Washington State University entomologist Dr. Vince Jones, has issued the following report.
Codling moth will have 3-4 generations at most sites in Eastern Washington this year.
This year is the hottest year on record at WSU-TFREC in Wenatchee since 1931 when record keeping began. The current codling moth DD (degree-days) accumulation on 28 July at TFREC (2274 DD) is 16.4% higher than 2014 (second hottest year on record) and 10.6 % higher than the previous hottest year (1958). The average DD accumulation over 1931-2015 was 1661 DD at this point, so we have accumulated 613 DD (36.9%) more than the average! Examining the DD accumulations throughout the eastern part of the state shows we are 7-13 days ahead of those in 2014 and the long range forecasts show that before diapause induction is complete on 18 August (diapause is triggered solely by photoperiod) that several sites in the warmer part of the state (e.g., Desert Aire, Mattawa, Parker, WSU Sunrise, and WSU Tri-Cities) will have accumulated >2800 DD, which will allow a substantial number of the second summer generation to skip diapause and will result in a fourth adult flight (the overwintering adults + 3 summer generations) and larvae being able to complete a partial third summer generation in the warmer areas. The difference between an “average” year and the current record-breaking one can be seen in the graph below (click graph to enlarge).
If you are using mating disruption, these extra flights should not cause problems unless you have a large external population migrating into your orchard. The mating disruption dispensers should not run out even though this is a hotter year.
If you are not using mating disruption, these late flights may cause fruit damage and need to be controlled if populations in your orchard are high. Controls for this generation need to be started by 2345 DD. Make sure you pay close attention to the pre-harvest intervals for the pesticide used and follow closely model predictions on das.wsu.edu to deal with the third summer generation larvae.
View this news item at the Good Fruit Grower.