Dutch elm disease found in local trees

Early intervention can prevent spread of disease

The Daily Inter Lake

Dutch elm disease has been identified as the cause of the die-off of several American elms in Kalispell. The disease also is suspected in the decline of elm trees elsewhere in Flathead County.

The trees in question were first noticed by Kalispell Parks and Recreation and samples were sent to the Plant Diagnostic Lab at Montana State University, where they tested positive for Dutch elm disease.

An information booth will be set up this week at the Northwest Montana Fair. For more information or questions contact the MSU Flathead County Extension office at 758-5553.

"We caught it fairly early here," said Wesley Gwaltney, the county extension agent. He said American elms are not widespread in Kalispell and he is optimistic that early intervention can curb the spread of the disease.

Dutch elm disease is caused by a fungus 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 trees with Dutch elm disease.

First, the tree will display wilting leaves on individual branches in the crown of the tree that ultimately progress 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 often will 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 in diameter and then 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 fliers, they can travel long distances on air currents.

Tree-to-tree spread by root grafts can be limited by trenching the soil between infested and healthy trees.

The trenches can be dug with a mechanical trencher, and should be 24 to 30 inches deep. Extremely high-value trees can 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.

Samples for diagnosis can be taken to the MSU Flathead County Extension office in the east annex building at the old courthouse complex in Kalispell.