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Organic pesticides not always ‘greener’ choice, U of Guelph study finds


July 6, 2010
By Dave Harrison


Topics

July 6, 2010 – Consumers shouldn't assume that because a
product is organic it's also environmentally friendly.

July 6, 2010 – Consumers shouldn't assume that because a
product is organic it's also environmentally friendly.

A new University of Guelph study reveals some organic
pesticides can have a higher environmental impact than conventional pesticides
because the organic product may require larger doses.

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This research was featured in last month in the Globe and Mail and on
the CBC website.

Environmental sciences professor Rebecca Hallett and PhD
candidate Christine Bahlai compared the effectiveness and environmental impact
of organic pesticides with those of conventional and novel reduced-risk
synthetic products on soybean crops.

“The consumer demand for organic products is increasing
partly because of a concern for the environment,” said Hallett. “But it’s too
simplistic to say that because it’s organic it’s better for the environment.
Organic growers are permitted to use pesticides that are of natural origin, and
in some cases, these organic pesticides can have higher environmental impacts
than synthetic pesticides, often because they have to be used in large doses.”

The study, which was published last month in the journal PloS
One
, involved testing six pesticides and comparing their environmental impact
and effectiveness in killing soybean aphids — the main pest of soybean crops
across North America.

The scientists examined four synthetic pesticides: two
conventional products commonly used by soybean farmers and two new reduced-risk
pesticides. They also examined a mineral oil-based organic pesticide that
smothers aphids and another product containing a fungus that infects and kills
insects.

The two researchers used the environmental impact quotient,
a database indicating impact of active ingredients based on such factors as
leaching rate into soil, runoff, toxicity from skin exposure, consumer risk,
toxicity to birds and fish, and duration of the chemical in the soil and on the
plant.

They also conducted field tests on how well each pesticide
targeted aphids while leaving their predators — ladybugs and flower bugs —
unharmed.

“We found the mineral oil organic pesticide had the most
impact on the environment because it works by smothering the aphids and
therefore requires large amounts to be applied to the plants,” said Hallett.

Compared with the synthetic pesticides, the mineral
oil-based and fungal products were less effective because they also killed
ladybugs and flower bugs, which are important regulators of aphid population
and growth.

These predator insects reduce environmental impact because
they naturally protect the crop, reducing the amount of pesticides that are
needed, she added.

“Ultimately,
the organic products were much less effective than the novel and conventional
pesticides at killing the aphids, and they have a potentially higher
environmental impact. In terms of making pest-management decisions and trying
to do what is best for the environment, it’s important to look at every
compound and make a selection based on the environmental impact quotient rather
than if it’s simply natural or synthetic. It’s a simplification that just
doesn’t work when it comes to minimizing environmental impact.”


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