Written by Matthew Jones, Entomology Research Assistant Professor and WSU-DAS Manager, WSU Tree Fruit Research and Extension Center, Wenatchee, WA Nov 2020.
Codling moth larvae that will overwinter leave the fruit in the fall, around harvest, and seek overwintering sites. Once they find a location, they spin a protective hibernaculum (cocoon) that provides shelter until spring when the larvae pupate and develop into adults. These shelters usually occur within the rough bark of the tree or on orchard floor debris However, bins used during harvest are known to harbor diapausing codling moth larvae. The larvae enter the bins during the time leading up to harvest when the bins are in the orchard. Higbee et al. (2001) found that larvae frequently used surface irregularities on wood bins or bored short tunnels (2-4 cm) into the wood for pupation. No evidence of excavation in plastic bins was observed, but larvae would colonize the open areas between the structural fins located on the underside of the bins. To summarize, codling moth larvae colonize harvest bins made of wood far more often than plastic.
Why is this important?
Codling moth larvae developing in bins are important for 2 main reasons:
- Bins are frequently moved to different locations, so moths can be spread from or into an infested orchard block.
- Larvae developing in bin piles can disrupt monitoring and management of codling moth. Depending on where within the bin pile moths are developing, individuals will experience different temperatures, driving them to develop at different rates. Lower bins remain colder, causing slower moth development and later emergence. Delayed moth emergence from bins creates overlapping generations that reduces the ability to spray at critical generational timings. Overlap from bins is a major reason why trap catches often do not agree with phenology models.
How to manage bins
First, using plastic bins for harvest will greatly mitigate bin infestation by codling moths. Second, sterilize bins before they go back out to orchards. While there are no materials registered for spraying bins, bins can be run through a “bin cooker” to sterilize them at the warehouse, before returning to the field. Third, minimize the number of time bins are in the orchard: i.e. do not bring them into the orchard until right before harvest. If that is not practical for your operation, construct small, separated bin piles in narrow lines to reduce the temperature insulating effect.
References
Higbee, B. S., Calkins, C. O., & Temple, C. A. (2001). Overwintering of codling moth (Lepidoptera: Tortricidae) larvae in apple harvest bins and subsequent moth emergence. Journal of Economic Entomology, 94(6), 1511-1517.
Contact
Matthew Jones
Research Assistant Professor
Manager/Educator WSU Decision Aid System
TFREC, Wenatchee, WA
email: matthew.s.jones@wsu.edu
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