The European Elm scale is a soft scale that is found primarily on elm trees. Severe infestations can reduce tree vigor and cause branch die-back. The European Elm Scale Growing Degree Day Model can help to predict the timing of different life cycle stages.

European Elm Scale Life Cycle Stages

European Elm Scales overwinter as 2nd instar nymphs in bark or twigs. Egg hatch typically occurs in summer and crawlers move around and feed before settling on the undersides of leaves.

The periods of crawler emergence is key for insect prevention, if necessary. Researchers have created the European Elm Scale Emergence Growing Degree Day Model to better predict when the adults will emerge.

Calculating Growing Degree Day Units

The European Elm Scale Emergence Growing Degree Day model uses a lower threshold of 51.8F. It can be calculated with daily high and low temperatures, using the sine model to estimate growing degree day units, or the Pest Prophet app can be used to calculate GDD accumulation from hourly temperature data for a specific field.

Using Mar. 1st as a default “biofix” date, or starting point for accumulation. Peak crawler emergence occurs approximately at  542 GDD(F). This can be used an approximate target for beginning treatments.

Source:

Dreistadt, S. H. and K.S. Hagen. 1994. European elm scale (Homoptera: Eriococcidae) abundance and parasitism in northern California. Pan-Pacific Entomologist 70:240-252.