Neem Oil and Insects
Neem oil has a bitter taste and a pungent smell. In its original form, this oil does not mix with water. So surfactants are used to make it soluble in water. Such a solution works as a bio-pesticide for organic farming. However, you should not expect immediate results, as it works gradually.
Neem oil has many ingredients and the action of each and every ingredient is not known. Various insect species react differently to this oil, and it is also observed that neem oil does not cause harm to beneficial insects. It is believed that the oil affects only chewing and sucking insects.
As per experts, the ingredients of neem oil can block the action of hormones in insects. As the oil enters the system of the insects, their hormones stop working properly. As a result, the insects stop their activities, like eating, mating, and laying eggs. Even if eggs are laid, they don't hatch. This inaction affects the very survival of the insects.
It is also observed that the smell of neem oil wards off insects, and deters them from eating the crops. In general, pesticides tend to wash away with rain, or degenerate with sunlight. Strong ones, which can withstand these factors, may stay for a longer period.
Neem oil also disintegrates easily, but plants absorb and retain it in their tissues. In such cases, the smell of the oil deters insects. It may also happen that they take a few bites and leave the plant.
The presence of trace amounts of neem oil cannot cause any harm to human beings, as it is consumed in small amounts for medicinal purposes. It is also believed that, like white oil and olive oil, neem oil too creates a coating over the insects, when sprayed on them. This coating suffocates them to death.
How to Use Neem Oil as an Insecticide
For this purpose, the oil should be diluted with water. Four teaspoons of neem oil is sufficient for a gallon of water. This solution can be sprayed on the foliage or can be used as a soil drench (one liter for one square meter of soil).
Surfactants are used to enhance the efficiency of neem oil as an insecticide. Usually, liquid dishwashing soap is used for this purpose. A tablespoon of dishwashing soap is sufficient for a gallon of water.
The best time for application of neem oil insecticide, is early morning, late afternoon, or evening. This is to avoid harm to the beneficial insects, which are active during daytime only. Once the application gets dry, it cannot harm those insects, as they do not feed on plants, like the harmful ones.
In case of heavy infestation, apply neem oil pesticides, once in every seven days. If you want to prevent pests, use it once in every 14 days. Neem oil can control pests, like aphids, moth larvae, whitefly, Japanese beetles, scales, and spider mites.
This oil is known to kill mites, and also act as a fungicide, against black spot, leaf spot, anthracnose, rust, and mildew. You can replace your chemical pesticides with neem oil for your houseplants or crops.