How to use neem oil and its extracts to stop most insect pests organically.
Neem oil, one of nature’s best ways to deal with problem insects, is pressed from the fruits, seeds and bark of an evergreen tree (Azadiracta indica) that grows in South Asia, especially India, and parts of Africa. The tree’s oil, known in Sanskrit as Sarva Roga Nirvani or “cure of all ailments,” has a long history of skin-care and medicinal uses. Because of its nourishing, acne-fighting qualities, it’s often found in specialty soaps and other modern skin products.
Neem is best known as an organic method for controlling insect pests. The compounds contained in the oil work in many ways against many insects, interfering with their reproductive cycles, inhibiting their feeding, serving as a repellent, and, with some pests, as a contact-insecticide that kills them outright.
Neem oil, applied as a foliar spray or “shine,” is especially valuable to indoor and hydroponic growers. The spray prevents fungus and other leaf diseases. It’s particularly effective against spider mites, indoors and out.
Neem Oil and Its Compounds
Most neem oil comes from the tree’s crushed seeds mixed with a solvent such as alcohol or with water. As with cooking oils, cold-pressed neem oil is best for organic gardening purposes. The different methods of processing determines the strength of the oil’s active ingredients.
Azadirachtin is the most common compound extracted from neem seed and other parts of the tree. Azadirachtin is combined with soaps or other organic-listed compounds in all-around insect sprays. It’s also available as a stand-alone extract to combat various kinds of mites, moth larvae and beetles. It works by disrupting the pest’s hormones that control breeding, growth and feeding.
Azadirachtin isn’t the only compound in neem oil thought to be useful in pest control. Cornell University’s Resource Guide For Organic Insect and Disease Management (see below) says that oil from the neem tree contains over 70 compounds in its oil, many of them thought to have insecticidal or repellant properties. The Resource Guide cites a 1995 Washington State University study that showed products containing “both azadirachtin and neem oil have greater efficacy in controlling aphids than either ingredient alone.”
Insects That Neem Controls
Pests affected by neem and its extracts include some of the most common and difficult-to-control insects that gardeners face. According to The Gardener’s Guide To Common-Sense Pest Control, these include the Colorado potato beetle, Mexican corn beetle, whitefly, spotted cucumber beetle, corn earworm, flea beetle, and cabbage looper.
It’s also been shown to repel and disrupt life cycles of spider mites and root-knot nematodes. These life cycle disruptions lead to reduced populations and eventually extermination. Overall, neem is reported to inhibit feeding of 170 insect species and inhibited growth of insect species in four different orders. In addition, it’s directly toxic to aphids, termites, and various caterpillars.
Surprisingly, neem is thought not to harm certain beneficial insects including predatory mites, and does not impact honey bees and other pollinators as long as they’re not sprayed directly. Earth worms are also unaffected by neem compounds. The National Pesticide Information Center reports that neem is practically non-toxic to birds and mammals.
Because neem contains so many active ingredients and works on insects in a variety of ways, it’s believed that insects will not develop a tolerance to it even with extended use.
How To Use Neem
Because it can disrupt insect growth and feeding patterns, neem is best used when insects are young and in early stages. Neem doesn’t work immediately when it affects insects this way. Don’t expect to see instant die-offs but do look for a decrease in pest numbers. Neem takes time to work. Use neem sprays frequently. Neem lasts only a few days in the environment so weekly sprayings are recommended. Be sure to spray on both sides of leaves.
Mix concentrates as directions specify. As an oil, neem does not dissolve, nor does its compounds. Be sure to stir neem mixtures frequently to maintain strength. Make no more than you’ll use. Neem, once diluted, doesn’t keep long. Have extra when done applying? Spray liberally on cucumber plants to discourage disease.
Neem oil may also be used on the ground where it will be taken up by plants. While neem persists longer when taken up by plants than it does sprayed on its surface, it still doesn’t stay effective long. Refrain from using ground applications a week before harvesting any plant meant for consumption. It’s reported that the strongly bitter neem can affect flavor.
Applying neem oil to plant starts before they are set out in the garden makes the plants less likely to experience problems down the road.
More Information
The comprehensive Resource Guide For Organic Insect and Disease Management from Cornell University is a dependable, online resource for dealing with all kinds of pest problems (PDF).
India’s Neem Foundation offers history, background, and discussion of a host of current and potential uses for products from the neem tree as well as current research. Fascinating.
Click here to view the embedded video.
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