Spraying a blooming fruit tree.

Neem Oil: Organic Pesticide and Fungicide

Excerpted from: How To Use Neem Oil
Excerpted from: How To Use Neem Oil On Plants

  Neem oil is a plant-based pesticide and fungicide that’s been used for decades to control pests in gardens and on crops.

Neem oil is an organic solution used as a pesticide against insects, mites, or fungi bothering your plants. It will not harm humans or animals, and it's safe even for most wildlife since its insecticidal properties are targeted to specific pests that damage garden plants.

  What Is Neem Oil?

Neem tree.
Neem tree.

Neem oil is a naturally occurring pesticide found in seeds from the neem tree (Azadirachta indica). It is yellow to brown, has a bitter taste, and a garlic/sulfur smell. It has been used for hundreds of years to control pests and diseases.

Components of neem oil can be found in many products today. These include toothpaste, cosmetics, soaps, and pet shampoos. Neem oil is a mixture of components.

Azadirachtin is the most active component for repelling and killing pests and can be extracted from neem oil. The portion left over is called clarified hydrophobic neem oil.

  How Does Neem Oil Work?

Neem oil is made of many components. Azadirachtin is the most active. It reduces insect feeding and acts as a repellent. It also interferes with insect hormone systems, making it harder for insects to grow and lay eggs.

Azadirachtin can also repel and reduce the feeding of nematodes. Other components of neem oil kill insects by hindering their ability to feed. However, the exact role of every component is not known.

Microbes and light break down the pesticide in soil, water and on plants. The half-life of azadirachtin in soil ranges from 3-44 days. In water, the half-life ranges from 48 minutes to 4 days. It also rapidly breaks down on plant leaves; the half-life is 1-2.5 days. The remaining components of neem oil are broken down by microbes in most soil and water environments.

  How To Use Neem Oil

Neem Tree
Azadirachta indica
Height 50-75 feet
Width 50-75 feet
Zone 10-12
Sun Full sun, Part shade
Soil 3 years
Flower color White
Bloom period Seasonal

Spray neem oil on foliage in the morning or evening when beneficial bugs are dormant and not feeding or pollinating. Avoid using the spray in the middle of the day when the sun and heat could burn the sprayed foliage. You can use neem oil throughout the planting season.

Neem oil is effective at any time during a season because it affects insects during all phases of their development.

If you have a bad infestation, apply the neem oil solution to the stems, leaves (including the undersides), and soil. Microbes and light quickly break down the pesticide in soil, water, and leaves.1

What does neem oil do to bugs? According to the EPA, neem oil interferes with the normal life cycle of insects, including feeding, molting, mating, and egg-laying.

Neem oil controls hundreds of pests, including whitefly, aphids, Japanese beetles, moth larvae, scale, and spider mites. Neem oil is also listed as a miticide because it kills mites, which are not insects but are related to spiders and ticks.

Sprays containing clarified hydrophobic neem oil extract are also used as fungicides against rust, black spot, mildew, leaf spot, scab, anthracnose, blight, and botrytis. Neem oil does not harm birds or beneficial insects and soil-loving creatures, such as bees, butterflies, lady beetles, and earthworms.

Please remember, neem oil is good at limiting the spread of fungal diseases in plants but it can not cure a plant that is already infected by a fungal disease.

  Common Mistakes When Using Neem Oil

Do NOT use Medically Preferred neem oil combined with an emulsifying agent like soap. This will damage your plants. Only use Agricultural Grade neem oil that comes in water soluble form.

No NOT use neem oil when the sun is high or the temperature is hot as the spray will damage the leaves and the neem oil rapidly breaks down in sunlight. Using either in early morning or late evening will allow the plant to absorb the neem oil.

Neem oil is not as effective when used on plants that are already infected. Neem oil only works 1-3 days before it is broken down by sunlight and microbes. You should use neem oil as a preventative - before plants are infected - at least twice a month.

  Neem Oil's Toxicity

  What happens to neem oil when it enters the human body?

Clarified hydrophobic neem oil (without azadirachtin) is made of fatty acids and glycerides. These substances are commonly found in food. When they enter the body, they are broken down, used for energy, and incorporated into cells.

In one study, scientists injected insects with azadirachtin. They found 90% of the dose in the insects' feces within 7 hours. The remaining portion lingered in the insects' bodies for 24 days after the injection.

  Can neem oil affect birds, fish, or other wildlife?

Neem oil is practically non-toxic to birds, mammals, bees and plants. Neem oil is slightly toxic to fish and other aquatic organisms. Azadirachtin, a component of neem oil, is moderately toxic to fish and other aquatic animals. It is important to remember that insects must eat the treated plant to be killed. Therefore, bees and other pollinators are not likely to be harmed.

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