What are some natural insecticides?

Despite the well-meaning wishes and efforts of many organic gardeners, there comes a time when insecticides must be used to eliminate the insects that infest and destroy crops. Many prefer to use a natural insecticide rather than a synthetically produced chemical insecticide. Rotenone and pyrethrum are well-known and widely used natural insecticides derived from plants. Other natural insecticides include nicotine, neem oil and soap.

Rotenone and pyrethrum are commonly used as natural insecticides. Rotenone is derived from the roots of tropical and subtropical plants of the genus derris . Rotenone acts as a natural, broad-spectrum insecticide that poisons both by contact and by ingestion. Rotenone is commonly used as a powder or spray, and while it is not toxic to plants, it is highly toxic to fish and moderately toxic to warm-blooded mammals.

Pyrethrum is derived from the Dalmatian chrysanthemum and is used in powder or liquid suspension form. In high concentrations, it acts as a natural insecticide, attacking an insect's central nervous system. Pyrethrum in small concentrations may not be toxic to insects, but retains the ability to repel insects. Pyrethrum is toxic to fish but less toxic to mammals than synthetic pesticides. It is biodegradable and breaks down easily on exposure to light.

Some organic gardeners recommend using soap, which has been used as a natural insecticide for hundreds of years. Diluting liquid dishwashing detergent such as Ivory with water to a 1-2% solution that can be sprayed to cover plants has been shown to be effective in controlling insects. Be careful, however, as repeated and thorough coverings with high concentrations of soap can cause damage to certain types of plants. Soap as a natural insecticide can be far less toxic to humans and animals than other alternatives, but it can also be far less effective, especially when treating an infestation.

While nicotine, neem, and other botanical insecticides not discussed here have been shown to be effective with minimal to moderate success, any type of natural insecticide should be used as little as possible. Just because you use a natural insecticide instead of a synthetic one doesn't mean it's any less harmful to animals or humans. Application of any type of natural insecticide should be done safely and only as often as necessary to maintain a healthy fruit or vegetable crop.

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