Taking an environmentally sensitive approach to pest management
The pyrethrum daisy is a natural insecticide extracted from the oil glands on seeds of the perennial plant, Tanacetum cineariaefolium. Today the pyrethrum extract is used in various home and garden products, certified organic products, in disinfestation treatments, and for public health uses such as mosquito control. Pyrethrum can be used for aphids, scale, spider mites, and thrips. Pyrethrum can also be combined with neem oil or insecticidal soap for broad spectrum control.
The first record of the pyrethrum daisy was 2000 years ago at the time of China’s Chou Dynasty. The flower was grown in the Dalmatian region (presently Croatia) and traded along the Silk Route. During the Napoleonic Wars (1804-1815) crushed flowers were used by French soldiers to control flea and body lice. During World War I, pyrethrum was also made into a “Dalmatian Flea Powder”. From 1918 until 1940, Japan was the major producer of pyrethrum. Thereafter, Kenya and several other East African countries were major suppliers. Today, vegetative transplants are planted in the field in Kenya and flowers are hand-harvested, as many as 14 times during a season. Flowers are then dried and delivered to collection sites for payment. In East Africa, most pyrethrum plots are less than one acre.
Pyrethrum daisies have also been grown in Tasmania, Australia since 1932 and their production continues today with modernized cultural practices. In Tasmania, pyrethrum daisy plants are grown from seed. They require exposure to winter temperatures (i.e., vernalization) before flowers are initiated. Thus, plants from seed sown in winter 2007 will not be harvested until January 2009. Thereafter, pyrethrum is harvested annually in the summer for 3 successive years. Modified combine harvesters are used for the crop. The harvested product is primarily achenes (i.e., seeds), which are taken to a processing plant. At the processing facility, the achenes are hammer milled and pelletized and then the pyrethrum oil is extracted and refined. Despite these processes, pyrethrum from Tasmania is considered a natural product.
Pyrethroid insecticides are a synthetic class of chemicals whose structure is similar to pyrethrum. Because natural pyrethrum breaks down in light, pyrethroids were synthesized to be more stable in sunlight. Some of the pyrethroid insecticides include permethrin, cypermethrin, bifenthrin and deltmethrin. These chemicals are used in head lice shampoos, flea, tick, and mosquito products for dogs, and for mosquito control on outdoor clothing and camping gear. However, pyrethroids are not considered natural products. Also, pyrethroids are generally more toxic and more persistent in the environment than pyrethrum.
Pyrethrum is currently under review by the Environmental Protection Agency in the U.S. and Biocides Directive in the European Union, as well several other insecticides currently on the market. However, consumers may be optimistic about the future of pyrethrum because it has very low toxicity for humans and warm blooded animals and is rapidly degraded by ultraviolet light and air. These properties of pyrethrum provide growers with an alternative to other insecticides for the control of common garden pests.
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REVISED: November 16, 2012