Abstract <p>Over the past century, the species richness of alien mycobiota associated with trees and shrubs in the boreal regions of Russia has increased exponentially. This is due to the rapid growth in the number of introduced host plant species, which is due to increased trade volumes and global warming. New data are coming in, thanks to which catastrophic scenarios for the spread of new plant diseases are being corrected. The problem of uncontrolled greening of cities is being discussed, as a result of which botanical gardens, parks, and gardening centers are recognized as foci of concentration and penetration of new diseases deep into the continent.</p>