Pyrethrin comes from the dried flower heads of the pyrethrum daisy, a plant that looks like a plain white daisy in a field. Nothing about it warns you. The pyrethrin plant source is that bloom and little else, since the extract is pulled from the heads rather than the stems or the roots. Mississippi State University Extension calls pyrethrum a botanical insecticide taken from those dried flowers.
The chemistry happens in a spot most people never look at. Hodosan and colleagues place the main biosynthesis in glandular trichomes. Those are tiny surface glands on the disc floret ovaries, the packed yellow parts in the center of the head. That is the reason pickers take the flower and leave the rest of the plant standing in the row. Pyrethrins have also been measured in leaf tissue, but the head carries the load.
Strength swings a lot from plant to plant. Across 25 Croatian populations, the group called chemotype A held the most pyrethrin I, running from 0.36% to 1.30% of dry flower weight. That is a spread of more than three to one inside one species, Chrysanthemum cinerariifolium. A field near the bottom of that range takes far more flowers to yield the same extract. You will see the plant written as Tanacetum cinerariifolium too, and both names point at the same daisy.
Growing regions are few. Kenya is described as the leading exporter of the crop, and Australia grows it in Tasmania. The highlands of Papua New Guinea supply it as well. Beyond that the map thins out fast. No other country gets named in the same breath. The sources name no production shares for any of them, and the crop moves with a harvest rather than a schedule.
The plant is far older than the product. NPIC dates pesticide registration of pyrethrins to the 1950s, and it counts six chemicals in the natural mix found in some chrysanthemum flowers. Some reports put use of pyrethrum at almost 2,000 years, long before anyone could name a single ester in it. The pyrethrin plant source has stayed the same daisy the whole time. It is still one of the most common organic insecticides sold today.
Workers pick the flower heads, since that is where the active compounds sit. Stems and leaves stay in the field.
The heads are dried before anything else happens. Dried flower weight is the basis every strength number is measured against.
The dried material is extracted to pull out the six esters that do the insect killing. What comes off is the crude flower extract.
The extract gets blended into a spray, dust, or concentrate at a stated percentage. That percentage is what belongs on the label.
One label detail trips up plenty of buyers. Pyrethrum names the crude extract taken from the flower. Pyrethrins names the six active esters sitting inside that extract. Both words land on packaging and they read alike, though one points at the plant material and the other points at the chemicals in it.
Read the percentage before you read the name. A bottle marked pyrethrum tells you where the material came from, and a bottle marked with a pyrethrins percentage tells you how much is in there. The second number is the one that changes what happens in your garden. Pyrethrum production still starts with flower heads that get picked and dried. Nothing in the run from field to bottle invents the compound. The daisy makes it, and the processing just concentrates it into something you can pour.
Read the full article: Pyrethrin: What It Kills and How Safe It Is
