Tar Spot (Rhytisma acerinum) in North America from 1985-Present

Norway Maple (Acer platanoides) is an invasive tree that was introduced to the United States in 1856. This maple tree is known to be brought here from England. After the trees introduction to the United States it was and still is a commonly planted tree in urban landscapes with multiple cultivars like Olmstead’, ‘Emerald Queen’, and ‘Crimson King’ . Norway maples are regulated at the state level in eleven states. The tar spot that occurs on Norway maples is called (Rhytisma acerinum) and was first identified by Hudler et al. 1987 in New York. This tar spot is believed have originated in Europe according to Held et al. 2018. Since the tar spots identification in 1987 it has continued to move throughout the east coast states where Norway maples are located and has slowly started to spread west. In 2018 it was noted in Minnesota by Held et al. 2018 and has caused severe defoliation of Norway maples. The map above shows where Norway maples are located throughout the United States (in green). The map also shows where Rhytisma acerinum was first identified (in red) and where it has been officially reported (in orange). It should be noted that Rhytisma acerinum is likely found where ever Norway maples are in the eastern half of the United States and Midwest. The above map only indicates official identification of the disease.