The Spotted Tentiform Leafminer (Phyllonorycter blancardella) is an important pest on apples in a variety of areas. Overwintered Spotted Tentiform Leafminer larvae typically emerge from fallen leaves in spring and the first adults may be seen soon after. There can be 2-3 generations in a year, depending on the weather. Insecticide treatments targeting adults, pre-egg laying are typically the best way to control Spotted Tentiform Leafminer populations for the entire growing season. The Spotted Tentiform Leafminer Growing Degree Day Model, developed by researchers, and available on the Pest Prophet app, is a tool growers can use to predict egg hatch based on adult trap catches and 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, the date of peak adult catch for the generation of adults from overwintered larvae is used. This date can be used to predict when the next generation of adults will emerge and insecticides 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 44.1F and an upper threshold of 86F. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. Next generation of Adults typically emerge at 760 GDD (F) after the biofix, and the next generation after that at 1247 GDD (F) after the original biofix date.

Source:

Rock, G. C., R. E. Stinner, J. E. Bacheler, L. A. Hull, and H. W. Hogmire, Jr. 1993. Predicting geographical and within-season variation in male flights of four fruit pests. Environ. Entomol. 22: 716-725.