No New Age Phenomenon, ‘Natural’ Insecticides Are Rooted in History

What sweet revenge it is on insect pests that well over a thousand plants have insecticidal properties.

So-called “botanical insecticides,” made from ground-up roots, stems, flowers or leaves of such plants, have a long history.

Ancient Greeks and Romans used pulverized roots of white hellebore ( Veratrum album ) to kill insects. Sabadilla, extracted from the seeds of a South American shrub, was used in the 16th Century.

The botanical insecticide you are most likely to find today, nestled on store shelves among garden chemicals, is rotenone.

Toxic to such pests as the Mexican bean beetle, asparagus beetle, aphid, squash bug and cucumber beetle, rotenone degrades rapidly after application, allowing you to eat snap beans a day after you douse them with rotenone. (But wash the beans anyway.)

Although a strong insect poison, rotenone kills slowly, so it would not be the best choice of insecticide to save cucumber plants suddenly descended upon by hordes of cucumber beetles. The plants might be eaten before the insects are dead.

A botanical insecticide that could quickly quell that cucumber beetle attack is pyrethrin. However, insects sometimes recover from a pyrethrin “knockout.” Commercial preparations of rotenone plus pyrethrin combine the benefits of each.

Pyrethrum is made from the dried, ground flower heads of the pyrethrum daisy (Chrysanthemum coccineum, sometimes called the painted daisy), as well as some related daisies.

Pyrethrin was once called Persian or Dalmatian insect powder, and its manufacture in what was then called Persia was a carefully guarded secret that was eventually smuggled out. Pyrethrin is effective against the flea beetle, cucumber beetle, cabbage looper, asparagus beetle, aphid and red spider mite.

Other botanical insecticides include ryania, quassia and sabadilla. Interest in botanical insecticides such as these dropped following the development of DDT, then other synthetic (chemical) insecticides, during World War II.

However, interest in botanicals is on the rise again, and scientists are exploring the insecticidal properties of such things as citrus peel oil, the tropical neem tree and paw paw bark.

Why use a botanical insecticide instead of a synthetic insecticide?

Following exposure to sunlight and air, botanicals degrade rapidly to harmless compounds. Rapid breakdown means that you have to spray frequently, but if you’re picking tomatoes every three days, you do not want a pesticide on them that persists for two weeks.

DDT residues, in contrast, still turn up in odd corners of our planet--the blubber of Arctic mammals, for example. And while insects continually develop resistance to each new synthetic insecticide (the common housefly was able to shrug off the effects of DDT after only two years) resistance to botanical insecticides has not been a problem.

Botanical insecticides are “all natural,” but don’t let that lull you into misusing them.

Botanical insecticides are poisons. Many are toxic to beneficial as well as plant-eating insects. The rotenone you dust on your beans to kill the Mexican bean beetle also will kill beneficial ladybird beetles.

Botanical insecticides are poisonous, in varying degrees, to humans. An insecticide extracted from the tobacco plant is highly toxic, causing headaches, vomiting, and respiratory paralysis from swallowing, inhalation or even skin contact.

Rotenone is moderately toxic to humans, more so than synthetic insecticides such as Sevin and Malathion. Handle botanical insecticides as you would any poison, carefully following directions on the label.

Remember that pest control begins with good gardening practices such as making sure that your plants are well fed and watered, cleaning up plant debris in the fall and growing pest-resistant varieties--not with spraying either a botanical or a chemical poison.