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Killer spices provide eco-friendly pesticides

September 29, 2009  By Marg Land

peppermintSeptember 29, 2009 –
Mention rosemary, thyme, clove, and mint and most people think of a delicious
meal. Think bigger – acres bigger.

September 29, 2009 –
Mention rosemary, thyme, clove, and mint and most people think of a delicious
meal. Think bigger – acres bigger.

These well-known spices
are now becoming organic agriculture’s key weapons against insect pests as the
industry tries to satisfy demands for fruits and veggies among the growing
portion of consumers who want food produced in more natural ways.


In a study presented
recently at the American Chemical Society’s 238th National Meeting, scientists
in Canada are reporting new research on these so-called “essential oil
pesticides” or killer spices. These substances represent a relatively new class
of natural insecticides that show promise as an environmentally friendly
alternative to conventional pesticides while also posing less risk to human and
animal health, the researcher says.

“We are exploring the
potential use of natural pesticides based on plant essential oils — commonly
used in foods and beverages as flavourings,” says study presenter Dr. Murray
Isman of the University of British Columbia. These new pesticides are generally
a mixture of tiny amounts of two to four different spices diluted in water.
Some kill insects outright, while others repel them.

Over the past decade, Dr.
Isman and his colleagues tested many plant essential oils and found that they
have a broad range of insecticidal activity against agricultural pests. Some
spiced-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, the researcher says.

“These products expand the
limited arsenal of organic growers to combat pests,” explains Dr. Isman.
“They’re still only a small piece of the insecticide market, but they're
growing and gaining momentum.”

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 — Dr. Isman says. They’re also safer
for farm workers, who are at high risk for pesticide exposure, he notes.

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. Some last only a few
hours, compared to days or even months for conventional pesticides. As these
natural pesticides are generally less potent than conventional pesticides, they
also must be applied in higher concentrations to achieve acceptable levels of
pest control, Dr. Isman says. Researchers are now seeking ways of making the
natural pesticides longer lasting and more potent, he notes.

“They’re not a panacea for
pest control,” cautions Dr. Isman. Conventional pesticides are still the most
effective way to control caterpillars, grasshoppers, beetles and other large
insects on commercial food crops, he says. “But at the end of the day, it comes
down to what's good for the environment and what's good for human health.”

The killer spices aren’t
just limited to agricultural use. Some show promise in the home as eco-friendly
toxins and repellents against mosquitoes, flies, and roaches. Unlike
conventional bug sprays, which have a harsh odor, these natural pesticides tend
to have a pleasant, spicy aroma. Many contain the same oils that are used in
aromatherapy products, including cinnamon and peppermint, Dr. Isman notes.

Manufacturers have already
developed spice-based products that can repel ticks and fleas on dogs and cats
without harming the animals. Researchers are now exploring the use of other
spice-based products for use on fruits and vegetables to destroy microbes, such
as E. coil and Salmonella, which cause food poisoning.

Other scientists are
currently exploring the insect-fighting potential of lavender, basil, bergamot,
patchouli oil, and at least a dozen other oils from exotic plant sources in

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