Bill Sutherland from Growing Edge Technologies discusses neem oil and how it can form an important part of your indoor garden pest control program.
WHAT IS NEEM OIL?
Neem oil is a natural product derived from the seeds of the neem tree (Azadirachta indica). The neem tree is native to tropical and semi-tropical regions of South Asia but also grows in the Middle East and some parts of Africa. Most of the widespread cultivation and use of neem is in India, where it has been used for over two thousand years as a medicinal treatment for a plethora of ailments and disorders. The neem tree is an evergreen, which grows to around 60 ft (18 m) and produces white aromatic flowers followed by a small fruit that looks much like a large olive. Inside the fruit lies the payload; one large seed from which the oil is extracted by either cold pressing or solvent extraction. A by-product of neem oil extraction is a solid dried product called â€˜neem cakeâ€™, which can be used as an organic fertilizer as well as a good method of controlling soil-dwelling pests. Here we will focus on the properties, uses and advantages of neem oil when used as a natural pest control agent for your homegrown fruits and flowers.
Please note: Neem oil products are not currently registered for use as a pesticide in Canada.
What does neem oil do?
This may sound disappointing, but it needs to be said: neem is not an insecticide that kills on contact, and it has a low instant â€˜knock downâ€™ effect. However, it is still very effective! Unlike other chemical insecticides, neem oil gets into an insectâ€™s body after the ingestion of neem coated plant material and gets to work within a few hours. The predominant active component in neem oil is called azadirachtin, and once in a pestâ€™s body it directly affects the hormonal system, more so than the digestive or nervous system. The way in which azadirachtin targets the hormonal system means that insects are far less likely to develop resistance in future generations. As well as azadirachtin, other liminoid compounds present in natural neem oil (nimbin, salanin, gedunin, azadirone, melandriol and more) play a significant collaborative role in deterring feeding and reducing pest populations.
Biological Effects of Neem Oil on Insects
Historical use and recent research studies show that a broad range of phytophagous (plant eating) pest insects are affected and can be controlled by neem oil, these include:
- Orthoptera: grasshoppers, katydids, crickets etc.
- Coleoptera: wide range of beetles/weevils
- Hemiptera: leafhoppers, aphids, psyllids & some scale insects
- Lepidoptera: cutworms, borers & caterpillars
- Thysanoptera: thrips
- Diptera: Sciarid fly, fruit fly, buffalo/blow & march fly
- Heteroptera: sucking bugs â€“ Green veggie bug, spotted fruit bug etc.
- Others: nematodes, snails, and also some fungi and pathogenic viruses
1. Insect Growth Regulation
Neem oil is unique in nature since it works on juvenile hormones. The insect larva feeds and when it grows, it sheds its old skin and continues growing. This molting phenomenon, also know as ecdysis, is predominantly governed by the enzyme ecdysone. When the ingested neem, or more specifically azadirachtin,Â enters into the body of larva, the activity of ecdysone is suppressed. This causes molting failure and results in the larva not developing to the next life stage, and ultimately dying. If only a small amount of neem-coated foliage is ingested, and the concentration of azadirachtin is insufficient to cause molting failure, the larva will manage to enter a short-lived prepupal stage where it will die. In some instances, where the concentration of azadirachtin is still less, the adult emerging from the pupa will be malformed and sterile, without any capacity for reproduction.
2. Feeding Deterrent
One of most important properties of neem oil is feeding deterrence. Most insects are permanently hungry during their larval stages, particularly when they are mobile on the leaf surface. An insectâ€™s maxillary gland is responsible for initiating feeding. When these glands give a signal, peristalsis in the alimentary canal is increased, which makes the larva feel hungry, and makes it start eating. When a leaf is treated with neem oil, the presence of the liminoids azadirachtin, salanin and melandriol produces an anti-peristaltic wave in an insectâ€™s alimentary canal, producing something similar to a vomiting sensation combined with a reduced ability to swallow. Because of this sensation, an insect will avoid feeding on neem-treated leaf surfaces.
3. Oviposition Deterrent
Another way in which neem oil reduces pests is by not allowing the females to deposit eggs. This property is known as oviposition deterrence, and quickly thwarts the pest population growth. Interestingly, studies by Knapp & Kashenge (Insect Sci. Applic.2003) on spider mites, and Singh & Singh (Phytoparasitica, 1998) on fruit flies have shown that natural neem oil formulations are more effective as oviposition deterrents and insect mortality than azadirachtin concentrates alone. Results from Knappâ€™s & Kashengeâ€™s study showed that azadirachtin does not seem to play a major role in the control of spider mites. Although, azadirachtin is an important component of neem oil, the other less studied ingredients seem to have a positive synergistic effect when it comes to effecting the behavior, effectiveness and mortality of plant pests.
