Pyrethrumwas a genus of several Old World plants now classified in eitherChrysanthemumorTanacetumwhich are cultivated as ornamentals for their showyflower heads.Pyrethrumcontinues to be used as a common name for plants formerly included in the genusPyrethrum.Pyrethrum is also the name of a naturalinsecticidemade from the dried flower heads ofChrysanthemum cinerariifoliumandChrysanthemum coccineum.The insecticidal compounds present in these species arepyrethrins.
Some members of the genusChrysanthemum,such as the following two, are placed in the genusTanacetuminstead by some botanists. Both genera are members of the daisy (or aster) family,Asteraceae.They are allperennial plantswith a daisy-like appearance and whitepetals.
Tanacetum cinerariifoliumTanacetum cinerariifoliumis called the Dalmatian chrysanthemum, denoting its origin in that region of the Balkans (Dalmatia). It looks more like the common daisy than other pyrethrums do. Its flowers, typically white with yellow centers, grow from numerous fairly rigid stems. Plants have blue-green leaves and grow to 45 to 100 cm (18 to 39 in) in height. The plant is economically important as a natural source of pyrethrininsecticides.
Tanacetum coccineumC. coccineum,the Persian chrysanthemum, is a perennial plant native toCaucasusand looks somewhat like adaisy.It produces large white, pink or red flowers. The leaves resemble those offerns,and the plant grows to between 30 and 60 cm (12 and 24 in) in height. The flowering period is June to July in temperate climates (Northern Hemisphere).C. coccineumalso contains insecticidal pyrethrins, but it is a poor source compared toC. cinerariifolium.
Other species, such asC. balsamitaandC. marshalli,also contain insecticidal substances, but are less effective than the two species mentioned above.
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 repellenteffect. They are harmful to fish, but are far less toxic to mammals and birds than many synthetic insecticides and are not persistent, beingbiodegradableand alsodecomposeeasily 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, calledpyfor 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 brandZacherlinby 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.
Pyrethroidsare synthetic insecticides based on natural pyrethrum (pyrethrins); one common example ispermethrin.Pyrethrins are often sold in preparations that also contain the synthetic chemicalpiperonyl butoxide,which enhances thetoxicityto insects and is faster acting compared with pyrethrins used alone. These formulations are known assynergized pyrethrins.
Rat and rabbitLD50levels 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]
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]
^"Using Pyrethrum".Gardening Australia.Australian Broadcasting Corporation.25 May 2013.Retrieved3 November2018."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.
