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.
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.
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
||Full sun, Part shade
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
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.
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.
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.
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.