A Tale of Two Pesticides

A Tale of Two Pesticides

August is the prime season for picking up some terrific, locally grown fruits and vegetables. But for many shoppers, there is always that one issue that creates a bit of anxiety: “Should I purchase organic or non-organic produce?”

Any debate about organic gardening is bound to generate a lot of heat, but not much light. Now, organic gardening is more than just a debate about pesticides. It encompasses issues such as composting, recycling and the role of megacorporations. But pesticides are always at the forefront. Perhaps a tale of two pesticides will help clarify where organic and non-organic gardening methods share common ground, and where they do not.

A Choice of Philosophies

There are many conscientious market gardeners, both organic and conventional, who are dedicated to providing safe produce while remaining good stewards of the land. Yet some claim that you can’t be a responsible grower if you use pesticides, and that any pesticide-treated crop presents an unacceptable health risk. The reasoning I hear cited most often to assert the superiority of organic produce is that it’s free of pesticides. But this is not necessarily true—it’s just that the choice of pesticides is different for organic gardeners versus non-organic gardeners.

Rotenone vs. Permethrin

Rotenone is one of the stalwarts of organic gardening. It’s a chemical derived from a variety of plants from the pea family. Rotenone is extracted from the seeds, leaves and roots of these plants, and it controls a wide range of insects.

Permethrin, on the other hand, is a non-organic pesticide, commonly sold under the trade name Ambush. It’s categorized as a synthetic pyrethroid, which means that it’s a chemical similar in structure and effect to pyrethrum, a naturally occurring insecticide found in chrysanthemums. Like Rotenone, Permethrin controls a wide range of insect species.

So what’s the difference between the two when it comes to their effect on the environment?

Both are very safe products, when used properly. But surprisingly, organic Rotenone is more acutely toxic to people than non-organic Permethrin. In fact, if you ate pure Rotenone or pure Permethrin (definitely not recommended!) you would need to eat about four times as much Permethrin as Rotenone to have the same dire effect on your body.

But at the low rates that these two products are applied to edible plants, neither poses any acute toxicity risk, if they are used properly and if the recommended pre-harvest interval (the days between spraying and consumption) is observed. Toxicological data also shows that neither chemical appears to be carcinogenic, even if large amounts of fruits and vegetables treated with these products were consumed every day.

The Lowdown on Breakdown

When it comes to the fate of these two chemicals in the environment, there again appears to be a lot of similarity. Both Rotenone and Permethrin break down in soil rapidly, thanks to the work of microorganisms—Rotenone will break up completely in a few days, while Permethrin might take a few weeks. However, neither chemical moves much in soil, staying in the top few centimetres before they break down, so there’s very low potential for groundwater pollution.
The sun’s ultraviolet light breaks down these chemicals very quickly, which explains why insects can consume the chemically-treated leaves only a day or two after spraying without any ill effects.

Effects on Fauna

Rotenone is very slightly toxic to birds, while Permethrin is practically non-toxic. However, each of these products is toxic to fish, Rotenone particularly so. In fact, Rotenone is often used as a “piscicide” to kill unwanted fish in lakes. On the other hand, Permethrin, although not nearly as toxic to fish as Rotenone, is extremely toxic to bees, while Rotenone is far less so. Of course, you can avoid killing bees by not spraying when they’re pollinating your flowers.

Rational Choices

Choosing the right pesticide isn’t a trivial matter—it’s important to use the correct pesticides only when necessary and only after the pest has been correctly identified. And nobody knows that fact better than the people who provide fresh produce for a living, whether they use organic or conventional means.