Subject: Pyrethrum/pyrethrin. Was insecticidal soap
From: moholt@gardens.com (Carol Moholt)
Organization: The Bay Area Gardener
Date: Thu, 28 Aug 1997 17:00:10 -0700
Message-ID: <MOD$970828.3916@rec.gardens.ecosystems>
References: <MOD$970822.18666@rec.gardens.ecosystems> <MOD$970822.22664@rec.gardens.ecosystems> <MOD$970826.18701@rec.gardens.ecosystems>


In article <MOD$970826.18701@rec.gardens.ecosystems>, Dan Sterner
wrote:

> I've seen a lot of confusion between the natural and manufactured forms you
> mentioned above, probably because the names are so similar. I have to admit I'm
> not sure of the differences between them myself. Any experts out there that can
> explain it? I'd hate to think I was using something organic and relatively safe
> only to find I'd confused them :)
Tanacetum cinerariifolium is the scientific name for the "pyrethrum
daisy". As far back as the time of the kingdom of Persia, pesticides were
made by grinding up the flower petals from this daisy and applying them in
dust format to other plants to kill unwanted insects.

Many people refer to all products from this plant as "pyrethrums". In
actuality, this term should only be used to the ground up flower petal
products (and few of these products are still available).

A more potent product has been extracted from the seeds of the pyrethrum
daisy. They are called pyrethrins and are what we normally buy when we
purchase a pesticide made from this plant.

Many insects are just stunned, not killed, when sprayed with pyrethrin. To
make sure they die, piperonyl butoxide, a "booster" has been added in most
pyrethrin-based pesticides.

The pyrethrin-based pesticides are labeled with the Caution signal word on
their label. They can cause skin or eye irritation. They do kill fish. As
a pesticide, they are most effective against soft-bodied insects. They
kill upon contact, so if the insect can escape the the spray, it will
live. Some populations have become resistent to pyrethrins. Others are
only susceptible in a certain phase. For example, pyrethrin won't kill the
hard-shelled egg or nymph phase of the whitefly, although it may kill the
flying adults.

Some people widely spray their garden with pyrethrins, thinking that "it
is organic, and safe, and so is a good thing". What you have to remember
is that it may also kill beneficial insects that you want to preserve.
While many people are very careful about not spraying a "strong, chemical
pesticide" anywhere in their garden, they may become very nonchalant about
pyrethrin use. I have seen many gardeners ignore the precautionary
statements on products containing pyrethrins. They don't mix them
carefully, they don't keep them off their skin, or, casually pour unused
product down the drain to run into the local water source. They also spray
it on their entire garden at regular intervals.

I think it is very important to be careful in using any pesticide, whether
it come from a flower or the chemist's test tube. It bothers me greatly to
see the marketing phrases on products containing pyrethrins. They contain
slogans like "made with botanical pyrethrins from Chrysantheumum flowers"
and lull many gardeners into a very cavalier usage.

Carol Moholt