EUROPEAN ELM SCALE

European elm scale is a destructive pest that feeds on American elm trees throughout Alberta, though it is worse in the South. It first became a problem in Calgary about 20 years ago, and is now city-wide. Red Deer currently has a growing scale problem, mainly due to untreated City trees harboring and spreading the insects.

Elm scale is characterized by “weeping” trees in June, as a result of honeydew excreted by the insects. Homeowners often notice their vehicles covered in sticky residue, and outdoor patios and walkways often turn black with sooty mold that grows on the honeydew.  Elm twigs and branches appear blackened, the leaves and buds are often smaller than normal, and within one to two years after infestation, small branches begin to die. Untreated, entire trees can suffer a slow death.

Treatment is by direct trunk injection and is very effective in controlling or eliminating the pest within a couple of seasons, depending on the level of infestation. The timing is from the end of May until the end of August.