Pyrethrum is a botanical insecticide produced primarily in the flowers of Tanacetum cinerariaefolium, a species of the chrysanthemum plant family. Pyrethrum plants have historically been grown in commercial quantities in Kenya, Tanzania, Rwanda and Papua New Guinea. Over the past decade, Tasmania and Uganda began producing pyrethrum.
In East Africa the mature pyrethrum flowers are picked by hand, sun dried to remove moisture, and sent to a processing plant for extraction of the active ingredient-pyrethrins, a mixture of six closely related esters. In Tasmania the flowers have been bred to synchronously flower so they can be mechanically harvested. As in Africa, the flowers are sun dried and processed to produce the insecticide pyrethrum.
The insecticide properties of Pyrethrum were documented in the early 1800’s but it is suspected that the flowers were used to kill insects a considerable time earlier. The first commercially available products were powders made from ground flowers and later crude oil extractions became popular. Today, the refining of crude pyrethrum extract to remove the plant material, waxes, etc. is a highly complex process resulting in a very pure product from which most other plant properties have been removed.
Pyrethrum has been used effectively to control insects for decades and is non-persistent, decomposing rapidly in the environment. This rapid degradation of pyrethrum has resulted in little known cases of insect resistance making it an excellent choice for the control of insects in a wide variety of settings.
From a toxicological viewpoint, pyrethrum has been extensively studied. It is low in acute toxicity to man and other vertebrate animals. It recently went through a thorough review by the US EPA during the re-registration process. Similarly pyrethrum has been listed on Annex I on the plant protection directive in the EU (#91/414) and is under review in the Biocides Directive (98/8).