Pyrethrum daisies are simple and pretty flowers that are often grown as ornamentals. Members of the Aster family, they are closely related to sunflowers. Pyrethrum daisies are also the source of a very powerful and effective pesticide. Known as pyrethrin, it is among the safest pesticides available and is used worldwide. Because it is a natural pesticide, pyrethrin is a good choice in organic farming.
Perennial plants with a classic daisy appearance, pyrethrum daisies have a yellow center and white petals on long, thin, rigid stems. The leaves of the plant are blue-green in color. Pyrethrum daisies can grow to 60 cm in height. They grow well in hardiness zones 3 through 7. The plant prefers well-drained soils and thrives in partial shade or full sun.
The plant has been used for centuries as an insecticide in the Middle East. It has also been used as a remedy for lice, known as Persian insect powder or Persian pellitory. In the 19th century it was widely sold under the brand name Zacherlin. After World War II, pyrethrum-based insecticides became very popular and are still in common use today.
The flowers and seed pods of the plant are harvested, dried and pulverized. Oleoresins are then extracted from the plant. These contain the active component that acts as an insecticide, known as pyrethrin. Pyrethrin can be suspended in water, oil or delivered as a powder.
Pyrethrin is considered to be among the safest of insecticides. It is much less toxic to humans and pets than most synthetic insecticides. It is also nonpersistent and biodegradable, breaking down quickly on exposure to sunlight. Natural pyrethrin can also be combined with synthetic chemicals, such as piperonyl butoxide, to significantly enhance the toxicity of the insecticide. Formulation of this kind is referred to as synergized pyrethrin.
Effects on Insects
Pyrethrin is a neurotoxin, attacking the nervous system of all insects. In lower concentrations, pyrethrin also acts as an insect repellent and can deter female mosquitoes from biting. The pesticide is effective against many types of pests, including ants, bedbugs, fleas, lice, roaches, silverfish, mites, mosquitos and ticks.
Pyrethrin vs. Pyrethroids
Pyrethrin should not be confused with pyrethroids. Pyrethroids are synthetic insecticides based on natural pyrethrum. A common example of a pyrethroid insecticide is the preparation Permethrin. These synthetic substances tend to be more persistent and can result in residual toxicity, which does not occur in the natural form of the insecticide.