Researchers have discovered a fungus attacking Norway Maples in the United States. It causes tar spot disease and appears to be causing a decline in sapling and tree growth.
‘Tar Spot Disease on Norway Maple in North America: Quantifying the Impacts of a Reunion between an Invasive Tree Species and Its Adventive Natural Enemy in an Urban Forest’ Marie Lapointe and Jacques Brisson. Ecoscience Mar 2011 : Vol. 18, Issue 1, pg(s) 63-69 doi: 10.2980/18-1-3378.