The Obliquebanded Leafroller Moth (Choristoneura rosaceana) is an important pest on nuts in California. Overwintered Obliquebanded Leafroller larvae typically emerge in late winter/ early spring and the first adults may be seen soon after. There can be 3 generations in a year, depending on the weather. Insecticide treatments targeting 1st or 2nd generation larvae are typically the best way to control Obliquebanded Leafroller populations for the entire growing season. The Obliquebanded Leafroller 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 Obliquebanded Leafrollers, this biofix is the first date of consistent, sustained adult moth catches using pheromone traps in the field. 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 85F. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. The the larval stage will be between 781and 1200 GDD (F). The optimum timing for a single insecticide treatment is approximately 1,000 GDD(F) after the adult moth catch. After 1201 GDD (F) the next generations of adults will be seen in flight.

Adjusting Biofix for Each Generation

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

Alternate Model for Hazelnuts

For Hazelnuts as a host, another growing degree day model has been developed and also available on the Pest Prophet App. It is used in the same way, but uses a lower threshold of 50 GDD (F) and an upper threshold of 90 GDD (F). Using this model, peak adult flight occurs at approximately 655 GDD (F).

Source:

Brunner et al. 1997. Leafroller models: predicting development and timing controls. Washington State University Cooperative Extension. AREAWIDE IPM UPDATE. Vol. 2, No. 7 – June 1, 1997

Gangavalli & AliNiazee, M. T. 1985. Temperature requirements for development of the obliquebanded leafroller, Choristoneura rosaceana (Lepidoptera: Tortricidae). Environ. Entomol. 14:17-19.