LOW TEMPERATURE PHOSPHINE FUMIGATION FOR POSTHARVEST PEST CONTROL ON FRESH VEGETABLES

Authors: Liu, Yong Biao

Submitted to: Proceedings of International Research Conference on Methyl Bromide Alternatives
Publication Type: Proceedings
Publication Acceptance Date: 9/10/2009
Publication Date: 11/10/2009
Citation: Liu, Y. 2009. LOW TEMPERATURE PHOSPHINE FUMIGATION FOR POSTHARVEST PEST CONTROL ON FRESH VEGETABLES. Proceedings of International Research Conference on Methyl Bromide Alternatives.

Interpretive Summary: Small scale fumigation treatments and one commercial scale container fumigation treatment were conducted to determine efficacy and safety of low temperature phosphine fumigation treatment for control of western flower thrips on exported lettuce, broccoli, asparagus, and strawberries for Taiwan market. Western flower thrips was very susceptible to low temperature phosphine fumigation treatment. Total thrips control was achieved in =18 hour fumigation treatments with =250 ppm phosphine. One day fumigation treatments with phosphine were tested on all products. For all the products, there were no significant differences between the treatments and the controls in postharvest quality and there were no injuries caused by the fumigation treatments. In the commercial scale low temperature phosphine fumigation trial, head lettuce, romaine lettuce, asparagus, and strawberries together with thrips on infested lettuce plants were subjected to 18 hour fumigation at 2.4°C. Complete control of the thrips was achieved. The quality of the treated products was evaluated treatment after the products had been stored for certain lengths of time and the low temperature phosphine fumigation treatment had no negative impact on product quality. One day after the end of fumigation treatment, phosphine level was below the detectable limit of 0.01 ppm. The study confirmed the efficacy and safety of low temperature phosphine fumigation found in the small scale tests and also suggested that practical use in refrigerated shipping containers is feasible with certain modifications.

Technical Abstract: U.S. exported lettuce, broccoli, asparagus, and strawberries often harbor western flower thrips (Frankliniella occidentalis), a quarantined pest in Taiwan, and therefore require quarantine treatment. Fumigation with pure phosphine at a low temperature of 2°C was studied to control western flower thrips and to determine effects on the quality of the treated products. Total thrips control was achieved in =18 hour fumigation treatments with =250 ppm phosphine. One day fumigation treatments with phosphine were tested on all products. For all the products, there were no significant differences between the treatments and the controls in postharvest quality and there were no injuries caused by the fumigation treatments. A commercial scale low temperature phosphine fumigation trial for control western flower thrips on head lettuce, romaine lettuce, asparagus, and strawberries was also conducted in a 40’ reefer container. Fumigation treatment was conducted at 2.4°C for 18 hours with 320-940 ppm pure phosphine gas from a pressurized cylinder. The treatment was terminated with four intermittent 30 min aerations with one container door opened separated by 30 min with container doors closed. By the end of aeration, phosphine level in the container dropped to 0.22 ppm measured with phosphine detector tubes. After fumigation treatment, fresh air exchange for the container was set for lettuce shipping and products were stored in the container for four days to monitor phosphine residue in the container. One day after the end of fumigation treatment, phosphine level was below the detectable limit of 0.01 ppm. Quality of strawberries was evaluated one day and 7 days after fumigation treatment and quality of asparagus was evaluated 2 days and 8 days after the treatment. Broccoli quality and lettuce quality was evaluated 2 weeks after the fumigation. There were no negative effects on any of the products by the fumigation treatment. Thrips mortality was scored after lettuce was unloaded from the container 4 days after fumigation. Complete mortality of thrips was achieved. In conclusion, we achieved the objectives of validating efficacy and safety of low temperature pure phosphine fumigation treatment in a commercial scale container trial for control of western flower thrips on head lettuce, romaine lettuce, broccoli, asparagus, and strawberries. Latest progress on practical use of low temperature phosphine fumigation under insolated cover was also presented and discussed.