- published: 13 Aug 2015
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Pyrethrum refers to several Old World plants of the genus Chrysanthemum (e.g., C. coccineum) which are cultivated as ornamentals for their showy flower heads. Pyrethrum is also the name of a natural insecticide made from the dried flower heads of Chrysanthemum cinerariifolium and Chrysanthemum coccineum.
Some members of the Chrysanthemum genus, such as the following two, are placed in the Tanacetum genus instead by some botanists. Both genera are members of the daisy (or aster) family, Asteraceae. They are all perennial plants with a daisy-like appearance and white petals.
Pyrethrum was used for centuries as an insecticide, and as a lice remedy in the Middle East (Persian powder, also known as "Persian pellitory"). It was sold worldwide under the brand Zacherlin by Austrian industrialist J. Zacherl.
The flowers should be dried and then crushed and mixed with water. It should be noted that though the pesticide is natural, it can still be harmful to humans.
Because of the natural insecticidal properties of the pyrethrums, they are used as companion plants, to repel pest insects from nearby crops and ornamental plants. They are thought to repel aphids, bed bugs (Cimex lectularius), leafhoppers, spider mites, harlequin bugs, ticks, pickleworms and imported cabbage worms, among others that are in gardens and farms. For example, they are planted among broccoli plants for protection from several common insect pests.