Pyrethrum rapidly paralyzes pests. Because the pyrethrum mammalian toxicity is very low, it can be applied to food crops close to harvest. Some individuals with ragweed pollen allergies have suffered allergy attacks after exposure to pyrethrum dust. Pyrethrum has a high contact toxicity for common beneficials, such as Encarsia formosa , predaceous mites and Aphidlete aphidimyza . Rotenone, made from the roots of tropical plants, is probably the most widely-available botanical insecticide.
Rotenone lasts a week or less after application because it is rapidly degraded by sunlight.
Rotenone has the lowest DL 50 value of the commonly-used botanicals, making it the most toxic. Like most synthetic pesticides, Rotenone acts on the nervous system. Small doses may be irritating to mucous membranes. This product is highly toxic to fish and other aquatic life. It has been commonly used as a fish poison.