Abstract

Ethyl formate is a volatile compound which occurs naturally in a variety of products and is generally recognized as safe (GRAS) by the USA Food and Drug Administration (FDA). High concentrations have shown insecticidal properties and it is used as a GRAS fumigant of dried food. Ethyl formate is under investigation as an alternative to replace methyl bromide for quarantine fruit fumigation. However, ethyl formate can induce phytotoxicity in the fruit, limiting its potential use in the future. Concentrations and exposure times of ethyl formate were evaluated in several fruit species: Vaccinium corymbosum L. 'Liberty', Prunus persica L. 'Sweet September', Fragaria x ananassa 'Albion', Rubus idaeus L. 'Heritage', Prunus salicina Lindl. 'Angeleno' and Vitis vinifera L. 'Redglobe'. Critical concentration values were determined to avoid phytotoxicity symptoms. Concentrations of ethyl formate gas (0, 1, 2 and 3.5%) were generated from its liquid stage at atmospheric pressure into an 11-litre container. Two exposure times - one hour and two hours were evaluated. The highest concentration of ethyl formate (3.5%) induced slip skin on 'Liberty' blueberries during the 2-h exposure period; sunken areas were observed in 'Sweet September' peaches at 2% during a 1-h exposure period; and 'Albion' strawberry and 'Heritage' red raspberry were very sensitive to the compound. In the former, ethyl formate induced brown discoloration in the sepals and all concentrations resulted in tissue breakdown. In red raspberry, tissue breakdown and bleaching were the main symptoms during a 2-h exposure time even with a 1% concentration of ethyl formate. 'Angeleno' plum and 'Redglobe' table grape did not show visible damage at any of the concentrations. Therefore, the highest, safe concentrations should be: 3.5% for 1 h for blueberries; 1% for 2 h for peaches; and 3.5% for 2 h for plums and table grapes. Further work is needed to verify if the safe concentrations determined here have the necessary effectiveness for use in quarantine insect control.