Neem is a botanical insecticide derived from a tree native to the Middle East, where it has been used for centuries to control insects. One of the most desirable properties of neem is it's low degree of toxicity; it is considered almost nontoxic to humans and animals, and is completely biodegradable. It is used as an ingredient in toothpaste, cosmetics, pharmaceuticals, and other products. Neem products can be used to manage pests on vegetables, fruit, ornamentals, and lawns and can be found at many home garden centers.
Neem has been advertised as effective or moderately effective for more than 200 pest insect species and some of the plant diseases, including certain mildews and rusts. Effectiveness, however, is variable and test results have been inconclusive in many cases. Because the products are relatively new, it is not yet clear how effectively the products control each of these pests. Generally, chewing insects are affected more than sucking insects. Insects that undergo complete metamorphosis are also generally affected more than those which do not undergo metamorphosis. (Insects with complete metamorphosis look very different in the immature stage than they do as adults. e.g. moths, which are caterpillars in the immature stage. In insects that do not undergo metamorphosis the adult looks similar to the immature stage, e.g. grasshoppers)
Neem has been used with variable results to manage aphids, boxelder bugs, armyworms, cabbage loopers, Colorado potato beetles, mites, corn ear worms, cutworms, corn borers, flea beetles, fungus gnats, flies, grasshoppers, leafhoppers, leafminers, mites, spruce budworms, tent caterpillars, thrips, whiteflies, and many others. Scales and mealybugs are usually not affected, except by the newer 90% neem oil formulations which physically smother the insects. (Horticulture oils work the same way and may be less expensive.) Grasshoppers, leafhoppers, and plant hoppers vary in susceptibility. Aphids and thrips are not highly susceptible to neem, but are sometimes controlled with repeated applications. Neem often works slower than other pesticides, and effectiveness is reduced in cooler climates. Neem does not persist in the environment and should be reapplied after rain.
Neem has little effect when applied directly on insects, except in the oil formulations; most insects are affected only after consuming foliage that has been treated. Neem is most effective as a foliar spray applied periodically to new flushes of growth. On some species of plants neem also works as a systemic pesticide, absorbed into the plant and carried throughout the tissues, ingested by insects when they feed on the plant. This may make it effective against certain foliage-feeders that cannot be reached with spray applications, such as leafminers and thrips. Neem has some systemic activity when applied as a foliar spray, but it seems to work best as a systemic when applied as a soil drench, absorbed by the plant roots. It is not known how effective neem soil drenches are for larger ornamentals and trees, so drenches are usually recommended for smaller plants. Alkaline soils, such as we have in most of Montana, reduce the effectiveness of neem drenches. Neem products such as Azatin, Align, Turplex contain 3% azadiractin, the active ingredient in neem. This is the highest concentration among neem products currently available, but these products are often difficult to find. BioNeem, Neemix, and others, all contain less than 1% of the active ingredient.
Cranshaw, W. 1995. Management Recommendations for Insect Pests of Trees and Shrubs. Colorado State Univ, Ft. Collins, CO. Extension publication XCM-38. 78 pp.
Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California. Oakland, CA 94608- 1239. Pub. #3332. 276 pp.
The IPM Practitioner. Bio-Integral Resource Center. Berkeley, CA 94707.
Olkowski, W., S. Daar, and H. Olkowski. 1991. Common-Sense Pest Control; Least-toxic Solutions for Your Home, Garden, Pets and Community. Taunton Press, Newtown, Connecticut. 715 pp.
Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
Categories: Neem, Botanical insecticide