Beat Mosquitoes With Sweetgrass

CC BY 2.0. Katja Schulz/Flickr

Researchers reveal what Native North Americans have known forever: Sweetgrass keeps biting bugs at bay.

In this world nothing can be said to be certain, except death, taxes and the nuisance of mosquitoes. They buzz and vex, they keep us up at night and far worse, they were responsible for an estimated 627,000 malaria deaths worldwide in 2012 alone. Man versus mosquito has not been a war won easily, and conventional repellants and pesticides can prove problematic for anyone concerned about exposure to chemicals and potential toxins.

With that in mind, researchers have been looking into repellants that employ components of plants used in traditional therapies. Charles Cantrell, Ph.D., is one such scientist. "We found that in our search for new insect repellents," he says, "folk remedies have provided good leads."

As it turns out, native North Americans have long used fragrant sweetgrass (Hierochloe odorata) to repel biting insects, especially mosquitoes. Now Cantrell and his team report that they have identified the compounds in this meadow grass, native to northern climates, that is the magic ingredient that turns these pesky pests away.


© Andrew Maxwell Phineas Jones, University of Guelph
Cantrell hypothesized that the active insect-repelling chemicals was likely emitted from sweetgrass at ambient temperatures and, like essential oils from lavender and other plants, could be extracted using steam distillation. His team at the U.S. Department of Agriculture along with researchers at the University of Guelph and the University of Mississippi, used steam distillation on samples and evaluated its oil for the ability to deter mosquitoes from biting.

They then tested the sweetgrass oil along with other options including alternative sweetgrass extracts obtained without steam distillation, N,N-diethyl-m-toluamide (DEET) or the ethanol solvent control. Of all the options, the steam-distilled sweetgrass oil tested with the fewest mosquito bites, matching the repellent potency of DEET.

Looking deeper into the specific chemicals that work to fend off the pests, they found three fractions of the oil that repelled mosquitoes as well as the whole. Two chemicals in these active fractions that seemed to be responsible for putting off mosquitoes: phytol and coumarin.

Coumarin is an ingredient in some commercial anti-mosquito products, he adds, while phytol is reported to have repelling activity in the scientific literature. Says Cantrell, "we were able to find constituents that are known to act as insect repellents in a folk remedy, and now we understand that there's a real scientific basis to this folklore."

So to that end, time to plant some sweetgrass? Along with having it in your garden, you can use it traditional-style by making a loop from strands of the grass to be worn around the neck or kept in a satchel hung in homes.