Elm leaf beetles chewing way through Wellington trees

The elm leaf beetle is back in Wellington and is busily feeding on elm leaves, causing them to dry up and die. The result is a whole lot of ugly, brown trees around town.

Larimer County forester Dave Lentz said the trees are not likely to die because of beetle infestation. The beetle goes through a couple of generations each season, one in the spring and another in late summer. It is during these times that the beetle feeds on elm leaves and causes the trees to look unhealthy.

Colorado State University plant diagnostician Tamla Blunt said the beetle has reappeared in Windsor, but could not confirm sightings in Wellington.
Yet, a drive around town tells the story.

For a long time, elm leaf beetles were common in the area, but during the last 20 years they have not been prevalent in Northern Colorado. According to a fact sheet written by CSU Prof. Whitney Cranshaw, repeated infestations weaken the trees and make them vulnerable to branch die-back and wind injury.

As the days shorten in late summer, beetles stop producing eggs, feed for a while and then seek shelter for the winter. Long winters or a late spring freeze will kill large numbers of beetles. They can be controlled by insecticides applied to the soil or by banding trees with an insecticide.
Beetles can become a serious nuisance when they enter homes to overwinter.

While they do not feed or reproduce when indoors, they become active in late winter and spring and can be found crawling on windows and furnishings.
To prevent infestations of beetles in homes, seal all cracks and caulk around window molding and under siding. Vacuum regularly, especially during warm periods when the beetles are active and gather on windows or walls.
Insecticide application to the exterior of a building can be effective.

These beetles do not damage household foods or furnishings. Problems end by mid-spring when the beetles head for the outdoors or die.

Lentz describes Siberian elms as “weed trees” prone to grow in harsh areas. Pioneers planted them as windbreaks and they are known to self-seed heavily. It is no longer legal to plant Siberian elms in Fort Collins.

According to Lentz, the American elm, a particularly attractive tree, has been a primary target of the elm leaf beetle. Over time, the insect has caused the demise of most American elms. European and Rock elms are also prized and are sometimes treated in order to kill attacking elm leaf beetles.

They may not be so beautiful, but the Siberian elms in Wellington continue to provide shade and are likely to do so for a long time to come.