Navel Orangeworm (Amyelois transitella) is an important pest on many fruit and nut crops including: Almonds, figs, pomegranates, and walnuts are also major hosts. The first signs of an damage are small hole in the nut hull. The worm feeds on the nut from the inside and can cause major economic losses. In addition to directly causing losses, Navel orangeworm can also damage pistachios indirectly through fungal organisms that produce aflatoxins.

There can be multiple generations in a year, depending on the weather. In addition to orchard sanitation to prevent overwintering sites, insecticide treatments targeting 1st or 2nd generation larvae are typically the best way to control Navel Orangeworm populations for the entire growing season. The Navel Orangeworm 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 Navel Orangeworms, 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 55F and an upper threshold of 93.9F. This can be done using daily high and low temperatures, or using hourly temperature data using the Pest Prophet app. If eggs are laid in nut “mummies”, the next generation of adults and egg -laying will occur at approximately 1093 GDD(F) after the biofix, and this can be used for egg-targeting insecticides. For new crops, this will occur at approximately 739 GDD(F) after the biofix date.

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.

Source:

Sanderson, J. P., M. M. Barnes, and W. S. Seaman. 1989. Synthesis and validation of a degree-day model for navel orangeworm (Lepidoptera: Pyralidae) development in California almond orchards. Environ. Ent. 18: 612-617.