Neem Oilâ€™s Effect on Non-Target Species and Beneficial Insects
One of the problems with the use of chemical pesticides has been their impact on non-target species, particularly when used outdoors. Often they have proved harmful to other beneficial species present in the ecosystem. Neem oil products have proved to be remarkably benign to insects such as adult bees and butterflies that pollinate crops and trees, ladybugs that consume aphids, and wasps that act as parasites on various crop pests. As mentioned above, neem oil has to be ingested to be effective. Those insects that feed on plant tissues, therefore, easily succumb. However natural enemies that feed only on other insects, and bees and butterflies that feed on nectar rarely come in contact with significant concentrations of neem oil to cause themselves harm.
Neem Oilâ€™s Other Benefits as a Foliar Spray
Beside its insecticidal and nematicidal properties, neem oil is also a promising agent for the control of viral and fungal plant diseases. Neem oil in combination with paraffin oil has been shown to greatly reduce disease incidences of the yellow vein mosaic virus of okra and legumes, and leaf curl of chili, all of which can cause enormous losses. Neem oil has also been shown to reduce transmission of the tobacco mosaic virus in greenhouse vegetable crops of pepper, cucumber and tomato.
Neem oil has been demonstrated to suppress fungal activity. Fungi are constantly evolving enemies of growers and some can reach epidemic proportions. Neem oil has been shown to protect seeds against fungal diseases while in storage, and be beneficial as a preventative spray for fungal leaf diseases such as powdery and downy mildew.
Neem oil also contains some key nutrients that make it a good foliar fertilizer. A typical good quality neem oil product found in your local grow store will contain the following plant nutrients:
- Total Nitrogen 1.20% by mass
- Phosphorus as P 0.07% by mass
- Potassium as K 0.01% by mass
- Magnesium as Mg 0.03% by mass
- Copper as Cu 10 ppm
- Magnesium, as Mn 0.40 ppm
- Zinc as Zn 20.00 ppm
- Iron content 14.00 ppm
So, not only will regular spraying of neem oil onto your plant foliage control pests, it will also help prevent diseases and act as a foliage fertilizer! Amazing stuff.
How to Use Natural Cold-Pressed Neem Oil:
Like most of the vegetable oils, natural cold-pressed Neem oil is non-soluble in water and has to be made soluble with suitable emulsifiers before spraying. Some commonly available emulsifiers that can be used are liquid soaps, eco-friendly detergents, surfactants, wetting agents, soap nut powder, and many other organic emulsifiers.
- Collect together your equipment.
- To make 10 liters of spray-able neem, pour 1 liter of water into a container, add 10â€“15 ml of liquid soap, or a suitable emulsifier, and agitate well until the soap/emulsifiers completely dissolve.
- To this solution add 50 ml of neem oil and agitate well until a pale yellowish white emulsion is formed.
- Add this prepared emulsion to 9 liters of water in a bucket and stir thoroughly. The neem solution is now ready for spraying.
Spraying should be done within 8 hours of mixing, using a suitable sprayer. This solution can be used as a foliar spray on crops, and also can be sprayed on the surface of growing media for effective action against root pests.
It is recommended to repeat the spraying 5 times at intervals of 7 to 10 days. Spraying should be undertaken during periods of low light intensity; outdoors or in greenhouses this should be in the early morning or late in the evening. If you grow under lights, raise them high and consider turning a few off to reduce light intensity before spraying.
- To make 10 liters of drench-able neem. Add 1 liter of water to a container. Add 20â€“30 ml of liquid soap, or suitable emulsifier, and agitate well until the soap/emulsifiers completely dissolve.
- To this solution add 250â€“350 ml of neem oil and agitate well until a pale yellowish white emulsion is formed.
- Add this prepared emulsion to 9 liters of water in a bucket and stir thoroughly. The neem solution is now ready to pour onto the growing medium. Apply enough for a small amount of run-off to occur.
Please Note: Drenching potting soil with neem will adversely affect the beneficial biology of the rhizosphere. If you need to drench the root zone with neem, a follow up application with a good quality actively aerated compost tea will help to re-inoculate the beneficial bacteria, fungi and protozoa.
Neem Oilâ€™s Effect on Plants
Neem oil not only coats the plant foliage after spraying, it is actually absorbed into the leaf material and can be transported around the plant systemically. Neemâ€™s liminoid compounds (mainly azadirachtin) can be taken up by the roots after root zone applications, thereby reaching leaf and stem material throughout the whole plant. This reinforces the anti-feeding deterrent properties or neem oil, which makes the whole plant rather unappealing to invading pests.
Due to this persistence in the plant, neem oil products should not be used on plants that are approaching maturity. As a general rule, avoid spraying or soil drenching neem oil on plants that have five weeks left before harvest. As mentioned above, neem products have been used topically and ingested for medicinal use by humans for thousands of years and are completely non-toxic. However, neem has a very bitter taste that can, if used too late in a plantâ€™s life cycle, be passed into the developing consumable produce.
Summary of the Advantages of Neem Oil
- Broad spectrum of activity
- No known insecticide resistance mechanisms
- Compatible with many other insecticides and fungicides
- New mode of action with possible multiple sites of attack
- Low use rates
- Compatible with other biological control agents for Integrated Pest Management programs.
- Not persistent in the environment
- Minimal impact on non-target organisms
- Formulation flexibility
- Application flexibility â€” can be sprayed or drenched