Elm Leaf Miner

Are your elm trees looking a little sad this summer? You’re not alone. Across the Denver area this time of year, many an elm (American and Siberian) are displaying yellowing and brown, blotchy leaves. While it’s not an encouraging sight, fear not because it is not necessarily fatal. These symptoms are commonly a result of elm leaf miner, or Kaliofenusa ulmi if you want to impress your friends. In its adult form, the miner is a stout black wasp but the brown or yellow serpentine and then blotchy patches seen on leaves are a result of the larvae.

The miner spends the winter as a full grown larvae beneath the soil of a previously infested elm tree and adults form in late winter. Once new leaves emerge on elms in the spring, the adult females lay eggs by inserting them into the middle of the leaves. A keen eye can detect this by noting small, white spots present on leaves in May. Once hatched, the larvae develop, causing the serpentine mines between the surface layers of the leaves that eventually bleed into one another to cause the blotchy effect. If you happen to pick up one of these leaves off of the ground in early- mid summer, notice that these blotches are full of dark powdery substance. This is frass produced by the miner larvae as they feed. Once mature, they’ll cut through these papery blotches, dropping to the ground to tunnel and form cocoons to repeat the life cycle all over again.

Photo C/o Whitney Cranshaw, Colorado State University, Bugwood.org

Colleen oakes, qs