The organic arsenal does include a number of pesticides, but organic gardeners, knowing that “natural” is not the same thing as “harmless”, use these only as helpers of last resort. Although they are comparatively benign, all can hurt non-target organisms like bird, fish, and beneficial insects. Some, including ryania, are very strong poisons to mammals as well; while if rotenone gets into your system, it may help trigger the development of Parkinson’s disease.
Always wear protective clothing when applying pesticides. Read the label carefully to be sure the pesticide you’re using is approved for the pest (and the plant) on which you intend to use it. Follow dosage directions; this is definitely one place where more is not better.
Neem, from the neem tree, Azadirachta indica. Multiple actions: repels pests, destroys their appetites, kills them by disrupting their growth. Also has some fungicidal properties. Useful against a wide range of pests including flea beetles, whiteflies, corn earworms, cabbage loopers, and root-knot nematodes.
Pyrethrum, from flowers of Chrysanthemum cinerariifolium and C. coccineum. Instant knockdown, which is very gratifying. But it doesn’t always last; if the dosage is improper or the insect has resistance, the victim gets up and staggers away as soon as you turn your back. If you use the proper amount, however, and manage to get it to land on the target, pyrethrum is useful against almost any invertebrate that may be plaguing you. (Be very careful about using pyrethrum or ins derivatives on cats; small amounts rid them of fleas, but if you overdo it, you will also be rid of Fluffy)
Rotenone, from several species of legumes in the genus Lonchocarpus. Use it and watch the beetles die. Mexican bean beetles, potato beetles, cucumber beetles — even the adults of these hard-to-kill scourges are not immune. Neither, unfortunately, are fish, birds, small mammals, or much of anything else. Rotenone degrades rapidly, but it’s very strong stuff while it lasts.
Ryania, from a shrub called Ryania speciosa, and like rotenone, short lived but no joke. Use on the caterpillars of codling moths and cabbageworms, and the larvae of Japanese beetles, bean beetles, and potato bugs.
Sabadilla, from the South American plant Schoenocaulon officinale. Use only when all else fails, on things like thrips, squash bugs, and tarnished plant bugs. Sabadilla is extremely toxic to bees; be sure to apply it only after they have gone home for the night.
Peperonyl butoxide (PBO) may or may not be plant derived; it can come from sesame oil but is also chemically synthesized. It is an insecticide in its own right, but it is most commonly used as a synergist, combined with other pesticides (especially pyrethrum). It destroys an insect’s ability to fight off the pesticide, making the product more effective, and at lower doses, than it would otherwise be. But PBO is not on everyone’s organic-acceptable list, and may cause health problems, so you may prefer to avoid it.