Gardening Pesticides

Where does pyrethrum come from?

Scientists are looking at ways to make more
of this natural pesticide

By Susan Fisk

If you’re a gardener, you may have heard of the common trick of planting chrysanthemums around your garden to deter pests. Or marigolds. This is because the flowers naturally are high in chemical compounds that insects don’t like.

One particular type of chrysanthemum, Dalmatian chrysanthemum – Chrysanthemum cinerariifolium (Tanacetum cinerariifolium according to some sources) – isn’t typically found in nurseries. Its flowers are very high in the natural compound pyrethrum. It can be used as both a natural pesticide on organic farms and as an insect repellent for humans. As such it’s been called a “green pesticide” and researchers are looking at ways to make more of it.

The use of pyrethrum as an insecticide for the health of crops was a secret well kept by ancient Persians, but its use is documented from around 400 B.C. Japan was the leading producer of pyrethrum before World War II, and later African countries began production.

Clary sage showing trichomes.
Some plants have glands that secrete chemical compounds through trichomes. Shown: clary sage secreting sclareol through its trichomes. Photo: SV Fisk

How can planting chrysanthemums around your garden protect it? Plants have glands, called trichomes. And some plants secrete a chemical compound from these glands, in this case, pyrethrum. It doesn’t have the best smell.

In the case of Chrysanthemum cinerariifolium, the highest concentration of pyrethrum is in its flowers, which are the focus of the harvest. Growers harvest the flowers at specific stages and dry them. They then grind the flowers and extract the pyrethrum. From there, different products can be made, like powders and liquids.

Dog and cat cuddled together.
Pyrethrum, a natural chemical found in chrysanthemums, can repel insects like mosquitoes and ticks. Pyrethrum can be used in dog shampoos but not cat shampoos as it’s toxic to cats, and has to be dosed just right for dogs. Photo: C. Flores

Current Research About Pyrethrum

In its natural state, Chrysanthemum cinerariifolium doesn’t flower until its second year of growth. Researchers at the University of Minnesota recently published a paper about the work to breed a new type of pyrethrum that can flower in its first year. This would greatly increase the yield to growers, with an early payoff.

They were also looking for varieties that grew more flowers and fewer leaves and stalks, as they don’t contain as much pyrethrum. After their initial research using seeds collected from various sources, they will continue their studies and breeding in hopes to create a higher-yielding, first-year flower producer that makes more natural pyrethrum.

Confusion With Names

A Dalmation chrysanthemum farmer in her field in Tanzania. Credit: Pyrethrum Company of Tanzania

Ah, if only it were easy to understand the difference in names of types of pyrethrum! Pyrethrum is the natural compound found in chrysanthemums, and Chrysanthemum cinerariifolium is the type of chrysanthemum that contains the most and is used commercially.

The compound can also be made in the lab and factories (it is then said to be synthetic). In this case, it is referred to as pyrethrin (not pyrethrum) or said to be a pyrethroid and is often mixed with other chemicals to enhance its effects. 

Permethrin is another synthetic compound based on the chemical structure of natural pyrethrum. It is used to treat clothing, tents, and outdoor equipment, not skin.

Watch for these different spellings in the name when you go to make a purchase. 

As always, read label directions before using any pesticide or bug spray.

Compiled by Susan Fisk, from research published in Crop Science, a journal of the Crop Science Society of America.

This article was written by a member of the American Society of Agronomy and Crop Science Society of America. Their  members are researchers and trained, certified, professionals in the areas of growing our world’s food supply while protecting the environment. They work at universities, government research facilities, and private businesses across the United States and the world.

Larry Hodgson is one of Canada’s best-known garden communicators. He has notably been editor-in-chief of HousePlant Magazine, Fleurs, Plantes et Jardins, À Fleur de Pot and Houseplant Forum magazines and is currently the garden correspondent for Le Soleil and radio garden commentator for CKIA-FM Radio. He has written for many garden publications in both the United States and Canada, including Canadian Gardening, Harrowsmith, Horticulture, Fine Gardening and Organic Gardening. He also speaks frequently to horticultural groups throughout Canada and the U.S. His book credits include The Garden Lover’s Guide to Canada, Complete Guide to Houseplants, Making the Most of Shade, Perennials for Every Purpose, Annuals for Every Purpose, and Houseplants for Dummies, as well as nearly 60 other titles in English and French. He is a past president of the Garden Writers Association (now Garden Communicators International) and the winner of the prestigious 2006 Garden Media Promoter Award offered by the Perennial Plant Association. He resides in Quebec City, Quebec, Canada.

2 comments on “Where does pyrethrum come from?

  1. I believe all the synthetic versions, in which there are molecular differences between these and the natural pyrethrum, are called pyrethroids. But I’m not an expert.

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