Sulfur Dioxide Killed Thrips in USDA Tests, but Produce Quality Set the Limit

A USDA study found that brief sulfur dioxide fumigation eliminated western flower thrips in controlled tests at cold storage temperature. The same trials also showed why a treatment that works against an insect cannot automatically be used across every fresh produce category: broccoli was visibly damaged, while peppers and navel oranges retained their appearance.

The peer reviewed work by Agricultural Research Service scientist Yong Biao Liu was published in Agriculture in February 2024. USDA has since highlighted it in a research explainer on alternatives for postharvest pest control. This is a research result, not an announcement that a new commercial treatment is approved for general use.

What the experiment measured

Western flower thrips are a quarantine concern for some export markets and can transmit plant viruses. The researchers exposed the insects to sulfur dioxide at 5°C. A 30 minute treatment at 0.5% concentration and a 60 minute treatment at 0.3% each produced complete mortality in the tested insects.

The team then tested short fumigation treatments with thrips on broccoli, bell peppers, apples and navel oranges. Pest control held across the tested products, but the produce responded differently. Bell peppers and navel oranges showed no observed negative effect on visual appearance. Broccoli developed severe discoloration, while green apples showed darkened lenticels, the small pores visible on the skin.

The commercial question is product fit

For an exporter, pest mortality is only one hurdle. A postharvest treatment also has to preserve saleable quality and meet the rules of both the origin and destination markets. The contrast among the four commodities is therefore the practical finding: a validated protocol for citrus or peppers cannot simply be transferred to broccoli or apples.

The paper tests a particular insect, concentrations, treatment times, temperature and product set. It does not establish performance against every life stage or pest, nor does it by itself settle residue limits, worker safety, permitted uses, scaled handling or approval in an importing market. Operators would need a formally validated and authorized protocol before treating commercial shipments.

Sulfur dioxide is a controlled fumigant, not a home or farm remedy. USDA’s results point to a possible additional postharvest tool for selected produce, while making the case for commodity specific quality testing before any broader use.