Herbs act as eco-friendly pesticides

These substances represent a relatively new class of natural insecticides that show promise as an eco-friendly alternative to synthetic chemical pesticides.

"We are exploring the potential use of natural pesticides based on plant essential oils -- commonly used in foods and beverages as flavourings," said study presenter Murray Isman of the University of British Columbia (UBC).

These new pesticides are generally a mixture of tiny amounts of two to four different herbs diluted in water. Some kill insects outright, while others repel them.

Over the past decade, Isman and colleagues tested many plant essential oils and found that they have a broad range of insecticidal activity against pests.

Some herb-based commercial products now being used by farmers have already shown success in protecting organic strawberry, spinach, and tomato crops against destructive aphids and mites.

"These products expand the limited arsenal of organic growers to combat pests. They're still only a small piece of the insecticide market, but they're growing and gaining momentum," he said.

The natural pesticides have several advantages. Unlike conventional pesticides, these "killer spices" do not require extensive regulatory approval and are readily available.

An additional advantage is that insects are less likely to evolve resistance -- the ability to shrug off once-effective toxins. They're also safer for farm workers, who are at high risk for pesticide exposure, he noted.

But the new pesticides also have shortcomings. Since essential oils tend to evaporate quickly and degrade rapidly in sunlight, farmers need to apply the spice-based pesticides to crops more frequently than conventional pesticides.

Researchers are now seeking ways of making the natural pesticides longer-lasting and more potent, he noted.

These findings were presented at the American Chemical Society's 238th National Meeting.