Pyrethrum daisies have quite pretty flowers and are therefore often grown as ornamentals. Pyrethrum daisies are a natural source of a very powerful and effective pesticide known as pyrethrins which is one of the safest pesticides available today.
Pyrethrum is a highly effective insecticide, used for centuries against all varieties of insect pests. Tasmania is now the world’s largest producer of pyrethrum, exporting to the world for use in a wide range of insecticidal preparations. Pyrethrum is harmful to fish, but far less toxic to mammals and birds than many synthetic insecticides and are not persistent, being biodegradable and it decomposes easily on exposure to light. Pyrethrum is considered to be amongst the safest insecticides for use around food.
The six different pyrethrins that make up the naturally occurring “pyrethrum” is concentrated in the flower heads. Pyrethrum is a unique insecticide in that, used correctly, it is safe for use near humans and warm blooded animals, in kitchens and restaurants, food processing factories and other sensitive environments.
Pyrethrum affects the insects’ central nervous systems, disrupting normal functions, so that nervous impulses fail.
In the lowest concentrations, pyrethrum affects insect behaviour, producing an avoidance reaction. At slightly greater concentrations, pyrethrum makes insects lose their normal behavioural patterns, causing them to abandon their hiding places and come out in the open, and then to die.
Because of the insecticidal properties of pyrethrum daisies they are useful as companion plants, to repel pest insects from crops and garden plants. They are thought to repel aphids, cockroaches, flies, mosquitoes, bed bugs, leafhoppers, spider mites, harlequin bugs, ticks, amongst other insects that are in our gardens and homes.
Pyrethrins (pyrethrum) were originally derived from the East African chrysanthemum flowers and have insecticidal activity. In natural environments they are chemically unstable and break-down rapidly when exposed to air and sunlight.
In the 1970s, synthetic pyrethroids came into the market for agricultural purposes as they were synthesized from petroleum derivatives.
Their desirable features are:
Formulations that are commercially available include aerosols, emulsifiable concentrates, wettable powders, granules, and concentrates for ultra low volume applications; example – targeting mosquitoes. Their mode of action is interference with transmission of nerve impulses.
Synthetic Pyrethroids are one of the least acutely toxic insecticides to mammals because they are quickly deactivated by metabolic processes.