Do you have elm trees near or around your home that seem to think it’s fall already? Are their leaves brown in color, lacey in their appearance and prematurely falling to the ground? Elm trees, especially Siberian elms, are host to two leaf-feeding insects, elm leaf beetle and elm leaf miner, that, combined, are causing concern for residents on the Front Range.

Elm leaf miner is a common insect that skeletonizes the leaves, and causes the leaves to prematurely brown and fall to the ground. Typically, the damage from this insect pest is mostly aesthetic and limits our ability to enjoy the dark green leaves of the tree throughout the growing season.

Elm leaf beetle is a trickier pest. In the 1980s and 1990s, the elm leaf beetle was another common aesthetic leaf feeding pest, however  it reappeared during the summer of 2020 and now tag teams the feeding of leaves on Siberian elms. Elm leaf beetle can be more of an issue than elm leaf miner in that it actually has two life cycles a year, producing two phases of larva and beetles in a single season.

The Colorado State University Extension advises that, although the insects defoliate the trees, there is minimal long-term health effects on the Siberian elms, thus treatment is not necessary to maintain tree health. However, the insects are certainly a nuisance. Elm leaf beetle commonly seeks shelter in homes to survive the winter months and emerges from homes in the spring to feed and reproduce. Similar to other home invading insects, you should evaluate the seals around windows and doors to reduce the number of beetles entering your home.

At this time the City of Longmont is aware of the issues related to elm leaf beetle and elm leaf miner, but has no plans to treat City owned and maintained Siberian elm trees. Treatment options are available for private trees and guidance can be found through the Colorado State University Extension. City of Longmont Licensed Tree Contractors can help you make a decision if treatment is an option for your tree.

Photos courtesy: Whitney Cranshaw, Colorado State University, Bugwood.org