Low temperature fumigation of harvested lettuce using a phosphine generator

Authors: Liu, Yong Biao

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2018
Publication Date: 2/28/2018
Citation: Liu, Y. 2018. Low temperature fumigation of harvested lettuce using a phosphine generator. Journal of Economic Entomology. 111(3):1171-1176. https://doi.org/10.1093/jee/toy038.
DOI: https://doi.org/10.1093/jee/toy038

Interpretive Summary: A research scale phosphine generator from United Phosphorus Ltd was studied to determine whether a phosphine generator can be used to conduct low temperature phosphine fumigation on lettuce. Fumigations of 24 h were conducted to control western flower thrips and 72 h fumigations were conducted to control lettuce aphid. In addition, 48 h oxygenated phosphine fumigations in 60% O2 atmosphere were also conducted to control lettuce aphid. The generator was able to finish generating phosphine in 60-90 minutes. Complete controls of thrips in the 24 h fumigation was achieved. Complete control of lettuce aphid was also achieved in the 48 h oxygenated phosphine fumigation and in the 72 h normal phosphine fumigation. Lettuce quality was evaluated 2 weeks after fumigation. The 24 and 48 h fumigations did not have any impact on lettuce quality. But the 72 h fumigations caused brown stains on lettuce leaves. The damage was due to accumulation of CO2 and was consistent with long term fumigation with cylindered pure phosphine. This study demonstrated that phosphine generator has potential to be used to conduct low temperature phosphine fumigation to control pests on fresh products.

Technical Abstract: A research-scale phosphine generator, QuickPHlo-R, from United Phosphorus Ltd. (Mumbai, India) was tested to determine whether it can be used for low temperature fumigation and oxygenated phosphine fumigation of harvested lettuce. Vacuum cooled iceberg and romaine lettuce were fumigated in 442L chambers at 2°C for 24 h and 72 h for control of western flower thrips and lettuce aphid. Oxygenated phosphine fumigation for 48 h under 60% oxygen was also conducted at 2°C with iceberg and romaine lettuce for control of lettuce aphid. The generator produced sufficient phosphine for fumigation in 60-90 minutes. Complete control of western flower thrips was achieved in 24-h treatment, and the 48-h oxygenated fumigation and 72-h fumigation treatments under the normal oxygen level completely controlled lettuce aphid. Lettuce quality was evaluated 14-d after fumigation. There was increased incidence of brown stains on fumigated iceberg lettuce, and the increases were more obvious in longer (48 h) treatments. Iceberg and romaine lettuce from the 24 and 48-h treatments and controls exhibited very good visual quality even though there was significantly higher brown stain incidence on fumigated iceberg lettuce in all three treatment regimes, and also significantly lower internal quality score for iceberg lettuce in the 48 h treatment. The brown stains were likely due to the high sensitivity of lettuce to carbon dioxide. The study indicated that QuiPHlo-R phosphine generator has potential in low temperature phosphine fumigation due to the quick establishment of desired phosphine levels, efficacy in pest control, and reasonable safety to product quality.