Investigating the potential of ethyl formate fumigation for phytosanitary control of the grain chinch bug on pome and stone fruit

Due to the lack of postharvest mitigation treatments for the grain chinch bug, a cold hardy external phytosanitary pest of South African export fruit, and the need for alternatives to methyl bromide fumigation, the efficacy of ethyl formate fumigation against grain chinch bug was assessed. Ethyl formate (EF) is considered to be the most promising fumigant to replace methyl bromide.

Efficacy trials. To investigate the effect of fumigation with ethyl formate on the mortality of grain chinch bug, as well as the effect of fumigation on fruit quality, selected plum, nectarine and pear cultivars (‘Songold’ plums, ‘August Red’ nectarines, ‘Russet Gold Bosc’ and ‘Forelle’ pears) were treated together with live adult grain chinch bugs. Three concentrations of EF were applied (50, 100 and 150 g/m³) t to examine its effectiveness after 1 h of fumigation to control grain chinch bug.

Central composite design model trial. To determine optimum dose, duration and treatment temperature to achieve 100% mortality of the grain chinch bug with no phytotoxic effect on ‘Russet Gold Bosc’ pears, a central composite design (CCD) model was used. A CCD model was compiled for three different pulp temperatures (0, 10 and 23°C) to determine if the product’s temperature at time of treatment play a role in its susceptibility to damage.

Ethyl formate achieved a 100% mortality of grain chinch bug with the dose range of 50 – 150 g/m³ after 1-hour exposure without decreasing fruit quality significantly.

The CCD model was able to provide guidelines with regards to dose range and duration which yielded no phytotoxic effect after cold storage plus shelf-life simulation.

Ethyl formate was successful in controlling grain chinch bug without phytotoxic effect. This knowledge needs to be expanded to enable commercial application of ethyl formate/ Vapormate^TM for external pests. The development of successful treatments will not only help maintain current markets which are constrained by available mitigation options, but will also allow for market expansion and growth of the industry.