghost trees.” They are literally stand-out trees in any woodland setting when compared to the darker browns, grays and blacks of other trees.
Another distinguishing feature of sycamores is their leaves, which are the largest single-bladed leaves native to the American forest. These simple, alternate, and palmately veined leaves are broader than they are long, growing 4 to 9 inches wide. They resemble a maple leaf in shape and typically have shallowly three-lobed leaves.
Because these trees can grow up to 115 feet in height and they tend to be somewhat messy, sycamores are normally not used in a landscape setting. American sycamores prefer moist, rich soils, so they are more likely to be found in bottomlands or along the banks of rivers or streams.
Although there are other insects and diseases that can affect sycamores, the reason the trees frequently look like they are dying in the spring months is due to a fungal disease called anthracnose. Anthracnose affects emerging leaves and stems of sycamores in the early spring months of March through May when the weather is cooler and wetter.
The emerging leaves appear to dry up, turn brown and fall off. Examining the leaves shows that sycamore anthracnose appears as angular (not round), with brown spots along the veins. The fungus eventually spreads to cover more of the leaf surface and cankers can form on twigs and older branches. As twigs die back, new twigs will emerge from the same point. Over time these clusters of dead and live twigs end up resembling what looks like a “witches’ broom.”
Anthracnose is a soil-borne disease caused by fungal spores that overwinter in the soil beneath the tree or in dead twigs or cankers on the infected tree. The spores can spread through water movement, whether it be rainfall, dew, or irrigation. Birds that land on infected trees can also spread anthracnose. With the large sycamore trees, good sanitation practices are the best means of controlling anthracnose. If you have American sycamores on your property, prune out any diseased branches and rake the dead leaves and twigs from the ground under the trees and dispose of them properly, which might include burning them. Don’t add the branches or leaf litter to your compost pile because the fungal spores remain in the dead plant material. If sycamore anthracnose is prevalent in your area, you may wish to plant a sycamore hybrid, the London planetree, which has shown some resistance to anthracnose.
Anthracnose is difficult to control, even with the use of a fungicide, but don’t worry. As the weather warms up, the trees begin to recover, and the sycamores leaf out again in late June or early July. Keep an eye on your sycamores to make sure they are recovering over the summer. If they continue to look unhealthy for a long period of time, consider working with a tree care professional or sending a sample to the University of Illinois Plant clinic to check if the tree is suffering from a different ailment. See https://extension.illinois.edu/plant-clinic
For further information about anthracnose, please contact a Master Gardener or your local University of Illinois Extension Office.