Using Neem for Pest Control

By Therese Ciesinski, GardenSMART

Ever heard of neem? This odd name belongs to a tree with superb pest-fighting abilities. If you have bugs eating your garden, add neem to your insect-control strategy. Unlike synthetic chemical pesticides, neem residue is harmless to non-target insects, people, or animals, and doesn’t build up to toxic levels in the soil.

What It Is

Neem is a naturally occurring pesticide made from an extract of the fruit and seeds of the neem tree (Azadirachta indica). An evergreen tree in the mahogany family that grows in India and Africa, neem has been used to control insects for thousands of years.

Neem leaves and fruits. Photograph by Kevinsooryan, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons.

It can be used on flowering plants, herbs, vegetable and fruit plants, even houseplants.

You can use neem indoors, too. And since it affects pests at every life stage, it can be used year-round.

You can buy neem in ready-to-use form, and as an oil concentrate that you mix with water and dish soap (to help the oil stick to leaves) and use as a spray or a soil drench.

Research indicates that neem granules can be added as a soil amendment, adding nutrients, boosting microbial activity and helping to inhibit fungal diseases.

What Is It Used For

Neem kills soft-bodied insects, including aphids, spider mites, scale, mealybugs, caterpillars, thrips, white flies, and leaf hoppers. When used as a soil drench, it kills soil-dwelling root-knot nematodes.

It affects pests at every stage of growth, from egg to adult. Because it works in different ways on each life stage, insects don’t become immune to neem.

Neem is safe for humans, pets, and wildlife. When sprayed, it will kill both pest and butterfly caterpillars, and the larva of beneficial insects, so be sure you know whether an insect is a pest before spraying. It will also kill bees and other beneficials if sprayed directly on them. And neem is toxic to fish and aquatic life, so don’t use it near waterways.

How It Works

Neem only works when wet. When it dries it is not effective. The pests must be present and sprayed to be killed.

Neem doesn’t kill insects on contact, however. It suffocates them or disrupts their feeding. Then, depending on their life stage, they starve to death, or if eggs, don’t hatch.

How To Use

Spray both sides of the leaves of the affected plant. Wetting the underside of the leaf is important. That’s where caterpillars often hide and eggs laid.

Since neem is an oil, you must shake the container frequently to keep the contents from separating.

When using a concentrate, only mix up as much as you’re going to use at that time. Diluted neem loses its efficacy.

Tips For Using

Spray in the morning or evening when beneficial insects aren’t as active.

Don’t spray if it’s very hot or the sun is very bright; plant foliage may burn.

Avoid spraying flowers if you can; concentrate on the leaves. And avoid spraying young plants and transplants.

If you’re unsure if a plant can tolerate neem, test it on a leaf first to see whether there’s a reaction, such as burning.

Things To Know

Neem is biodegradable; once dry it breaks down to harmless compounds. While that means it’s safer and doesn’t build up in the soil, it also means you have to reapply it.

Results aren’t instantaneous. It can take a couple of days before you see a reduction in pest populations.

Neem is also a fungicide. It can help prevent or treat blackspot, rust, leaf spot, anthracnose and scab. Spray every seven to ten days as a preventative. To treat existing fungal infections, spray every seven days until the fungus is gone. Repeat every two weeks to keep it from coming back.

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