Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2010
Publication Date: 2/1/2011
Citation: Liu, Y. 2011. Semi-commercial ultralow oxygen treatment for control of western flower thrips, frankliniella occidentalis (thysanoptera: thripidae), on harvested iceberg lettuce. Postharvest Biology and Technology. 59: 138-142.
Interpretive Summary: Pallet scale ultralow oxygen (ULO) treatment was conducted to control western flower thrips, Frankliniella occidentalis (Pergande), on head lettuce which had been stored for various lengths of time ranging from 1 to 6 days. The ULO treatment with 0.003% O2 was conducted at ambient temperature of 10°C for two days. The purpose was to determine the minimum storage time before ULO treatment for preventing injury to lettuce heartleaves by the ULO treatment and develop protocols for large scale ULO treatment which could be expanded for commercial use. Complete control of the thrips was achieved. Three of seven cultivars of fresh lettuce which experienced one day storage before ULO treatment sustained injury to heartleaves. Lettuce which experienced 3, 4, and 6 days of cold storage showed no increases in heartleaf injury as compared with untreated controls. This study demonstrated that three day exposure to cold storage before ULO treatment increased tolerance of lettuce and prevented injury to heartleaves by the ULO treatment. The treatment protocols have potential to be extended to large scale commercial use of ULO treatment for control of western flower thrips on exported lettuce.
Technical Abstract: Pallet scale two day ultralow oxygen (ULO) treatment with 30 ppm oxygen at 10°C ambient temperature was conducted on seven cultivars of vacuum cooled iceberg lettuce which had been stored for 1, 3, 4, and 6 days to develop a safe and effective treatment for control of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Complete control of thrips was achieved in all three pallet tests. Temperature of lettuce increased from about 5°C at the start of ULO treatment to 9.6°C at the end of the treatment. Fresh vacuum cooled lettuce from 3 of 7 cultivars sustained injuries to heartleaves by the ULO treatment. However, lettuce which had been stored at low temperature for 3, 4, or 6 days before the ULO treatment tolerated the ULO treatment and there were no significant quality reduction compared with untreated controls. There were considerable variations among different lettuce cultivars in susceptibility to heartleaf injury by the ULO treatment. Heavier heads were significantly more prone to heartleaf injury than lighter heads. This study demonstrated that 3 day postharvest storage followed by 2 day ULO treatment was effective in controlling western flower thrips and safe to lettuce quality. The ULO treatment protocols developed in this study also has potential to be scaled up for commercial ULO treatment applications.