By Margaret Geick, Colorado Master Gardener SM , Colorado State University Cooperative Extension, Denver Insecticides and other pesticides sometimes are needed as a last resort when efforts to grow a healthy plant fail and pests strike. Rotenone, nicotine, pyrethrum and neem are examples of botanical insecticides. Just because the materials are natural, however, doesn't mean they are always less toxic than the synthetics.
Rotenone is produced from the roots of two tropical members of the bean plant family.
It has been used as a crop insecticide since the mid-1800's to control leaf eating caterpillars, and it often is recommended for flea beetle control on early season vegetables. Nicotine sulfate has been used since the turn of the century and is the most hazardous botanical insecticide available to home gardeners. The insecticide is extracted from tobacco by steam distillation or solvent extraction. Highly toxic to humans and other warm blooded animals, nicotine sulfate is rapidly absorbed through the skin. It is six times more toxic than diazinon, a widely available synthetic insecticide sold for control of many of the same pests.