Gardeners have used neem oil to control pests for hundreds of years. Neem oil is an organic pesticide extracted from the seeds of the neem tree (Azadirachta indica), which grows in the tropical forests of Burma, India and Sri Lanka. It is effective against a variety of pests, mites and certain fungal diseases. Maintaining healthy plants is the first defense against pest problems, but sometimes control measures are necessary. As with any pesticide, it is important to understand how to use neem oil on plants to control pests, as well as the benefits and limitations of available products.
How does Neem Oil work?
Neem seeds contain several compounds, but the most effective at controlling pests is azadirachtin. This compound reduces insect feeding and inhibits the growth and development of larvae. It also acts as a repellent, and like other horticultural oils, it can suffocate soft-bodied insects and mites by coating their bodies with the oil. Neem oil is most effective against larvae, but it also affects the feeding of adult insects. Targeted pests include whiteflies, thrips, caterpillars, aphids, mealybugs, spider mites, and larval scale insects.
Neem can also be used to manage some fungal diseases by preventing fungal spores from germinating and penetrating leaf tissue. Although it cannot cure already infected plant tissue, it can help reduce the spread of infection to healthy tissue. For this reason, neem is most often used to prevent powdery mildew.
Benefits of Neem Oil
This pest control treatment has many benefits that make it an attractive option for dealing with common plant pests.
Neem Oil is Safe for Pets and People
Neem oil is a safe and effective insecticide that can be used both indoors and outdoors. It is considered safe for humans and pets, so you can use it to get rid of aphids and mold gnats on your houseplants without worry.
Neem oil has little effect on beneficial insects and animals
Outdoors, neem oil has very low toxicity to beneficial organisms such as bees, birds and mammals. However, to avoid direct contact, it is always best to apply the insecticide early in the morning when bees and other pollinators are less active. It is not known to have any adverse effects on earthworms and can be used as a soil spray to control certain pests such as root nematodes.
Neem Oil is Biodegradable
Neem oil is biodegradable and breaks down quickly in soil, water and plant tissue. In fact, many neem oil products are certified organic by OMRI.
What plants should I use neem oil on?
Neem oil products are labeled for use on a variety of crops, including ornamentals, vegetables, fruits, and other plants. Check individual product labels for a complete list of approved plants.
Neem oil is generally safe to use, however some plants are sensitive to horticultural oils and soaps. Therefore, we recommend testing the product on a small area before treating the entire plant. Wait 24 hours after application to check the treated area for signs of damage. If no discoloration or leaf burn is observed, you can proceed to treat the entire plant.
Neem oil is not recommended for recently transplanted plants, certain thin-leafed herbs and leafy greens, or stressed plants, as these may be particularly sensitive.
Neem oil is best for pest control
There are many different formulations of neem oil available at garden centers, but not all of them are equal. To determine which type of neem oil to buy, look at the active ingredients listed on the bottle. There are three main types of neem oil formulations: hydrophobic extract of neem oil, azadirachtin, and cold-pressed neem oil.
It is important to note that the most widely distributed formulations, i.e. those with hydrophobic extracts of neem oil as their active ingredient, do not contain azadirachtin. Lacking the insecticidal properties of azadirachtin, these products work by smothering insects and coating the leaves with oil to combat foliar diseases, but do not inhibit the growth and development of insects. However, some of these are mixed with other insecticides, such as pyrethrins, to achieve a stronger control effect.
There are also products on the market that contain pure extracts of azadirachtin. These tend to be commercially produced and are often expensive, so the best products for home use are those that contain cold-pressed neem oil, which contains azadirachtin, as its active ingredient.
How to use neem oil
There are two ways to apply neem oil: spraying and applying it to the soil. Check out these steps to safely apply neem oil to your plants.
Dilute the neem oil according to the product instructions.
Neem oil is usually sold in a concentrated formulation that must be diluted before use, typically by adding a small amount of concentrated neem oil to a gallon of water for dilution.
Use as a spray or soil application
If you use neem oil as a foliar spray, mist the entire plant, covering the undersides and tops of leaves and stems. Be sure to spray liberally on the undersides of leaves, where pests often hide.
Neem oil is generally safe to use, but some people may be sensitive to it if they come into direct contact with it. Wear gloves and a mask to protect sensitive skin and lungs.
Another way to apply neem oil is as a soil spray, which involves pouring a diluted solution directly into the soil. This is an effective method for controlling fungus gnats, nematodes, and other soil-borne pests. When applied to the soil, the compound azadirachtin is also absorbed by the plant through the roots and acts as a mild systemic insecticide against certain insects (such as aphids) that suck the plant's juices and feed on the leaves.
Reapply if necessary
Neem oil sprays should usually be applied a second time 7-10 days after the first application. If you apply neem oil dip sprays, you should apply again after a week if there is an infestation and every 3 weeks to prevent pests.
How to Dilute Neem Oil for Use
Cold pressed neem oil is highly concentrated and must be diluted before use. The correct dilution method is as follows:
Choose the right size container
If you are treating just a few plants, a 1-quart spray bottle will suffice, but if you are treating larger quantities of plants, use a 1-gallon pump sprayer.
Remember that neem oil breaks down quickly, so do not mix more than you would use for one application, and mix a new amount if you are going to use it repeatedly.
Follow manufacturer's instructions for dilution
Always follow specific mixing instructions on the product label to avoid under- or over-spraying your plants.
Mixing Garden Soap
Add a small amount of horticultural soap or plant-safe liquid soap to the suspension as an emulsifier to help the water and oil mix. First, mix the water and soap together. Use 1 teaspoon of soap per gallon of water, reducing the amount of soap to 1/4 teaspoon for a 1-quart spray bottle.
Add neem oil
After mixing the water and soap, add a small amount of neem oil — 1 to 2 tablespoons per gallon of water, or 1 to 2 teaspoons per quart of water. Apply the mixture to a small test area of the plant before treating the entire plant.
Solutions for soil drench should be prepared in the same way as solutions for foliar sprays, but larger volumes may be required depending on the intended use.
Please be patient while waiting for your results and reapply if necessary.
You may see some initial reduction in pests due to the smothering effect of the oil itself, but the effect of azadirachtin on insect feeding and growth is not immediately apparent. So don't be discouraged if the problem doesn't go away overnight. Instead, watch the pest population decrease over time and reapply neem oil weekly until you see improvement.