The Holly Leafminer (Phytomyza ilicis) is an important pest on European Holly in many regions. Overwintered Holly Leafminer pupae typically emerge as adults in spring and begin to lay eggs.  Researchers have developed a model, and available on the Pest Prophet app,  to predict adult emergence, then later larvae emergence, based on 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 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. First adult emergence occurs between 192-246 GDD(F) and larvae emergence occurs between 247-448 GDD(F). These larvae can be targeted for treatment by 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.