Insecticide in Plants

• This leaf beetle could be killed by plant-derived insecticides. altrendo nature/Stockbyte/Getty Images

  Some plants contain chemicals that are toxic to insects. Many of these insecticides are commercially available and registered with the Environmental Protection Agency. Insecticides from plants should be used after nonchemical control methods fail as an alternative to save your plants. New Mexico State University Cooperative Extension states that organic gardeners sometimes use natural insecticides from plants instead of synthetic organic chemicals. Plant-derived insecticides have low toxicity to mammals, including humans.

Neem (Azadirachta indica)

• Neem oil is extracted from the neem tree. Seeds from the neem tree contain high concentrations of azadirachtin. There are commercial neem products registered by the EPA. These products are useful against moths and butterflies, and their larvae since they cause larvae to not grow out of the larval stage. According to Rex Research, neem is also effective in controlling more than 100 insect pests.

Chrysanthemum (Chrysanthemum cinerariaefolium)

• Chrysanthemum contains pyrethrum, which is extracted from the plant's flowers. Pyrethrum is low-level toxic and it causes rapid paralysis of most insects. The insects will recover unless pyrethrum is used with piperonyl, butoxide or piperonyl cyclonene. Chemical sprays containing pyrethrum in combination with other insecticides are commercially available and registered with the EPA. Some common insects that sprays are effective against are aphids, coffee bugs, Colorado beetle, flea beetles, grasshoppers, cabbage worm, caterpillars, beetles, locusts, mites, moths and thrips.

Tobacco (Nicotiana tabacum)

• Tobacco contains nicotine, which is effective in controlling piercing-sucking insects such as aphids, whiteflies, leafhoppers and thrips. Nicotine extracted from tobacco is sold as 40 percent liquid concentrate of nicotine sulfate. The concentrate is diluted with water and applied as a spray. Apply it in warm weather for best results. Nicotine insecticides degrade quickly and can be applied near harvest time. It is registered with the EPA for use on vegetable and fruit crops.

Derris (Derris trifoliate)

• Derris plants contain rotenone, which is a general garden insecticide that is harmless to plants but highly toxic to many insects. Rotenone is moderately toxic to mammals, but it does not leave a harmful residue on vegetables. It acts as a contact and stomach poison for insects but loses its effectiveness after one week. Rotenone can be bought as dusts or sprays to control aphids, beetles and caterpillars.