Gnats off!

For years master gardeners have claimed that putting Bounce brand dryer sheets in their pockets repels pests, but no quantitative data had been obtained to substantiate these claims. However a study from Kansas State University, USA, has been able to provide definitive proof of the effect.¹

Fabric softener dryer sheets are added to dryers to control static cling and give clothes a fresh scent. They contain biodegradable cationic softeners and perfume. To test the sheets’ effectiveness at repelling insects, fungus gnats were released into an experimental area containing sample compartments, some with dryer sheet samples in, some without. This was repeated five times and in all five experiments, the mean proportion of fungus gnat adults collected in the sample compartments containing the dryer sheets were significantly fewer, ranging from 12–18%.

To determine the causes of this effect the team also analysed the volatile compounds in the dryer sheets using GC–MS. One major compound detected was linalool, a colourless monoterpene alcohol used for its flower-like odour. Linalool is present naturally in plants such as lavender, marjoram and basil and has been shown to be toxic to a number of different mites and insects. High levels of the volatile compound beta‑citronellol were also detected. This compound is found in plants including rose geranium, citronella and lemon balm, and is known for its ability to repel mosquitos. The researchers conclude that in the future, the use of dryer sheets may be an alternative strategy to deal with fungus gnat populations in greenhouses.

1. R.A. Cloyd et al., HortScience, 45(12), 1830–1833 (2010).

This story originally appeared in The Column. Click here to view that issue.