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Pyrethrum Insecticide

- Natural pyrethrum versus synthetic permethrin -

Summary: There is a lot of confusion over the insecticide names permethrin and pyrethrum. Permethrin is a man-made insecticide whose chemistry is based on natural pyrethrum. This article examines the important differences between these similar-sounding pesticides.

Jack DeAngelis, PhD
OSU Ext. Entomologist (ret.)
my resume

Pyrethrum, or "insect powder", insecticide

Pyrethrum ("pie-wreath-rum") is a natural insecticide made from certain species of the chrysanthemum. It is a mixture of several different compounds called pyrethrins and cinerins. Originally pyrethrum was made by grinding dried chrysanthemum flowers into a powder. Today, pyrethrum is extracted with solvents but is still widely used in household insect sprays where it is usually combined with another chemical called piperonyl butoxide (PBO).

About 200 years ago people in central Asia discovered that dried, crushed flowers of certain chrysanthemums were toxic to insects. During the Napoleonic Wars (1804-1815) this "insect powder" was used to control flea and body lice infestations by French soldiers. Since then, pyrethrum has been used in many forms for effective, low toxicity insect control. However, because natural pyrethrum is not stable in sunlight it is seldom used in commercial agriculture.
source of pyrethrum - chrysanthemum flowers

Certain types of chrysanthemum flowers are the source of natural pyrethrum. Original photo by USDA.

Using natural pyrethrum in home gardens

Pyrethrum insecticide, either alone or in combination with other compounds, is a very effective, safe and environmentally friendly garden insecticide. They are very effective against a wide array of garden pests and can often be used right up to the day of harvest (see label instructions).

Pyrethrum is one of the botanical insecticides and is often combined with neem oil or insecticidal soap to make a highly effective, wide spectrum, low toxicity spray. These combination products can be used for aphids, scale insects, spider mites, thrips and many other leaf-feeding garden pests. Pyrethrum-based garden insecticides and other least-toxic garden pesticides are available at our 'Bugs Store.

Permethrin insecticide

Permethrin ("per-meth-rin"), on the other hand, is a synthetic, man-made insecticide, whose chemical structure is based on natural pyrethrum. The so-called pyrethroid insecticides were developed to match or exceed the effectiveness of natural pyrethrum but be more stable in sunlight. Pyrethroid insecticides are used in agriculture because of their stability in sunlight.

Permethrin is widely used and has recently enjoyed an upswing in homeowner popularity since the widely used insecticide diazinon was taken off the US market. Permethrin has many uses from landscape pest control to head lice shampoos, flea, tick and mosquito control on dogs, and mosquito control on outdoor clothing and camping gear. Permethrin is relatively low toxicity but highly toxic to cats and some other animals.

Is natural pyrethrum a pyrethroid?

No. Pyrethrum is a relatively low toxicity natural insecticide and since it breaks down quickly, generally has low environmental impact as well. For these reasons it enjoys a reputation of being "safe". Pyrethroid insecticides, on the other hand, are generally more toxic, more environmentally persistent and therefore not as "safe". Unfortunately, some marketers continue to claim that pyrethroid insecticides like permethrin are "made from chrysanthmum flowers" implying that they are "natural and safe". These claims are false, and if done intentionally to mislead the claims are highly unethical.

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Mission: To provide accurate, up-to-date and unbiased information for solving common insect and mite problems around your home, business and landscape using least-toxic methods.

Jack DeAngelis, PhD,  , email:  [email protected]

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