Author: Gugulotu Laxman
Division of Entomology, ICAR-Indian Agricultural Research Institute, New Delhi-110012
Corresponding author: laxmanagrico@gmail.com
Some plants contain components that are toxic to insects. When extracted from the plants and applied on infested crops, these components are called botanical pesticides or botanicals. The use of plant extracts to control pests is not new. Rotenone (Derris sp.), nicotine (tobacco), and pyrethrins (Chrysanthemum sp.) have been used widely both in small-scale subsistence farming as well as in commercial agriculture. Most botanical pesticides are contact, respiratory, or stomach poisons. Therefore, they are not very selective, but target a broad range of insects. This means that even beneficial organisms can be affected. Yet the toxicity of botanical pesticides is usually not very high and their negative effects on beneficial organisms can be significantly reduced by selective application. Furthermore, botanical pesticides are generally highly bio-degradable, so that they become inactive within hours or a few days. This reduces again the negative impact on beneficial organisms and they are relatively environmentally safe compared to chemical pesticides
Neem: Neem derived from the neem tree (Azadiracta indica) of arid tropical regions, contains sev-eral insecticidal compounds. The main active ingredient is azadiractin, which both deters and kills many species of caterpillars, thrips and whitefly. Both seeds and leaves can be used to prepare the neem solution. Neem seeds contain a higher amount of neem oil, but leaves are available all year. A neem solution looses its effectiveness within about 8 hours after preparation, and when exposed to direct sunlight.
Recommendation to farmers about preparation of neem pesticides: Pound 30 g neem kernels (that is the seed of which the seed coat has been removed) and mix it in 1 litre of water. Leave that overnight. The next morning, filter the solution through a fine cloth and use it immediately for spraying. It should not be further diluted.
Neem cake (ground neem seed or neem kernel powder) has also a considerable potential as a fertilizer and at the same time it will hinder nematode attacks of the crop roots (e.g. tomato). Put neem cake in the planting pit (200g per m2) and mix it with substrate. The neem cake will repel and even kill nematodes and other root pests. Insecticidal agents (azadirachtin) will be translocated to above-ground parts of the plant and help to get rid of pests there.
Pyrethrum: Pyrethrum is a daisy-like Chrysanthemum. Pyrethrins are insecticidal chemicals extracted from the dried pyrethrum flower. The flower heads are processed into a powder to make a dust. This dust can be used directly or infused into water to make a spray. Pyrethrins cause immediate paralysis to most insects. Low doses do not kill but have a knock down effect. Pyrethrins break down very quickly in sunlight so they should be stored in darkness.
Recommendation to farmers about preparation of Pyrethrum pesticides : Pyrethrum powder is made with dried ground flowers. Use pure or mix with a carrier such as talc, lime or diatomaceous earth and sprinkle over infested plants. To make liquid pyrethrum extract (mix 20g pyrethrum powder with 10 l water), add soap to make the substance more effective. Strain and apply immediately as a spray. For best effects this should be applied in the evening. Pyrethrum can also be extracted by alcohol.
Chillipepper: Chillies and capsicum pepper have both repellent and insecticidal effects.
Recommendations to farmers on preparation of chilli pesticides : To make the chilli extract grind 200 grams of chillies into a fine dust, boil it in 4 litres water, add another 4 litres of water and a few drops of liquid soap. This mixture can be sprayed against aphids, ants, small caterpillars and snails.
Garlic: Garlic has antifeedant (insect stop feeding), insecticidal, nematicidal and repellent properties. Garlic is reportedly effective against a wide range of insects at different stages in their life cycle (egg, larvae, adult). This includes ants, aphids, armyworms, diamondback moth, whitefly, wireworm and termites. Garlic is non-selective, has a broad-spectrum effect and can kill beneficial insects as well. Therefore, it should be used with caution.
Recommendations to farmers on preparation of garlic pesticides : To make the garlic extract, grind or chop 100 grams garlic into 0.5 litre water. Allow mixture to stand for 24 hours, add 0.5 litre of water and stir in liquid soap. Dilute at 1:20 with water and spray in the evening. To improve efficacy, chilli extract can be added.
Precautions to farmers regarding use of plant extracts :
- Despite being “natural” and widely used in agricultural systems, some botanicals may be dangerous for humans and they can be very toxic to natural enemies. Nicotine for example, derived from the tobacco plant, is one of the most toxic organic poisons for humans and other warm-blooded animals. Pyrethrins are not poisonous for humans and warm-blooded animals. However, human allergic reactions are common. It can cause rash, and breathing the dust can cause headaches and sickness.
- Before a new botanical pesticide is applied in a large scale, its effect on the ecosystem should be tested in a small field experiment. Do not just use botanical pesticides as a default option! First understand the ecosystem and how botanicals influence it
- Do not have direct skin contact with the crude extract during the process of preparation and application
- Contact with plant extracts should be avoided in the eyes
- Place the plant extract out of reach of children during storage
- Wear protective clothing (eyes, mouth, nose and skin) while applying the extract and wash your hands after handling the plant extract.
About Author / Additional Info:
Pursuing Ph D in Entomology in Indian Agricultural Research Institute