Pyrethrins are contact poisons which quickly penetrate the nerve system of the insect. A few minutes after application, the
insect cannot move or fly away. But, a "knockdown dose" does not mean a killing dose. The natural pyrethrins are swiftly detoxified
by enzymes in the insect. Thus, some pests will recover. To delay the enzyme action so a lethal dose is assured, organophosphates,
carbamates, or synergists may be added to the pyrethrins.
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. Today Kenya and Tasmania are the largest pyrethrum growing and producing countries.
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 extract the insecticide pyrethrum.
Pyrethrum is an ancient insecticide. The insecticide properties of the flowers were documented in the early 1800ís
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 high grade product.
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 agricultural pests.