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Neem Oil: Garden Pest And Disease Fighter

One of the most reliable organic pesticides out there is neem oil. Neem oil products are often the first we mention in the pest control portions of past Epic Gardening pieces. That’s because neem oil works! When it comes to a natural pesticide, neem is something you want to have at hand. 

Neem oil comes from the seeds and fruit of the neem tree and has multiple uses in a garden. Not only is growing a neem tree making way for lovely sights and smells, you have access to an excellent nitrogen booster for soil in the form of neem seed. And you can even make your own neem oil.

But thankfully you won’t even have to do that to apply neem oil spray to plants. This plant-based pesticide is widespread and available in most big box stores, online outlets, and even small local nurseries. Safe for use all the way up to harvest day, it’s an effective pest control treatment for over 200 types of insect pests as well as a biofungicide. We consider it a staple here, and highly recommend that you try it out in your gardening efforts, too!

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What Is Neem Oil?

Neem oil comes from neem trees (Azadirachta indica), a highly popular cultivar across the world’s tropical climates. The seeds and fruits of the neem plant are pressed to get the vegetable oil we call neem oil. Neem seed oil is yellow, brown, or even a vibrant red. It has a pungent odor that smells like a mix of peanuts and garlic, with a slightly sulfuric tinge. Often neem products are a combination of neem oil and a surfactant, which subsumes the oil and activates it, making it ready for use on plants. That being said, neem doesn’t mix well with water. The fatty acids in the oil called triglycerides have insecticidal properties, bactericidal, antiviral, and fungicidal properties, which makes it highly useful to organic gardeners everywhere. Especially because it kills aphids, mealybugs, mites, thrips, and whiteflies on contact. 

Clarified hydrophobic extract of neem oil is a derivative that comes from neem oil extract treated with alcohol. Clarified hydrophobic neem oil is useful for fighting insect pests with soft bodies, like aphids and mealybugs, and also for combatting fungal diseases like mildew and rust.

How Does Neem Kill Insects?

Azadirachtin
This complex structure is responsible for neem oil’s powerful pesticidal properties. source

The chemical Azadirachtin is the main active ingredient in neem oil products. In combination with other active compounds, Azadirachtin promotes an anti-feeding behavior in soft-bodied insects. It’s also a hormone disruptor of detrimental insects, preventing normal growth and development. Neem oil is effective in all stages of insect growth. It kills eggs, larvae, nymphs, and adults alike. That’s why neem oil sprays are used in other countries to control fleas on cats. This is also a testament to how safe and effective neem oil is.

How Does Neem Treat Disease?

While neem oil has significant insecticidal properties, it also treats bacterial and fungal diseases. As well as bacterial and fungal disease, gardeners can use neem oil to prevent viral disease vectors as well. It does not truly cure any diseases, but it limits their proliferation and reduces the likelihood of further spread. In fungi, neem oil prevents the germination of spores and also keeps spores from penetrating leaf tissue. It’s specifically useful for treating powdery mildew in this regard.

Neem oil is particularly effective in preventing fire blight, which is a highly infectious bacterial disease that infects fruit trees in the Rosaceae family. Because neem oil insecticide kills pests, it helps prevent the spread of viruses they may be carrying. While actual anti-viral properties are in question in peer-reviewed studies, it’s easy to see how an integrated pest management strategy that includes neem oil can assist in controlling diseases on ornamental plants, indoor plants, or garden plants in general. 

Benefits Of Using Neem Oil

Neem oil
Neem oil is a very useful addition to the gardener’s toolkit. Source: bnpositive

Neem oil pesticides are not only effective, but they’re also generally recognized to be non-toxic to only slightly toxic by the Environmental Protection Agency, and the National Pesticide Information Center. It does not harm birds, mammals, bees, and plants. You can use neem oil to control insects like Japanese beetles, other beetle larvae, leafhoppers, spider mites, and aphids. As you spray to kill pests, you’ll also shield the entire plant from the harmful effects of some diseases.  

It also has a residual effect of helping earthworms, which means it won’t harm your soil. That’s because neem oil is made from neem cake – the solid mass of seeds and fruit from neem trees pressed to extract the oils. Neem cake is used to amend and condition soils and pack a punch of nitrogen that many amendments can’t compare to. While other pesticides might have a toxic effect on beneficial insects and soil content, even when sprayed in a small area, neem seed oil will protect your plants at a foliar and soil surface level without damage to your garden friends.

Drawbacks Of Using Neem Oil

Neem leaves
More than 200 types of insects, some diseases, and more are treated by this tree. Source: Tatters

While using pure neem oil has plenty of benefits, if it’s used improperly, it can be detrimental to plants and beneficial insects. As with any other pesticides, you’ll want to wear protective gear when you apply the neem oil insecticide because the concentrated form can irritate skin and sensitive areas, like the eyes and lungs. If you’re using wettable powders, pour the liquid in carefully to prevent blowback and inhalation of neem into the lungs. Children are also at risk because they are more sensitive to neem oil than adults. It goes without saying that even though any irritation can be minimal, keep it away from pets and children. It’s also slightly harmful to fish and amphibians. Using neem oil on aquatic plants where fish and amphibians are present is not recommended. 

