What is Dutch Elm Disease (DED)?
DED is caused by a fungus called Ophiostoma ulmi, formerly Ceratocystis ulmi, that was introduced to the U.S. in the early 1930s. The native elm bark beetle and the European elm bark beetle are responsible for transmitting DED. The disease can also be transmitted through root grafts that are prevalent in cramped urban and suburban parkways. The disease is most easily detected during early summer when the leaves on an upper branch curl and turn gray-green or yellow and finally brown. This condition is known as flagging. Brown streaks in the wood beneath the bark of affected branches is further evidence. If a tree is less than five percent infected, it may be saved by pruning out the diseased branch promptly after seeing the first flag. If a tree shows many flags or completely wilts and dies, it must be removed quickly so that the beetles and root grafts do not transmit the disease further.
