August 18, 2009

Common herbs and spices show promise as an environmentally-friendly alternative to conventional pesticides in crop production, Canadian scientists from the University of British Columbia revealed in a major US conference.

 

The scientists have spent 10 years researching on the insecticidal properties of rosemary, thyme, clove and mint, and found they could become a key weapon against insect pests in organic agriculture.

 

The "plant essential oils" have a broad range of action against bugs, with some killing them outright while others repel them.

 

The new pesticides are generally a mixture of tiny amounts of two to four different herbs diluted in water.

 

Some spice-based commercial products now being used by farmers have already shown success in protecting organic crops against destructive aphids and mites, said Dr Murray Isman, who led the research.

 

These products, which have a small but growing market, expand the limited arsenal of organic growers to combat pests, he said.

 

Unlike conventional pesticides, these pesticides do not require more limited approval from regulatory bodies and are readily available. Insects are also less likely to evolve resistance, and the products are safer for farm workers who are at high risk for pesticide exposure, Dr Isman said.

 

But the herb-based pesticides also have shortcomings.

 

The essential oils made from the herbs tend to evaporate quickly and degrade rapidly in sunlight, therefore they need to be applied to crops more frequently than conventional pesticides required.

 

Some last only a few hours, compared to days or even months for conventional pesticides.

 

Herb-based pesticides are also less potent than conventional ones, so they must be applied in higher concentrations to achieve acceptable levels of pest control, Dr Isman said.

 

Researchers are now seeking ways to make the herb-based pesticides last longer and more potent, he said.

 

Meanwhile, conventional pesticides are still the most effective way of pest control, he conceded.