If you use neem oil properly, there should be no worries about irritation of skin or sensitive areas. Likewise, proper use ensures no harm is done to beneficial insect populations, birds, or the ecology of the surrounding environment.

How to Use Neem Oil

Neem fruit
Inside the neem fruit are the seeds from which neem oil is pressed. Source: Starr

Always check the product label carefully before using neem oil. Put on gloves and protective eyewear if you know you risk making contact while applying neem oil. Cold-pressed neem oil needs to be mixed in a spray bottle. Combine a drop or two with a small amount of liquid you’re going to test on your plant. Add commercial insecticidal soap to create a neem oil mixture. The soap acts as an emulsifier that helps neem oil work more effectively. Note the oil’s effectiveness will break down within 8 hours, so don’t make more than you need. 

If you’re spraying an indoor plant, take it to an area where neem oil can’t irritate children or pets. Spray the neem oil on a small area to ensure it won’t burn your plants. Always spray at dusk or just before the sun rises. After spraying a small section, wait 24 hours to determine that neem oil pesticide hasn’t burned your plants. If the spray hasn’t caused any discoloration or singing, you know you’re good to go. Formulate a larger batch to spray the whole plant.

Then mist the plant leaves with your neem oil insecticide from the bottom leaves up. Ensure the undersides of leaves are coated as this is where most of the insect pests feed on plants. When you spray, don’t drench the plants. Instead, allow a light mist to coat the leaves. Then follow up with another light application in 7 to 10 days. It will take time for the neem oil pesticide to build up effectiveness, so reapplication is key. 

You can use pure neem oil to combat fungi and bacteria that cause diseases on your vegetables and fruit too. Spray trees outside of their blooming season, every two weeks until bud break. Then hold off, and resume after the flowers drop. While the spray creates inhospitable conditions for fungi such as powdery mildew, it also does so for bacteria and insects that may be vectors for disease. On fruit trees, aphids and mites are often an issue, and using organic neem oil preventatively will have a multi-layer benefit in this way.

Another awesome non-toxic way to keep insects and other pests from feeding on your plants is to soak the soil. Formulate organic neem oil pesticides in the same manner as you would for a foliar spray. Then, pour 2 to 3 cups of the neem oil mixture around the base of each plant in your garden. You can repeat this process every 2 to 3 weeks until the insects have left the area or the disease symptoms lessen. It will take at least 2 weeks for the effectiveness of neem oil to work on the garden soil. Simply apply the soil soak around each plant every three weeks during the planting season as a preventative measure to control pests and disease before they take hold. Sometimes, adding a little neem seed meal around your plants can act similarly!

Neem seed meal
The byproduct of neem oil, neem seed meal, is a fertilizer and pest reducer. Source: Lorin Nielsen

Furthermore, you can use the natural insecticide neem oil to treat plants that might have bugs that overwinter in your garden. Because some insects lay eggs on leaves that fall and remain on the earth until the next season, a neem oil spray can help control moth larvae and bugs like spider mites that lay eggs that wait out the cold season to return when the weather warms. 

One note: if your plant is already stressed, that’s not the best time to apply straight neem oil. Even though it’s organic and relatively non-toxic, a plant that is already sensitive due to stress from insects or disease can experience more stress from neem oil. This goes for soil soaks and spraying neem oil.  

A Word On Pollinators

Many people discuss the risk that neem oil can present to large hives of bees and populations of other pollinators. While many pesticides do pose a threat to pollinators, neem oil insecticide doesn’t if it’s used correctly. We as gardeners should indeed look out for pollinators, and do what we can to ensure they are safe. We can still use neem oil as substantial insect control while ensuring pollinators are not adversely affected.

One way to do this is to ensure the plants aren’t soaked with neem oil in the garden. Light mists will dry within 45 minutes to an hour because that’s how long neem oil’s moisture lasts when mixed with water. Spray before the time pollinators come out to allow it drying time, or apply in the evening once your pollinators have retreated to hives and homes. 

In a soil drench, the half-life of neem oil extends from 3 days up to 22 days. That’s why it’s best to wait three weeks for a reapplied soil soak. The times that pollinators are usually out working their way through your garden are generally after sunrise, and before sunset. By spraying before or after those times, you’re using an effective insecticide that rids plants of pests and doesn’t harm pollinators. Butterflies, ladybugs, and lacewings don’t feed on plant matter, so as long as the misting of neem oil you’ve applied to your plants has evaporated, they’re in the clear.

Frequently Asked Questions

Azadirachta indica
Azadirachta indica is a gorgeous tree in its own right. Source: lalithamba

Q: What is neem oil used for?

A: Neem oil is a highly effective insecticide. It’s also an effective fungicide and bactericide. Residually, it controls viral outbreaks too and improves soil fertility. 

Q: Is neem oil harmful to humans?

A: Not really, but it can irritate skin and sensitive areas of the human body. Children are more susceptible to slight irritation. 

Q: Can I apply neem oil directly on skin?

A: While it won’t seriously hurt you, it can irritate the skin when undiluted. Wear gloves when applying and avoid skin contact. There are some diluted forms used in skin creams or ointments, but with these, check with your physician before use.

Q: Is neem oil a fungicide?

A: While it’s not as potent as copper fungicides, it has shown effectiveness as a preventative fungicide.