Most fruit growing regions in WA experience at least a partial third CM generation each year. Moths representing a third flight emerge in late August or early September and deposit eggs. Though a portion of these CM will not complete their lifecycle, the potential impact of this generation should not be underestimated. If left uncontrolled, third generation CM larvae will be feeding in the orchard just before harvest, which could result in unwanted fruit injury. Further, some third generation CM larvae may overwinter and contribute to the CM population that emerges the following spring.
We have developed a formula to calculate the percentage of third generation egg hatch that will occur based on the correlation between degree days (DD) on 15 August and 1 November. This correlation can be used to predict the potential impact of the third generation so that necessary controls can be planned accordingly. DAS provides these automatically updated predictions of third generation CM egg hatch after 15 August in the CM model output. Check in regularly as the third generation estimates become more accurate as we get closer to 1 November.
(Ute Chambers & Vince Jones, WSU-TFREC)