12 Oct

Neem Oil – Organic Pesticidal Spray & Soil Drench

Neem Oil

Neem Oil is extracted from Neem trees and contains a compound called Azadirachtin that is useful for fighting common plant pests such as fungus gnat larvae, spider mites, and grasshoppers (see larger list below). Once Azadirachtin has been ingested by pests, it acts as an appetite suppressor and growth inhibitor causing failure to molt and starvation.

Used as a soil drench, Neem Oil acts as an systemic pesticide, meaning the plant will absorb the Azadirachtin compound and distribute it throughout its vascular system.  Once distributed, any part of a treated plant a pest ingests will also contain the Azadirachtin.

Aphids

Aphids feeding on the juices of a plant stem.

Used as a foliar spray, the same principals of ingestion by insects still apply but primarily the Neem will act as a physical inhibitor to the insects by coating their bodies in the oil. By coating their bodies, the insect’s spiracles or “nostrils” become blocked and the insect suffocates.

Plant Pests Controlled with Neem:

Mealy bug

Aphids

Cabbage worms

Thrips

Whiteflies

Mites

Fungus gnats

Caterpillars

Locust (Grasshoppers)

Nematodes

Japanese beetle

Leafminers

Why Make Your Own?

The main reason we started making homemade Neem Oil spray is that most store-bought Neem sprays contain low levels of Azadirachtin, the primary ingredient responsible for pest control. Azadirachtin naturally degrades over time and can degrade within days if left at room temperature. Since most store-bought sprays sit at room temperature for several days or months before purchase, this can reduce the effectiveness by the time the product is used. Excessive heat exposure can also reduce effectiveness by breaking down the compound which is why it is important to buy Cold Pressed Neem Oil.

How to Make and Use Neem Spray

This is the recipe we use to help fight against fungus gnats and white and red spider mites in our nursery. This recipe is safe to use on plants but always test a small area before treating an entire plant or tray of seedlings.

Neem IngredientsNeem Oil Spray Recipe:

  • 1 liter of warm water.
  • 3-5ml Cold Pressed Neem Oil (use 3ml for preventative treatments and 5ml for infestations).
  • 3ml dawn dish soap (or other biodegradable soap) – this acts as an emulsifier which helps distribute the oil in the water. DO NOT include soap if using this spray for carnivorous plants.

Add all ingredients to a spray bottle and shake to combine. Apply as a foliar spray and soil drench every 3 weeks for prevention or every week for infestations. Shake the bottle often while applying to keep the oil distributed in the mixture.

Between mixing batches, remaining undiluted Neem Oil can be refrigerated for up to a year to slow the rate at which the Azadirachtin degrades.

A Note of Caution

CautionEach plant species can react differently to various pesticide formulas. If using Neem Oil as a foliar spray, test a single leaf before applying the spray to the whole plant to mitigate the risk of losing the plant if it responds poorly to the treatment. If using Neem as a soil drench, reduce the formula strength for the first treatment or only drench a single plant (if you have multiples of the same species) and see how the plant responds before increasing the concentration.

Sources:

Bond, C.; Buhl, K.; Stone, D. 2012. Neem Oil General Fact Sheet; National Pesticide Information Center, Oregon State University Extension Services.
Pesticide Information Profile: Azadirachtin, Cornell University.
Murray B. Isman “Botanical Insecticides, Deterrents, And Repellents In Modern Agriculture And An Increasingly Regulated World” Annual Review Of Entomology Volume 51, pp. 45-66.
Effect of Emulsion Size and Shelf Life of Azadirachtin A on the Bioefficacy of Neem (Azadirachta indica A. Juss) Emulsifiable Concentrates by Lalit Kumar and Balraj S. Parmar, Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi 110012, India. J. Published July 12, 2000. Copyright © 2000 American Chemical Society.

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