Dutch Elm Disease
Ophiostoma ulmi, Ophiostoma novo-ulmi
Overview
A lethal vascular wilt disease of elm trees spread by bark beetles and root grafts. It has devastated elm populations across North America and Europe since the early 20th century.
Symptoms
Wilting and yellowing of leaves on individual branches (flagging), progressing throughout the crown. Brown streaking in sapwood visible when bark is peeled. Rapid death of large branches or entire tree within weeks to months.
Environmental Conditions
Variable
Prevention
Plant resistant elm varieties (Valley Forge, Princeton). Disrupt root grafts between trees. Remove dead and dying elms promptly. Control bark beetles. Prune elms only during dormancy.
Management
Fungicide injection (propiconazole) can protect healthy trees or treat early infections. Prune infected branches at least 10 feet below symptoms. Remove and destroy infected trees. Sever root grafts.