A mass hatch of the eggs of mussel scale often occurs in a short time period of a few days in late May or June.
- Insecticide sprays need to be targeted against the young crawlers that emerge.
- Mature larvae are protected by their outer scale and are much less susceptible to insecticides.
- For this reason, pinpointing the timing of the mass hatch is helpful to time sprays correctly.
- The timing of the hatch and the optimum timing for application of sprays can be predicted from temperature sums.
- First emergence occurs at 151 day-degrees above a threshold of 8oC after 1 January.
- Mass egg hatch occurs at about 190 day-degrees. 90% hatch occurs at 230 day-degrees and is considered to be the optimum timing for application of commonly used pesticides.
- Early hatched nymphs may reach the second instar stage by this time but these are still susceptible to the commonly used insecticides.