Anthracnose on sycamore

Every wet spring, sycamore trees in the eastern US appear to be dying. Leaves brown and fall. Entire branch tips die back. Alarmed homeowners call arborists and Extension offices in large numbers. In almost every case, the diagnosis is the same: sycamore anthracnose, a cool-weather fungal disease.

Every wet spring, sycamore trees in the eastern US appear to be dying. Leaves brown and fall. Entire branch tips die back. Alarmed homeowners call arborists and Extension offices in large numbers. In almost every case, the diagnosis is the same: sycamore anthracnose, a cool-weather fungal disease that is severe in appearance but rarely fatal to the tree.

Sycamores are among the most anthracnose-susceptible trees in the eastern US. The disease is so common and predictable that a sycamore without anthracnose symptoms in a wet spring is the exception. The practical good news: most established sycamores releaf by mid-June and continue growing with no lasting structural damage.

I don't grow sycamores at my Long Island property, so this guide is sourced from University Extension and USDA Forest Service research.

The pathogen

Sycamore anthracnose is caused by Apiognomonia veneta (formerly classified as Gnomonia leptostyla var. platani). Per University of Minnesota Extension, this fungus overwinters in infected twig tissue and on fallen leaves. Spores are released during cool, wet weather in spring, infecting expanding leaves, shoots, and small twigs. Infection slows dramatically as temperatures rise above 60°F (16°C) in late spring.

The same fungal genus infects other tree species, but each form is host-specific. Apiognomonia veneta infects only Platanus species (sycamore, London planetree).