“…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.” Rebecca Hallet, PhD Candidate, University of Guelph

Excerpt:

[A] study, which is published 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 two 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.

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

http://www.sciencedaily.com/releases/2010/06/100622175510.htm