The Southern Red Mite (Oligonychus ilicis) is an important pest on a variety of hosts, including azaleas and rhododendrons. Southern Red Mites typically emerge in spring from overwintered eggs. After emergence they can be targeted by traps or insecticide treatments, or a dormant treatment may be given before emergence. The Southern Red Mite Growing Degree Day Model, developed by researchers, and available on the Pest Prophet app, is a tool growers can use to time dormant treatment and to predict adult emergence from overwintered eggs and subsequent generations.

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. 8-92 GDD (F) is recommended for dormant treatment. First adult emergence occurs between 246-363 GDD(F), with the following generation adult emergence occuring between 618-802 GDD(F) and 2500-2700 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.