The rate of development of each of the developmental stages of summer fruit tortrix moth is only completed when a specific heat sum has accumulated. The specific heat sums are known and can be calculated each day from the daily maximum and minimum air temperature. The forecasting model PESTMAN can be used to give approximate predictions of the timing of occurrence of each of the life stages of the pest.
Forecasting the time that overwintered caterpillars reach the last instar stage (for timing Insegar sprays)
- Overwintered larvae reach the last instar development stage approximately 75‑100 day-degrees C above a threshold temperature of 8oC starting from 1 January.
Forecasting the start and peak of first generation adults
- The start and peak of the flight of first generation adult moths occurs approximately 170 and 210 day-degrees C above a threshold temperature of 10oC after 1 January.
Forecasting the start and peak of second generation adults
- The start and peak of the flight of second generation adult moths occurs approximately 616 and 693 day-degrees C above a threshold temperature of 10oC after 1 January.
Forecasting the timing of egg hatch
- Egg development takes approximately 103 day-degrees C above a threshold temperature of 8.6oC.
- The percentage egg development that accrues at various daily maximum and minimum air temperatures is given in the look-up table.
- Sum the daily percentage egg development amounts starting from the day the first pheromone trap catch of 5 or more moths occurred.
- Apply the first egg hatch spray when the temperature sum reaches 90-100%.
- If above threshold catches continue for more than one further week, a second spray may be necessary 7-10 days later.