The Western Spruce Budworm (Choristoneura occidentalis)  is an important pest on pine and spruce trees. Overwintered Western Spruce Budworm larvae typically emerge in spring and the first adults may be seen soon after. Insecticide treatments targeting 1st generation larvae are typically the best way to control Western Spruce Budworm populations for the entire growing season. Western Spruce Budworm Growing Degree Day Model, developed by researchers at Cornell University, and available on the Pest Prophet app, is a tool growers can use to predict larvae emergence based on field-specific temperature data.

Initiating the Biofix

To properly use the model, the biofix must first be set. This is the date that will serve as the starting point for growing degree day accumulation. For this type of model January 1st is the standard biofix to start accumulation (for the Northern Hemisphere). This can be used to predict when adults will emerge and pheromone traps can be used.

After adults are observed and confirmed, the biofix can be adjusted in order to improve accuracy of the model for predicting later life stages.

Growing Degree Day Accumulation and Treatment

After the biofix is set, growing degree day accumulation can begin, using a lower threshold of 50F. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. Larvae typically emerge between 200 GDD (F) and 300 GDD (F) after the Jan. 1st biofix. These larvae can be targeted for insecticide treatment.

Source:

Kowalsick, Thomas, and Scott Clark. 2006. Using Growing Degree Days for Insect Pest Management. Cornell Cooperative Extension. 2006.