The Omnivorous Leaftier (Cnephasia longana) is an important pest on some nut trees, in the Pacific Northwest and other regions. Overwintered Omnivorous Leaftier larvae typically emerge in late winter/ early spring and the first adults may be seen soon after. Thereis typically only generation per year. The Omnivorous Leaftier Growing Degree Day Model, developed by researchers, and available on the Pest Prophet app, is a tool growers can use to predict adult 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 Omnivorous Leaftiers, this biofix is usually set to January 1st for the Northern Hemisphere. Once larvae have been observed, the date of the first catch can be used to reset the biofix, and improve accuracy of later predictions.

Growing Degree Day Accumulation and Treatment

After the biofix is set, growing degree day accumulation can begin, using a lower threshold of 36F and an upper threshold of 100F. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. The first instar larvae will emerge at about 437 GDD (F). Pupation begins at approximately 1698 GDD (F).  Adult moths will occur at approximately 2045 GDD after the Jan. 1 biofix date. Traps and mating disruption pheromones should be placed to coincide with adult moth flight stages. Egg hatch for the next generation will occur at approximately 2765 GDD (F).

Source:

Coop, Len. 2012. Oregon State University. Omnivorous Leaftier Phenology (degree-day) Model. data from 1930-42, 46-51.