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Scientists look for ways to increase the production of pyrethrum, a natural pesticide

Researchers at the University of Minnesota recently published a paper on work to generate a new type of pyrethrum produced from the first bloom of Chrysanthemum cinerariifolium.

6/22/2021

Chrysanthemums contain a natural insect repellent called pyrethrum./Credit: Morguefile

Unless you like being bitten by mosquitoes, you've probably used bug spray once or twice in your life. While we use cans full of chemicals, flowers have their own way of preventing pests.

The Sustainable, Secure Food blog, from the American Society of Agronomy (ASA) and Crop Science Society of America, looks at the history and current research surrounding the pyrethrum compound, a natural pesticide.

If you are a gardener, you may have heard of the common trick to plant chrysanthemums around your garden to deter pests. Wonders work too. This is because naturally flowers are high in chemical compounds that insects do not like.

One particular type of chrysanthemum, Chrysanthemum cinerariifolium, is not normally found in nurseries. Its flowers are very rich in the natural compound pyrethrum. It can be used as a natural pesticide in organic farms and as an insect repellent for humans. As such, it has been called a "green pesticide" and researchers are looking for ways to make more of it.

The use of pyrethrum as an insecticide was a well-kept secret by the ancient Persians, for the health of their crops, but its use is documented from around 400 BC. Japan was the main producer of pyrethrum before IIWW, and later African countries began production.

How can you protect it by planting chrysanthemums around your garden? 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 found in its flowers, which are the focus of the harvest. Growers harvest the flowers in specific stages and dry them. Then they grind the flowers and extract the pyrethrum. From there you can make different products, such as powders and liquids.

Current research on pyrethrum

In its natural state, Chrysanthemum cinerariifolium does not flower until its second year of growth. Researchers at the University of Minnesota recently published a paper on working to generate a new type of pyrethrum that can flourish in its first year. This would greatly increase the yield for producers, with an anticipated payoff.

They also looked for varieties that produced more flowers and fewer leaves and stems, which do not contain as much pyrethrum. After their initial research using seeds collected from various sources, they will continue their studies and breeding in hopes of creating a higher-yielding first-year flower grower that produces more natural pyrethrum.

Confusion with names

Ah, if it were that easy to understand the difference in the names of the pyrethrum types. Pyrethrum is the natural compound found in daisies, and Chrysanthemum cinerariifolium is the most highly contained and commercially used type of daisy.

The compound can also be made in the laboratory and in factories (called synthetic). In this case, they are called pyrethrin and are often mixed with other chemicals to enhance their 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 the skin.

Be on the lookout for these different spellings in the name when shopping. As always, read the label directions before using any pesticides or insect repellants.

This research has been published in Crop Science, a journal of the Crop Science Society of America.



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