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

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 23-kg bags of in-shell walnuts (Juglans regia). Consistent with the approved parameters, in-shell walnuts with nut meat temperature (T) of 15.4 ± 0.2 °C (grand mean ± 2 SD; x‾GM± 2spooled) 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 MB at ca. 13.3 KPa (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 23-kg bags or sealed fiberboard cartons. •Certain countries require control of codling moth in California walnuts.•Postharvest methyl bromide vacuum fumigation of walnuts packaged in bags is approved by Korea.•The approved fumigation results in a Ct exposure adequate to control codling moth.•Packaging in fiberboard cartons versus bags did not affect sorption, and in turn, the Ct exposure.