Dutch elm disease affecting Kalispell trees

The Daily Inter Lake

Dutch elm disease has been identified as the cause of die-off in several American elm trees in Kalispell.

The disease also is suspected in the decline of many trees in Flathead County, according to a news release from Kalispell Parks and Recreation.

Tree samples sent to the Plant Diagnostic Lab at Montana State University tested positive for Dutch elm disease.

Dutch elm disease is caused by a fungus that is spread from tree to tree by beetles and to neighboring elm trees by root grafts. The lesser European elm bark beetle was identified as the insect responsible for the outbreak in Kalispell.

There are a number of signs that homeowners can look for if they think they might have a tree with Dutch elm disease.

First, the tree will display wilting of leaves on individual branches in the crown of the tree that ultimately progresses through the whole tree. In advanced infestations, galleries where the beetles lay eggs are often seen directly under the bark of the trunk. Galleries appear as a complex pattern of shallow tunnels originating perpendicular to a vertical chamber.

The twigs will often show signs of the fungal infection, and this will appear as a dark stain in the tissue underneath the bark.

The most important factor in limiting the spread of Dutch elm disease is sanitation.

Diseased elm trees should be removed as quickly as possible and destroyed. If the wood is to be kept for firewood, the bark must be removed. If the bark is left intact, the beetles can overwinter in branches larger than 4 inches and travel to healthy trees.

It is critical to destroy infested trees by May, when the beetles emerge and may potentially move to other trees. The beetles typically travel only 1,000 to 1,500 feet. Although they are weak flyers they can travel long distances on air currents.

Tree-to-tree spread by root grafts can be limited by trenching the soil between infested trees and healthy trees. The trenches can be dug with a mechanical trencher, and should be 24 to 30 inches deep.

High-value trees sometimes can be saved by injecting fungicides into the tree, but this is only effective at the very earliest signs of disease.

Early diagnosis is the key to limiting the spread of this devastating disease of elms. Samples for diagnosis can be taken to the MSU Flathead County Extension office in the east annex building at the old courthouse complex.

Kalispell Parks and Recreation is currently working on removing infected American elm trees. The wood from these trees is being ground and chipped for use in Glacier High School's biomass furnace.

If you have questions regarding Dutch elm disease, call 758-7715 or 758-7960.