Pyrethrum
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Pyrethrum was a genus of several Old World plants now classified in either Chrysanthemum or Tanacetum which are cultivated as ornamentals for their showy flower heads. Pyrethrum continues to be used as a common name for plants formerly included in the genus Pyrethrum. Pyrethrum is also the name of a natural insecticide made from the dried flower heads of Chrysanthemum cinerariifolium and Chrysanthemum coccineum. The insecticidal compounds present in these species are pyrethrins.
Description
Some members of the genus Chrysanthemum, such as the following two, are placed in the genus
- Tanacetum cinerariifolium is 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 pyrethrin insecticides.
- Other species, such as C. balsamita and C. marshalli, also contain insecticidal substances, but are less effective than the two species mentioned above.
Insecticides
The flowers are pulverized and the active components, called pyrethrins, contained in the seed cases, are extracted and sold in the form of an oleoresin. 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 an insect repellent effect. They are harmful to fish, but are far less toxic to mammals and birds than many synthetic insecticides and are not persistent, being biodegradable and also decompose 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, called py for short. Production in Tanzania and Ecuador is also significant. Currently the world's major producer is Tasmania, Australia.
Sprays
Pyrethrum has been used for centuries as an
The flowers should be dried and then crushed and mixed with water.
- toxicityto insects and is faster acting compared with pyrethrins used alone. These formulations are known as synergized pyrethrins.
Companion planting
A pheromone produced by these plants attracts ladybug beetles, and at the same time acts as an alarm signal to aphids.[4]
Toxicity
Mammals
Rat and rabbit LD50 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 of
Other animals
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
Common names for Chrysanthemum cinerariifolium include:
- Pyrethrum
- Pyrethrum daisy
- Dalmatian pyrethrum
- Dalmatian chrysanthemum
- Dalmatian insect flower
- Dalmatian pellitory
- Big daisy
Common names for Chrysanthemum coccineum include:
- Pyrethrum
- Pyrethrum daisy
- Painted daisy
- Persian chrysanthemum
- Persian insect flower
- Persian pellitory
- Caucasian insect powder plant
See also
References
- ^ Bioaromatica The history of pyrethrum
- ^ US patent 308172, Johann Zacherl, "Pyrethrum Soap", issued November 18, 1884
- ^ Some Pesticides Permitted in Organic Gardening, by Laura Pickett Pottorff, Colorado State University Cooperative Extension, January 5, 2010.
- PMID 31087371.
- ^ Pesticide Toxicity Profile: Synthetic Pyrethroid Pesticides Archived 2021-04-22 at the Wayback Machine, by Frederick M. Fisher, University of Florida IFAS Extension Service, 2013
- ^ insecticide (botanical, mineral, synthetic) toxicity to mammals Electronic Data Information Source of University of Florida
- ^ "Using Pyrethrum". Gardening Australia. Australian Broadcasting Corporation. 25 May 2013. Retrieved 3 November 2018.
"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.
- ^ "CDC - NIOSH Pocket Guide to Chemical Hazards - Pyrethrum". www.cdc.gov. Retrieved October 23, 2015.
- ^ "Pyrethrins general fact sheet" (PDF). national pesticide information center.
External links
- National Pesticide Information Center: Pyrethrins and Pyrethroids Fact Sheet
- CDC - NIOSH Pocket Guide to Chemical Hazards
- EXTOXNET: Pyrethrins and Pyrethroids
- "What is Pyrethrum?" Archived 2011-01-24 at the Wayback Machine
- Role of aphid alarm pheromone produced by the flowers in repelling aphids and attracting ladybug beetles