The Orange Tortrix Moth (Argyrotaenia franciscana) is an important pest on grapes and citrus in California and other locations. Overwintered Orange Tortix larvae typically emerge in late winter/ early 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 1st or 2nd generation larvae are typically the best way to control Orange Tortix populations for the entire growing season. The Orange Tortrix Growing Degree Day Model, developed by researchers at the University of California, 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 Orange Tortrix Moths, this biofix is the first date of consistent, sustained adult moth catches using pheromone traps in the orchard or vineyard. Traps should be placed in early spring, or late winter, and checked on a regular basis. Once adult moths have been trapped for a few weeks in a row, the date of the first catch should be used as the biofix.

Growing Degree Day Accumulation and Treatment

After the biofix is set, growing degree day accumulation can begin, using a lower threshold of 43F and an upper threshold of 74F. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. The first egg hatch will occur at about 53 GDD (F) after adult moth catch and the larval stage will be between 296 and 949 GDD (F). The optimum timing for a single insecticide treatment is around 1000 GDD(F) after the adult moth catch. After 1216 GDD (F) the next generations of adults will be seen in flight.

Adjusting Biofix for Each Generation

For best results in second generation of Orange Tortrix moths in a given season, the biofix should be reset when new pheromone traps have successfully capture adult moths in late spring/ early summer.  1,000 GDD(F) following the readjusted biofix is, again, the optimum time for insecticide treatment.

Source:

Bettiga, L. J., H. Kido, and N. F. McCalley. 1992. Orange Tortrix. IN: Grape Pest Management. 2nd. Edition. U.C. Div. Agr. Sci. Publ. #4105.