American sycamores (Platanus occidentalis) are extremely susceptible to this disease. On the other hand, London planetrees (Platanus X acerifolia), which are like sycamores, are much more resistant, though they do get the disease.
The pathogen enters the buds, emerging foliage, and eventually twigs during wet, cold periods in the spring. Bud death, new leaf death, and larger leaves with the symptoms drop off. The result is a landscape full of leaves on the ground.
When buds are killed, adventitious buds (those that are on the plant in unexpected places that emerge when other parts of the plant are killed) emerge. After several years of this occurrence, witch’s brooms develop on the stems.
Witch’s brooms occur when there is a proliferation of shoots growing close together. They can be caused by fungus, virus, phytoplasmas, environmental damage, and other reasons. The result is a lot of branch growth in a small area.
Look at a sycamore that is almost defoliated by anthracnose, and you may see these witches’ brooms on the branches. Look for a dense cluster of branches at the end of twigs.
Some witches’ brooms are propagated and developed into landscape plants. For instance, Dwarf Alberta spruce is a naturally formed, juvenile version of the white spruce. It has been in the landscape for years.
Perhaps you have seen one that has reverted to the white spruce? It’s not uncommon for this plant to have a branch or two that revert to its parent. You will see a large growth of white spruce coming out of the pyramidal parent Alberta spruce.
Back to the sycamores – this disease won’t kill a sycamore. It may weaken it if it happens time after time, but I have seen sycamores have it for many years in a row and not be negatively affected.
The leaf litter is annoying. Branches may drop due to the pathogen affecting the stems and new branches. Leaves on the ground will either be completely brown or have tan-brown blotches along the veins.
I have been around the Miami Valley quite a bit lately and have noticed varying levels of symptoms on sycamores. Some are almost totally defoliated, while others were not as affected.
There is little to do to prevent this problem. It is quite costly to apply fungicides on large trees, and fungicides must be timed accurately to prevent the disease.
My recommendation is to rake up and dispose of the affected leaves and stems, and not worry about it.
Many other landscape plants are also affected by different species of anthracnose. I have had reports of maple trees with anthracnose as well. This is not as widespread as the sycamore anthracnose.
Pamela Corle-Bennett is the state master gardener volunteer coordinator and horticulture educator for Ohio State University Extension. Contact her by email at bennett.27@osu.edu.
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