In the megapolis, native and adventitious species of woody plants are exposed to the most powerful adverse environmental factors that reduce resistance to diseases and pests. The investigation objective was to identify diseases and pests of a dangerous invasive species Acer negundo L. and to estimate their effect on invasion activity of this species. A. negundo leaves are affected by Рhyllosticta negundinis (Sacc. et Speg.), Sawadaia bicornis (Wallr. ex. Fr.) Miyabe and are occasionally damaged by a timber pest such as Rhopalopus clavipes F. A set of unfavorable environmental factors cause noninfectious toxicosis of A. negundo leaves. Meanwhile, all these diseases and pests do not cause considerable harm to A negundo and do not substantially reduce its invasion activity.