Insecticidal Properties of Neem

The neem tree, native to India and Burma, has been used for centuries for both its medicinal uses and as a safe, organic insecticide. The Colorado State University Web site reports that an insecticide made from crushed neem seeds is effective in disrupting the growth of insects such as whiteflies and others. It’s available for purchase as a spray at some garden stores and online.

Neem Blocks Insects’ Hormones

Neem oil is a complicated chemical formula, according to DiscoverNeem.com. Because neem is not a poison, it acts on insects differently: it enters their bodies in much the same way that natural hormones do. However, neem blocks the effects of their natural hormones, causing them to stop eating, mating and laying eggs. In time, they will perish. The local insect population will diminish, breaking their reproductive cycle and resulting in a marked decrease in the number of troublesome insects.

Neem Affects Only Chewing and Sucking Insects

Savvy organic gardeners often make use of beneficial or predator insects to control populations of destructive insects. When chemical pesticides are used, they don’t discriminate about what type of insect they kill. Neem is different because direct contact with it only affects insects that suck the juices out of plants, such as aphids, scale and those that chew the leaves and other parts of plants, such as grasshoppers.

Neem’s Presence Causes Insects to Perish

Insects needn’t come into direct contact with neem oil spray in order for it to effectively stop them from eating your plants. DiscoverNeem.com tells of an informal study that was done where two grasshoppers were put in two separate jars. A leaf was sprayed with a chemical insecticide and placed into one of the jars, where the grasshopper ate it and immediately died. A second leaf was sprayed with neem oil and placed in the other jar. Although the grasshopper did not eat the leaf, it died within a few days, presumably from starvation. The mere smell of neem seems to deter insects from eating anything.

Systemic Pesticide

You can use a dilution of neem oil as a systemic insecticide by watering the soil around your plants with such a solution. Plant tissues will absorb the oil, making the entire plant effective in repelling destructive insects that find their way to the plant. Leaf hoppers and grasshoppers and other insects that eat more than just the outer layer of the plant’s leaves are affected more than other insects such as aphids, which typically dine on only the outer layer of plant parts. DiscoverNeem.com assures readers that the neem that is present in a plant will not harm humans when they eat it.

Neem Oil Smothers Insects

Many kinds of oil are used to smother insects such as aphids and scale, and neem oil is included in this list. Unfortunately, when you spray neem oil on beneficial insects, it will also kill them. DiscoverNeem.com recommends spraying your plants early in the day, before beneficial insects become active. The spray will dry as the day warms up and because beneficial insects eat other insects or their larvae and not your plants, the neem spray will not affect them.

Keywords: neem oil, natural insecticide, organic gardening

About this Author

Barbara Fahs lives on Hawaii island, where she has created Hi'iaka's Healing Herb Garden. Fahs wrote "Super Simple Guide to Creating Hawaiian Gardens," and has been a professional writer since 1984. She contributes to Big Island Weekly, Ke Ola magazine, GardenGuides and eHow. She earned her B.A. at UCSB and her M.A. from San Jose State University.