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Neem (Azadirachta indica)

Two types of botanical pesticides can be obtained from seeds of the Indian neem tree. Neem oil, obtained by cold-pressing seeds, can be effective against soft-bodied insects and mites but is also useful in the management of phytopathogens. Apart from the physical effects of neem oil on pests and fungi, disulfides in the oil likely contribute to the bioactivity of this material. More highly valued than neem oil are medium polarity extracts of the seed residue after removal of the oil, as these extracts contain the complex triterpene azadirachtin. Neem seeds actually contain more than a dozen azadirachtin analogs, but the major form is azadirachtin.

 

Target Pests: Spider Mites, Aphids, Thrips, Whiteflies, Fungus Gnats, Russet Mites, Broad Mites

Target Pathogens: Powdery Mildew, Black Spot, Downy Mildew, Anthracnose, Rust Fungus, Leaf Spot, Boytris, Blight, and Alternaria

Mode of Action: Neem products are complex mixtures of biologically active materials, and they are difficult to pinpoint the exact modes of action of various extracts or preparations. In insects, neem is most active as a feeding deterrent, but in various forms it also serves as a repellent,
growth regulator, oviposition (egg deposition) suppressant, sterilant, or toxin. As a repellent, neem prevents insects from initiating feeding. As a feeding deterrent, it causes insects to stop feeding. As a feeding, either immediately after the first “taste” (due to the presence of deterrent taste factors) (Salama and Sharaby 1988), or at some point soon after ingesting the food (due to secondary hormonal or physiological effects of the deterrent substance). As a growth regulator, neem is thought to disrupt normal development interfering with chitin synthesis. Susceptibility to the various effects of neem differs by species. Active neem constituents can be absorbed through plant roots and systemically move upward through the plant in xylem tissues.

Application Tips: Apply neem oil only in indirect light or in the evening to avoid the product burning foliage. Ideal conditions are to apply neem in the evening or when the lights go out. Application of neem in early morning hours is possible depending on the intensity of sunlight. Cannabis plants will be badly burned if neem is applied in direct light. Neem oil needs to be in liquid form when mixing and typically requires a surfactant (soap) to suspend it in solution. In cold weather climates that means warming the oil to re-liquefy it. Dr. Bronners peppermint lavender soaps work synergistically, acting as an additional botanical pest repellent.

Impact on Beneficial Insects

  • Overall toxicity rating: Low To Moderate
  • Specific impacts: predatory mites (Moderate), parasitoids (Low To Moderate), general predators (Low To Moderate)

References

University of Connecticut, Integrated Pest Management Program. 2011

University of California Statewide IPM Program

The Neem Tree: Source of Unique Natural Products for Integrated Pest Management, Medicine, Industry and Other Purposes. Schmutterer H.VCH Pappelallee No.3, P.O. Box 101161,Weinheim, 0-69451 Germany,1995.696pp. US $125 (OM 198). ISBN: 3-527-30054-6. 

Resources Guide for Organic Insect and Disease Management; Cornell University. Caldwell, Sideman, Seaman, Shelton, Smart, 2013.

Clemson University Cooperative Extension

Phytopathology and Plant Protection 43(7):700-711 · May 2010