Ophiostoma ulmi is a fungal pathogen known for causing Dutch elm disease, a serious disease affecting elm trees. It primarily spreads through bark beetles, particularly the Scolytus species, which carry the spores from infected trees to healthy ones. The fungus blocks the tree's vascular system, leading to wilting and eventual death. This pathogen was first identified in the early 20th century and has significantly impacted elm populations in North America and Europe. Efforts to manage the disease include removing infected trees and breeding resistant elm varieties to help preserve these important urban and forest trees.