A devastating disease which can affect all species of elm (Ulmus). The causal agent is Ceratocystis ulmi, a fungus which appears to have originated in Asia, not Holland. The fungus develops and spreads in the xylem vessels; tyloses are formed. Symptoms include wilting, with curling and yellowing of foliage, followed by rapid death of branches or the whole tree. The fungus is spread from tree to tree by elm-bark beetles (commonly Scolytus species). In the 1960s a new and more virulent strain of the pathogen was introduced into Britain on logs imported from Canada; many millions of elms were killed, dramatically changing the landscape in many regions of Britain.
Subjects: Ecology and Conservation — Plant Sciences and Forestry.