Methyl bromide vacuum fumigation of California USA in-shell walnuts packaged in fiberboard cartons

Authors: RODRIGUEZ, MATTHEW - University Of California, Davis; Tebbets, John; Walse, Spencer

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2021
Publication Date: 9/22/2021
Citation: Rodriguez, M., Tebbets, J.S., Walse, S.S. 2021. Methyl bromide vacuum fumigation of California USA in-shell walnuts packaged in fiberboard cartons. Journal of Stored Products Research. 94. Article 101879. https://doi.org/10.1016/j.jspr.2021.101879.
DOI: https://doi.org/10.1016/j.jspr.2021.101879

Interpretive Summary: Korea is a key buyer of in-shell walnuts from California, USA, which have been shipped in 50-lb bags for over 20 years. Due to consumer complaints regarding cracked shells, importers recently requested that the nuts be shipped in fiberboard cartons in an effort to reduce cracking. To make such a change, USDA must demonstrate to Korean authorities that this change in packaging will not compromise the ability for the required treatment to control codling moth. Results of the research demonstrate that the in-shell nuts will continue to arrive in Korea at the same level of security, even if packaged in fiberboard cartons.

Technical Abstract: Postharvest vacuum fumigation with methyl bromide (MB) was approved by Animal and Plant Quarantine Agency (APQA), Republic of Korea, to control codling moth, Cydia pomonella (Lepidoptera, Tortricidae), infesting 50-lb bags of in-shell walnuts. Consistent with the approved parameters, in-shell walnuts with nut meat temperature (T ) of 15.4 ± 0.2 °C (59.7 ± 0.4 °F ) ( ± 2s pooled) were packaged in sealed fiberboard cartons, loaded to 53% (v/v) chamber capacity, and fumigated in triplicate trials involving a single 63-carton pallet, with each lasting 4 h following the application of 56 mg L-1 (3.5 lbs/1000 ft3) MB at ca. 100 mmHg. MB concentrations were measured at four different locations over the course of each fumigation, respective Ct exposures were calculated, and the relative distribution of fumigant was evaluated. Exposures were maintained = ca. 75 mg L-1 h in all cases, resulting in Ct exposures sufficient to control codling moth. A single 18-pallet confirmatory trial involving sealed fiberboard cartons was then conducted at a commercial facility, gas measurements were taken as above, and a minimum Ct of 117 mg L-1 h was observed. A kinetic model of MB sorption was used to demonstrate congruence across all trials, thereby supporting the reproducibility, scalability, and efficacy of this treatment, regardless if the in-shell walnuts are packaged in 50-lb bags or sealed fiberboard cartons.