Chrysanthemums, commonly known as mums, are popular ornamental garden plants. They also have a long history connected to natural pest management. The belief that these flowers possess innate insect-repelling properties stems from the presence of powerful chemical compounds within the plant itself.
The Repellent Compound Pyrethrin
The insecticidal activity of certain chrysanthemum species is attributed to pyrethrins, a family of naturally occurring pesticides found within the flowers. Pyrethrins are a mixture of six related chemicals, concentrated primarily in the seed cases of the flower head. These organic compounds are extracted commercially from the species Chrysanthemum cinerariifolium, often called the Dalmatian daisy.
Pyrethrins function as potent neurotoxins that target the nervous systems of insects upon contact or ingestion. The compounds bind to and delay the closure of voltage-gated sodium channels in the nerve cells. This action causes sodium ions to flood the nerve cell, leading to persistent depolarization of the nerve membrane.
The result is hyperexcitation of the insect’s nervous system, causing continuous, uncontrolled firing of electrical signals. This hyperactivity manifests as tremors, convulsions, and a rapid loss of motor coordination, often termed the “knockdown” effect. Pyrethrins often require a secondary compound, known as a synergist, in commercial products to prevent the insect from detoxifying the chemical before death.
Specific Insects Controlled by Chrysanthemums
Pyrethrins are broad-spectrum insecticides used to control a wide range of pest species. They are effective against common garden pests that feed on plant sap or foliage:
- Aphids
- Thrips
- Spider mites
- Leafhoppers
- Whiteflies
Pyrethrin-based products are also used to control household and health pests. They target flying insects such as mosquitoes, flies, and moths, as well as crawling pests including fleas, ticks, ants, and cockroaches.
In lower concentrations, pyrethrins exhibit a repellent effect, particularly against biting insects like mosquitoes. This dual action of paralyzing at high doses and repelling at low doses makes pyrethrin an important tool in public health pest control.
Practical Methods for Using Chrysanthemums
Simply planting chrysanthemums in the garden offers only minimal pest protection. The concentration of pyrethrins in the leaves and petals of a live plant is generally not sufficient to act as a standalone pesticide. Some varieties may slightly deter insects with their scent, but they do not provide the killing power of processed extracts.
The potent properties are utilized when the flowers are dried and processed into concentrated products. This concentrated form, known as pyrethrum powder, can be used as a dust or refined into a liquid spray. Commercial products allow for targeted application and much higher concentrations of the active ingredient. Because pyrethrins break down rapidly when exposed to sunlight, they are considered a less persistent alternative compared to many synthetic pesticides.