Organic Gardening and Pesticides

We've been talking about organic gardening over the past few weeks, both in email and face to face.

It sounds like most folks are in favor of restricting the garden to organic methods of pest control.

Here's a short list of organic pesticides and a little information on each.

insecticidal soap
Insecticial soap is soap, with basically all the safety concerns (i.e. very few) of soap. Insecticidal soap does not have any lasting insecticidal activity, especially if washed off as recommended by the linked site.

neem oil
Neem oil is an extract from a tree (the seed) indigenous to southern India. Neem oil has been used as an insecticide and ingested for hundreds of years. (I do not advocate eating your bottle of neem-based pesticide, no matter how enticing the packaging.) Neem oil also has anti-microbial and anti-fungal properties and can be found in many cosmetics.

Neem oil's insecticidal properties are fairly broad spectrum and also targets mites. Unlike many chemical pesticides, neem oil does not usually kill on contact. Instead, neem oil discourages feeding in the affected insects.

Neem oil does not seem to affect beneficial insects, including bees and ants, nor does it appear to affect earthworms detrimentally.

horticultural oil
Horticultural oil is a petroleum-based oil that coats insect pests, preventing them from feeding and breathing, similar to mineral oil.

baking soda (sodium bicarbonate) or potassium bicarbonate mixed with oil
Potassium bicarbonate mixed with oil and sprayed on leaves can serve as a fungicide.

capsaicin spray
Capsaicin is the heat-inducing component in chili peppers. As such, it's quite safe. Capsaicin sprays may repel small mammals, such as squirrels or rabbits. A friend of mine coats his pumpkins with the stuff to ward the squirrels off every year.

Bt dust (sometimes liquid)
Bt is a bacterium that disrupts insects' ability to digest food. Different varieties of Bt affect different insects, and Bt appears to have no toxicity in humans.

pyrethrins
Pyrethin based pesticides are derived from chrysanthemum flowers and have low toxicity in mammals. As such, they are extremely safe. However, they can kill beneficial insects quite effectively.

rotenone
Rotenone is a pesticide commonly used in organic gardening because it breaks down quickly when exposed to sunlight. Many formulations are of fairly low toxicity to mammals, but some are not. Rotenone is extremely toxic to fish and also kills beneficial insects indiscriminately.

sevin dust
Another pesticide that breaks down rapidly, sevin dust also can target beneficial insects.

This list is missing some (milky spore, diatomaceous earth, etc.) but this is a good start.

I would question using rotenone, sevin dust, or pyrethrin powder as they can kill beneficial insects.