The Plum Fruit Moth (Grapholita funebrana) is an important pest on many varieties of stone fruit and other hosts. Overwintered Plum Fruit Moth larvae typically emerge in late winter/ early spring and the first adults may be seen soon after. There can be 1-3 generations in a year, depending on the weather. Insecticide treatments targeting 1st or 2nd generation larvae are typically the best way to control Plum Fruit Moth populations for the entire growing season. The Plum Fruit Moth Growing Degree Day Model, developed by European 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 Plum Fruit 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 50F. 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 peak at approximately 19 GDD (F) after adult moth catch and the larval stage will be between 154 and 469 GDD (F). The optimum timing for a single insecticide treatment is approximately 300(F) after the adult moth catch. After 757 GDD (F) the next generations of adults will be seen in flight.

Adjusting Biofix for Each Generation

For best results in second generation of Plum Fruit 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 350 GDD(F) following the readjusted biofix is, again, the optimum time for insecticide treatment.

Source:

Charmillot, P-J. R. Vallier and S. Tagini-Rosset. 1979. Plum fruit moth (Grapholitha funebrana Tr.): study of the life cycle in relation to the sums of temperature and considerations on the activity of the adult moths. Bulletin de la Societe Entomologique Suisse 52: 19-33.