Reducing Injury of Lettuce from Phosphine Fumigation

Abstract

Fumigation with cylindered pure phosphine free of ammonia has been used commercially at low temperatures in recent years to control pests on harvested fresh fruit and vegetables. However, long fumigation treatments cause injuries to lettuce (Lactuca sativa) and prevent its commercial use on lettuce. We evaluated whether absorbents for carbon dioxide (CO2) and ethylene can prevent injuries to lettuce in phosphine fumigation, hypothesizing that an accumulation of CO2 or ethylene be responsible for the injuries. Head and romaine lettuce were fumigated in chambers in the presence or absence of CO2 and ethylene absorbents for 3 days at 2 °C. The use of absorbents prevented lettuce injury associated with fumigation and resulted in higher lettuce quality. In the absence of the absorbents, both head and romaine lettuce sustained significant injuries in the form of brown stain, a typical symptom of CO2 injuries, and significantly reduced quality as compared with fumigation in the presence of absorbents. The injuries were likely caused by CO2 based on the facts that injuries were identical to CO2 injuries and the prevention of the injuries by the use of CO2 absorbent. The findings of this study have important implications for developing safe and effective phosphine fumigation protocols at low temperature for controlling insect pests on fresh commodities, especially when a long treatment time is required.