First detected in Mandan, North Dakota in 1969, Dutch Elm Disease (DED) is a fungus that is spread by elm bark beetles. When an elm tree is infected with DED, branches in the upper crown will yellow, curl and wilt, commonly referred to as flagging. If a healthy elm tree is next to a tree infected with DED it is possible for the fungus to spread through the root systems. This happens when trees are planted close together and as they mature their roots fuse together, also known as root grafting.
Several options are available to help minimize the spread of DED:
Beetles overwinter under the bark, so it is very important to dispose of elm wood by burning, burying, chipping or debarking.
Severing Root Grafts
A viable option only if the infected tree is less than 25%. Trenches at a depth of 40" (inches) should completely encircle the infected tree. Fill in the trenches with soil and remove the infected tree. If the tree is infected more than 25%, it is likely that the fungus has spread to the surrounding elm trees.
There are treatment options available; however, it can become costly and may do more harm than good in the long run.
Plant Resistant Varieties
Many DED-resistant cultivars are available in the nursery trade.
Accolade, Cathedral, Discovery, Jefferson, New Horizon, Patriot, Prairie Expedition, Princeton, Triumph and Vanguard are a few examples that have proven successful.