What is pyrethrum?

By Chelsie Vandaveer

November 13, 2002

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A daisy or mum 'flower' is actually an inflorescence made up of two types of flowers, ray flowers which appear as petals and are usually sterile, and disk flowers which tightly cover the center each producing a single seed. These inflorescences are typical of the Asteraceae [as ter a' see ee]. Two species within this family, the Dalmatian insect flower (Tanacetum cinerariifolium ((Trevir.) Vis.) Schultz-Bip.) and the Persian or painted daisy (T. coccineum (Willd.) Grierson), are the primary sources of pyrethrum.

Pyola® Insect Spray – Canola oil with pyrethrins-an insecticide from plants for plants

Signature Product Pyola is a broad-spectrum spray that combines pyrethrin, a long-popular insecticide derived from chrysanthemum flowers, with canola oil extracted from rapeseed. Unlike most pesticides, it controls all stages of a pest insect's life cycle, including eggs. Click here - $20 FREE off your first order at Gardens Alive! [ More Insect Pest Control! ]

Pyrethrum is an insecticide made from the whole inflorescences of these plants. The 'flowers' are picked, dried, and powdered. Natural pyrethrum contains six active chemicals—pyrethrins I and II, cinerins I and II, and jasmolins I and II. Generally referred to as pyrethrins, these chemicals are concentrated within the flowers. Little is found elsewhere in the plants, but enough that insects leave the pyrethrum-producing plants alone.

Pyrethrins* are contact poisons which quickly act upon the nervous system. In small doses, insects are knocked down; the toxins excite the neurons causing convulsions. In the final stages of poisoning, the insect cannot coordinate its voluntary muscles (ataxia); the nervous system appears 'exhausted'. But insects can recover unless the dosage is sufficient to kill. (Pyrethroids, Department of Entomology, Purdue University, 2002)

For pyrethrum to be fully lethal to insects, it is generally combined with a 'synergist', a chemical that enhances the pyrethrins action on the nervous system. The synergist may be as simple as vegetable oil or diatomaceous earth, or more complex like piperonyl butoxide.

Pyrethrins have low toxicity to mammals, because mammals can metabolize the chemicals. But poisoning can occur or worse, a severe allergic reaction—asthma or anaphylaxis.

Pyrethrum is unstable; the pyrethrins breakdown in the presence of sunlight, moisture, or oxygen making the chemicals biodegradable. In the past two centuries of pyrethrum use, very few insects have developed resistance to these toxins.

Pyrethrum production is an interesting process. The Pyrethrum Board of Kenya has an excellent informational website about pyrethrum. To view the website, click on the link:

http://www.kenya-pyrethrum.com

*Pyrethrins are the chemicals made by plants in the Asteraceae. Pyrethroids are semi-synthetic or synthetic chemicals designed to mimic pyrethrins, but have longer residual action. To learn more about pyrethroids, Cooperative Extension Offices of Cornell University has an excellent article about these pesticides:

http://extoxnet.orst.edu/pips/pyrethri.htm

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