The Rhododendron Borer (Synanthedon rhododendri) is an important pest on rhododendrons, and a few other hosts. Rhododendron Borers typically overwinter as larvae, then in spring they pupate and adults emerge. After emergence they can be targeted by traps or insecticide treatments. The Rhododendron Borer Growing Degree Day Model, developed by researchers, and available on the Pest Prophet app, is a tool growers can use to predict adult emergence in spring, as well as second generation adult emergence, later in the season.

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 the biofix date should be set to March 1st for the Northern Hemisphere.

Growing Degree Day Accumulation and Treatment

After the biofix is set, growing degree day accumulation can begin, using a lower threshold of 50F. Calculating growing degree days can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. Adult emergence occurs between 192-298 GDD(F). Second generation adults emerge between 1030-1400 GDD (F). These adults can be targeted with traps or insecticides.

Source:

Growing Degree Day Information. Nathan W. Siegert, Deborah G. McCullough and Jeffrey A. Andresen. Michigan State University, 2 October 2015. Web. 25 February 2016.

Using Growing Degree-Days for Insect Pest Management. Thomas Kowalsick and Scott Clark. Cornell Cooperative Extension in Suffolk County, March 2012. Web. 25 February 2016.