Bin piles can be an outside source of codling moth (CM) populations. Bins that are brought into the orchard mid season can harbor overwintering CM larvae from the previous year. Because these CM are transported from outside the orchard (and often from cold storage buildings), their phenology will not be in sync with the internal orchard population. Therefore, CM adults emerge from bins at different times than predicted by the model.
In addition, emergence of adult CM from wooden bins placed in stacks is prolonged compared with the internal orchard population. This is due to temperature differences within the bin stacks from the top to the bottom. Bins on the bottom of a stack are exposed to the least amount of warming resulting in slower CM development and later adult emergence compared with bins on the top.
When do CM colonize bins?
The majority of CM enter the bins during the time that the bins are in the orchard before harvest. Wooden bins are preferred over injection molded plastic bins as the CM larvae are able to find more crevices to hide in wooden bins and penetrate the wood to build their hibernacula. Items made of wood, such as props used for supporting limbs or bins, are important overwintering sources for larvae. Larvae complete development in the fruit, then search for an overwintering site. These sites can provide overwintering substrates for CM entering diapause as early as June or July.
Monitoring, monitoring, monitoring
Extra pheromone-baited traps should be placed around bin piles to monitor moth emergence. Border sprays of 4-5 rows around external sources or bin piles may be necessary if these areas are identified as problems. A good monitoring program can help pinpoint these problem areas so that controls to protect fruit can be applied when necessary.
One way to minimize infestation of bins is be to place bins in the orchard as close to harvest as possible. In addition, few fruit packers have started to use hot water bath treatments to disinfest harvest bins from overwintering codling moth larvae.
Resources for this article:
- PMTP Newsletter – Monitoring codling moth http://pmtp.wsu.edu/newslettersV1I7.html#sec-4
- Higbee, B.S., C.O. Calkins, and C.A. Temple 2001. Overwintering of codling moth (Lepidoptera: Tortricidae) larvae in apple harvest bins and subsequent moth emergence. Journal of Economic Entomology 94: 1511-1517. (pdf)