Neem Oil

Neem oil is extracted from the seeds of Azadirachta indica, an evergreen tree native to India. It was used in traditional Ayurvedic medicine to treat a variety of external skin conditions, but its primary use worldwide is now as an organic pesticide and insect repellent. Neem’s great effectiveness as an organic pest control make it a prized agricultural cash crop that is grown throughout the tropics.

Undiluted, it is dark red, very bitter, and very stinky, but most neem sold in garden centers and home improvement stores are diluted blends which minimize its less pleasant aspects.

Neem is an effective organic pesticide against many insects as well as a variety of fungal and viral plant diseases. It is safe to use around pets and will not harm beneficial insects including ladybugs and honeybees, because it works in a fundamentally different way than most chemical pesticides.

Neem works in three ways:

• It acts as an anti-feedant because it tastes so bad. Some insects will would rather starve than eat it.
• It contains many complex compounds which act as hormone disruptors in the insects which ingest it, namely the chewing and sucking insects (see the chart below). It usually does not kill the insect outright, but causes it to lose its survival behaviors – the insect may stop eating, mating, laying eggs, or flying. Once the reproductive cycle is interrupted, the insect’s life cycle is broken, and the population soon dies out.
• It suffocates the insect. This effect occurs when you spray neem oil directly on the insect’s body (it works well this way on aphids). Unfortunately as an oil, it will also suffocate the beneficial insects, so try not to douse your ladybugs, too.

Because honeybees, ladybugs, parasitic wasps and other beneficial insects do not eat leaves or suck sap from within the plant, they do not ingest the neem and so are not affected. However, don’t spray neem oil directly onto flowers that honeybees are visiting.

As an organic pest control neem is effective against:

• Aphids
• Leafminers
• Beet armyworms
• Mealy bugs
• Beetles (including flea beetles)
• Mites
• Cabbage worms
• Moth larvae
• Caterpillars
• Nematodes
• Fungus gnats
• Thrips
• Grasshoppers
• Whiteflies
• Japanese beetles

Don’t expect neem oil to work instantly and find piles of dead bugs in the morning. Act early when you discover a problem, and give it a bit of time. Spray neem early in the morning to avoid suffocating beneficial insects, which are most active in the middle of the day. Neem is much kinder to the overall ecosystem of the garden than almost any other insecticide or repellent out there.

Neem is also a powerful antifungal and antiviral, making it also effective against the following plant diseases:

• Black Spot (Roses)
• Powdery mildew
• Anthracnose
• Rust (fungal)

Neem oil is available from Gardener's Supply using the link in the upper right of this page.