Disease

Dutch elm disease

Ophiostoma novo-ulmi

A fungus carried by elm bark beetles and through grafted roots between neighboring elms. It plugs the water-conducting wood, and an infected elm may die the season it is infected or over several years.

Signs

• Leaves on one branch or more wilt, curl, yellow and brown in late spring or summer (flagging).
• Brown streaks in the outer wood under the bark of wilted branches.
• The wilting moves down the branch toward the trunk.

What favors it

Elm bark beetles breeding in dead and dying elm wood, and root grafts between neighboring elms.

Prevention

• Remove dead and dying elms promptly, and burn, bury, debark or chip the wood; the beetles breed in elm wood with the bark on.
• Do not prune elms from April through October, when beetles are drawn to fresh wounds.
• Plant resistant elms such as 'Princeton', 'Valley Forge', 'Accolade' or 'Triumph'.

Crops it shows up on

Shade & ornamental trees.

Often confused with

Sources

• Dutch Elm DiseaseMontana State University Extension
• Elm DiseasesPenn State Extension
• Dutch elm diseaseUniversity of Minnesota Extension
• Hold Off Pruning Oaks and ElmsUniversity of Illinois Extension
• Elm cultivarsThe Morton Arboretum

Why →