Dutch elm disease was described on elm in the Netherlands in 1921. The fungus has been spread around the world by Scolytus bark beetles in elm wood colonized by the beetles. The disease kills branches and entire trees within a few weeks to years. The first sign of Dutch elm disease appears as a sudden wilting of leaves in some branches, but sometimes the entire tree. Willed leaves curl and turn yellow, then brown and fall off the tree.
Most branches then die.
Often this process takes more than a year. Trees that are infected in the spring or early summer often die quickly, whereas those infected in late summer are less affected and can even recover until infected again in subsequent years. When the bark is peeled back there are brown streaks in the outer wood. O. novo-ulmi has been supplanting the predominant O. ulmi subspecies. When the beetles mature they leave the brood tree and fly away to spread the fungus to new trees.