Ethyl Formate as a Methyl Bromide Alternative for Fumigation of Citrus: Efficacy, Fruit Quality, and Workplace Safety

Ethyl formate (EF) was evaluated as a potential alternative to methyl bromide (MB) for phytosanitary treatment of imported citrus fruit in the Republic of Korea. Planococcus citri (Risso) (Hemiptera: Pseudococcidae), a mealybug with known tolerance against EF and MB, was used as a representative pest to test efficacy of the two fumigants against eggs. In nine commercial-scale refrigerated container (67.5 m3) trials using imported orange, lemon and grapefruit, EF applied at the currently approved dose for citrus (70 g·m-3 at 5°C for 4 h, developed for Aspidiotus excisus Green (Hemiptera: Diaspididae), a species less EF tolerant than P. citri) resulted in 76.9–98.3% mortality of P. citri eggs. The EF treatment did not affect the sugar content or the color of peel and pulp of the treated fruit. When oranges were treated according to the current MB (64 g·m-3 at >5°C for 2 h) or EF treatment guidelines, the concentration of fumigant around the fruit fluctuated between 9.4 and 185.1 ppm for EF and 9.5–203.0 ppm for MB during the 72-h post-fumigation processes (venting [0–2 h], transportation to storage [2–24 h], and storage periods [24–72 h]) with both EF and MB maintained between 10 and 100 ppm during the storage period. Considering the efficacy of EF, its apparent lack of phytotoxicity, and its more manageable threshold limit value for humans (100 ppm EF compared to 1 ppm MB for an 8-h time weighted average exposure), our results suggest that EF may be a promising alternative to MB for the phytosanitary treatment of imported citrus in Korea.