Pyrethrum Effects
Pyrethrum, one of the safest insecticides for food crops, occurs naturally in two varieties of chrysanthemums. The Persian chrysanthemum from the Caucasus region of the Middle East is the least potent. A variety from the Balkans--the Dalmatian chrysanthemum--produces the most pyrethrins, the active poison. Both types of flowers are common ornamentals. The dried and powdered flower heads can be used as a homegrown insecticide, but commercial preparations are more dependable. Does this Spark an idea?
Effects
Pyrethrins are potent toxins that affect the nervous system of soft-bodied insects. As a powder or a spray, the poison is effective on common garden pests such as caterpillars and aphids. Pyrethrin decomposes over time, so for severe infestations, repeated applications are necessary. Pyrethrin is not toxic to mammals or birds, but will affect fish, reptiles and amphibians. Use near waterways is not advised because of the risk to wildlife.
Repellents
In doses too low to kill insects, pyrethrum still has effective repellent properties. The extract was once used as a remedy for lice, and also discourages the female mosquito from biting. Pyrethrum demonstrates this repellent effect even in doses too low to actually kill insects, and is the active ingredient in incense-style mosquito coils. Extracts repel ticks as well.
Companion Planting
The lacy foliage and daisy-like flowers of the Dalmatian and Persian pyrethrums make them popular companion plants in vegetable gardens. The presence of these plants near food crops like brassicas, which are very vulnerable to insect damage, can help prevent infestations. On the perimeter of a garden, a decorative planting of pyrethrum serves as a natural barrier to soft-bodied insect pests.
Home-Grown Pesticide
For those seeking an organic alternative to commercial products, the dried flower heads of pyrethrum can be crushed into powder or steeped to create a tea for spraying problem garden areas. Because pyrethrum breaks down quickly, it can be reapplied as needed without fear of producing resistance in the targeted insect species. Commercial products include sticking agents that act to prolong the contact with the pests. Homemade powders and teas are both short-lived and more difficult to apply effectively.
Commercial Products
Pyrethrum combined with piperonyl butoxide is more effective and more potent than the natural product alone. Raid, a well-known household insecticide, is based on that chemical combination. Many common flea and tick treatments for pets contain potent concentrations of pyrethrum, as do treatments for human head lice. Pyrethrum powder is available in bulk for use in gardens. Mosquito foggers are also often based on this natural toxin.
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