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Pyrethroid, pyrethrum, pyrethrins — an explanation

Natural pyrethrum has been around for hundreds of years and it is such a great insecticide, organic chemists of the 60s and 70s began to tease apart the molecules and synthesize them using various alcohols and esters. Now there are hundreds of these derivatives and as a group, they are called pyrethroids — or synthetic pyrethroids.

The variations are many; some are more light-stable and therefore more residual than others which may have a quicker knockdown, and there are variations in the effects on the pest organism to give the manufacturer an edge for a particular problem.

So what are “pyrethrins”? They are insecticidal bits of natural pyrethrum; the isomers that provide the real result. The other parts of natural pyrethrum (jasmolins and cinerins) are much less insecticidal so only the real actives are listed on the label as “pyrethrins.”

There is a swing back to natural pyrethrum particularly by growers wanting to avoid insecticide resistance problems. There is no resistance to the natural product and it can easily kill resistant whiteflies and resistant Western flower thrips, the two main pests with a resistance reputation. Growers looking to add another insecticide to their list are choosing to try it.

Because it kills the pests by contact and within 15-20 minutes, growers can assess the results on a small patch of infested crop before going ahead and spraying the whole area. The withholding period is just 1 day and the re-entry time is one second after the last droplet has settled.

To some, the word “natural” means “doesn’t really work.” Natural it may be but it kills pests within minutes, including beneficials. A factor to consider is the very short residual life — a couple of hours in sunlight — so it is possible to rescue a disastrous situation and reintroduce beneficials within days (once they have some new pests to eat) if that is your intention.


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