Gypsy moths, Emerald Ash Borer and now the Maples? UW-Extension explains, no need to worry about the black spots on your Maple leaves:
This spring the Dane County UWEX Horticulture staff have been inundated with calls and emails from homeowners reporting that leaves on their silver maples are blackening and falling off.
The symptoms are caused by two groups of fungi, according to Brian Hudelson, Plant Disease Diagnostics Clinic director on campus. One is called anthracnose, the other, Venturia leaf blotch. For most trees, both are usually just a cosmetic problem rather than a significant health issue.
“We get these calls very commonly when we have cool, wet spring weather,” says Lisa Johnson, the Dane County UWEX Horticulture Educator. “Anthracnose also can infect ash and oak, so some years, we get calls about the disease on these trees as well. People are happy to hear that it is generally not a major problem. Typically, we don’t recommend a chemical treatment for anthracnose or Venturia leaf blotch; only to rake up any fallen infected leaves so that they can’t provide more inoculum for future infections.” Both diseases should disappear as the weather becomes warmer and drier over the season.
The diseases can be problematic for young trees that have recently been planted and have fewer leaves to begin with, or for larger trees that have been completely defoliated by the disease several years in a row. In those cases, chemical control may be warranted. However, at this time, since most fungicide products protect against new infections rather than cure those already present, it is too late to spray. To learn more about available chemical treatments and when to apply them, visit the online factsheet for anthracnose here.
