The Elm Leaf Beetle is a leaf-chewing pest on elm trees. In cases of severe infestation, trees may be defoliated.

Elm Leaf Beetle Life Cycle Stages

Elm Leaf Beetles overwinter as adults in bark crevices or woodpiles. In spring they fly onto leaves and begin to lay eggs. Larvae emerge and begin feeding on foliage before moving down the tree trunk.

The period of larvae emergence is key for insect prevention, because this is the time that trunk spray or bark bands should be applied for maximum effect. Researchers have created the Elm Leaf Beetle Adult Emergence Growing Degree Day Model to better predict when the adults will emerge from the soil.

Calculating Growing Degree Day Units

The Elm Leaf Beetle Emergence Growing Degree Day model uses a lower threshold of 51.8F  (11C).. 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, the first adult emergence from overwintering occurs at approximately 360 GDD (F). Peak larvae emergence occurs at approximately 701 GDD(F) which is the optimum time for insecticide treatment.

Source:

Elm leaf beetle. IN: Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. University of California Statewide IPM project. Div. Agr. Publ. #3359