Peach Twig Borer (Anarsia lineatella) is an important pest on peach and other stone fruit crops in California and many other regions. Overwintered Peach Twig Borer larvae typically emerge in late winter/ early spring and the first adults may be seen soon after. There can be 3-4 generations in a year, depending on the weather. Insecticide treatments targeting 1st or 2nd generation larvae are typically the best way to control Peach Twig Borer populations for the entire growing season. The Peach Twig Borer Growing Degree Day Model, developed by researchers at University of California Davis, 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 Peach Twig Borers, this biofix is the first date of consistent, sustained adult moth catches using pheromone traps in the orchard. 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 50F and an upper threshold of 88F. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. The optimum timing for a single insecticide treatment targeting larvae is approximately 300-350 GDD(F) after the adult moth catch, with a follow up spraying (if using Bacillus thurengiensis) at approximately 450 GDD (F). After 400 GDD (F) shoot strikes will first appear and should be monitored for.

Adjusting Biofix for Each Generation

For best results in second generation of Light Brown Apple moths in a given season, the biofix should be reset when new pheromone traps have successfully capture adult moths in late spring/ early summer. Approximately 300 GDD(F) following the readjusted biofix is, again, the optimum time for insecticide treatment.

Source:

Rice, R. E., F. G. Zalom, and J. F. Brunner. 1982. Monitoring peach twig borer development with degree-days. U.C. Div. Agr. Pub. #21302.