The Lilac / Ash Borer is a wood-boring moth that can affect a variety of hosts. The first symptoms are frass mixed with sap at the entry point of larvae into the tree. Adult Lilac /Ash Borers are moth that can resemble wasps.

Lilac Borer Life Cycle Stages

Lilac Borers usually take one year to complete a generation. Lilac Borers overwinter as larvae in the tree, and resume feeding activities spring or late winter. These larvae then pupate and adults emerge in late spring or early summer. Adults then feed and reproduce.

The period of adult emergence is key for insect prevention, both for placing traps and for using insecticides, if necessary. Researchers have created the Lilac Borer Adult Emergence Growing Degree Day Model to better predict when the adults will emerge.

Calculating Growing Degree Day Units

The Lilac Borer Emergence Growing Degree Day model uses a lower threshold of 50F. 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 Jan. 1st as a default “biofix” date, or starting point for accumulation, the first adult emergence occurs at approximately 305 GDD (F) and peak at approximately 930 GDD (F). This can be used to guide pest management decisions and timing.

Source:

Potter, D. A. and G. M. Timmons. 1983. Forecasting emergence and flight of the lilac borer (Lepidoptera: Sessiidae) based on pheromone trapping and degree-day accumulations. Environ. Entomol. 12: 400-403.