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Pyrethrum was a genus of several Old World plants now classified in eitherChrysanthemum orTanacetum which are cultivated as ornamentals for their showyflower heads.Pyrethrum continues to be used as a common name for plants formerly included in the genusPyrethrum. Pyrethrum is also the name of a naturalinsecticide made from the dried flower heads ofChrysanthemum cinerariifolium andChrysanthemum coccineum. The insecticidal compounds present in these species arepyrethrins.
Some members of the genusChrysanthemum, such as the following two, are placed in the genusTanacetum instead by some botanists. Both genera are members of the daisy (or aster) family,Asteraceae. They are allperennial plants with a daisy-like appearance and whitepetals.
The flowers are pulverized and the active components, called pyrethrins, contained in the seed cases, are extracted and sold in the form of anoleoresin. This is applied as a suspension in water or oil, or as a powder. Pyrethrins attack the nervous systems of all insects, and inhibit female mosquitoes from biting. When present in amounts less than those fatal to insects, they still appear to have aninsect repellent effect. They are harmful to fish, but are far less toxic to mammals and birds than many synthetic insecticides and are not persistent, beingbiodegradable and alsodecompose easily on exposure to light. They are considered to be amongst the safest insecticides for use around food. In 1998 Kenya was producing 90% (over 6,000 tonnes) of the world's pyrethrum, calledpy for short. Production in Tanzania and Ecuador is also significant. Currently the world's major producer is Tasmania, Australia.
Pyrethrum has been used for centuries as aninsecticide,[1] and as a lice remedy in theMiddle East (Persian powder, also known as "Persian pellitory"). It was sold worldwide under the brandZacherlin by Austrian industrialistJ. Zacherl.[2] It is one of the most commonly used non-synthetic insecticides allowed in certified organic agriculture.[3]
The flowers should be dried and then crushed and mixed with water.
A pheromone produced by these plants attracts ladybug beetles, and at the same time acts as an alarm signal to aphids.[4]
Rat and rabbitLD50 levels for pyrethrum are high, with doses in some cases of about 1% of the animal's body weight required to cause significant mortality. This is similar to fatal levels in synthetic pyrethroids.[5] Nevertheless, pyrethrum should be handled with the same caution as synthetic insecticides:[6] safety equipment should be worn, and mixing with other chemicals should be avoided.[7]
People can be exposed to pyrethrum as a mixture ofcinerin,jasmolin, andpyrethrin in the workplace by breathing it in, getting it in the eyes or on the skin, or swallowing it. TheOccupational Safety and Health Administration (OSHA) has set the legal limit (Permissible exposure limit) for pyrethrum exposure in the workplace as 5 mg/m3 over an 8-hour workday. TheNational Institute for Occupational Safety and Health (NIOSH) has set aRecommended exposure limit (REL) of 5 mg/m3 over an 8-hour workday. At levels of 5000 mg/m3, pyrethrum isimmediately dangerous to life and health. People exposed to pyrethrum may experience symptoms includingpruritus (itching),dermatitis,papules,erythema (red skin),rhinorrhea (runny nose),sneezing, andasthma.[8]
Pyrethrum, specifically the pyrethrin within, is highly toxic to insects including useful pollinators like bees. The risk of killing bees and other beneficial insects is partially reduced by the compound's rapid breakdown (a half-life of approximately 12 hours on plants and on the surface of the soil, with about 3% remaining after five days, but persisting several weeks or more if it enters a body of water or is dug into the soil) and its slight insect-repellant activity.[9]
Common names forChrysanthemum cinerariifolium include:
Common names forChrysanthemum coccineum include:
"I've also marked my pyrethrum bottle 'for pesticides only'. I have another one for herbicides. It doesn't matter whether you're organic or not, accidents can happen. It's best to keep these chemicals apart." As a precaution, safety gear should be worn when using pyrethrum.
