Toronto, Aug 17 - Well-known herbs rosemary, thyme, clove and mint are now becoming killer weapons against pests as the industry tries to satisfy demands for fruits and vegetables produced in more natural ways.

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.