Omnivorous Leafroller (Platynota stultana) is an important pest on grapes and stone fruit in California and other locations. Overwintered larvae typically emerge in late winter/ early spring and the first adults may be seen soon after. There can be 4-6 generations in a year, depending on the weather. Insecticide treatments targeting 1st or 2nd generation larvae are typically the best way to control Omnivorous Leafroller populations for the entire growing season. The Omnivorous Leafroller 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 Omnivorous Leafrollers, 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 48F and an upper threshold of 87F. 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 500 GDD (F) after adult moth catch and the larval stage will be between 700 and 900 GDD (F), which is the optimum timing for a single insecticide treatment. After 1169 GDD (F) the next generations of adults will be seen in flight.

Adjusting Biofix for Each Generation

For best results in subsequent generations, the biofix should be reset when new pheromone traps are placed to capture adult moths. In many cases, 1st generation larvae may be mostly found on weeds or cover crops, and treating the 2nd generation will have the most success. In cases of high Omnivorous Leafroller population pressure, or if flight from nearby fields has occurred, treating the 3rd generation may be necessary. For these these generations, between 700 and 900 GDD(F) following the readjusted biofix is the optimum time for insecticide treatment.

Source:

Kido, H., D. L. Flaherty, W. W. Barnett and H. L. Andris. 1982. Omnivorous Leafroller. IN: Grape Pest Management. U.C. Div. Agr. Sci. Publ. #4105. pp. 126-136.