Biopesticides

Biopesticides are the pesticides of biological origin or the biological control agents, which are used to control the weeds and pests; they are of 2 types bio herbicides and bio insecticides.

Bioherbicides

Chemical herbicides are persistent in nature and do not breakdown easily, they damage the crop plants themselves and encourage the growth of resistant weeds.

The biological control of weeds involves utilisation of biological agents such as insects fungi, bacteria, and parasitic plants etc., which suppress or kill the weedy plants without causing injury to other plants.

Examples of weed control by bio herbicides.

1) The first effective bioherbicide was a mycoherbicide phytophthora plamivora, which controls the growth of milk weed units in citrus orchards.

2) Growth of cacti in India was checked by the introduction of the natural herbivore cochineal insect cactoblastis cactorum.

3) Attempts to control water hyacinth in India were made by the application of alternaria eichhorniae.

4) Plant breeders have developed transgenic tomato and tobacco plants by genetic engineering by introducing the genes for herbicidal resistance into crop plants so that the new plants became herbicidal resistant. The herbicide kills the weeds selectively and the transgenic crop plants remain healthy.

Bio insecticides

The harmful insects and disease causing plants are controlled by the application of their natural parasites and predators.

1) Baculo virusis infect the larval stage of many harmful insects such as wasps and beetles but are harmful to non target organisms.

2) Bacteria Bacillus thuringensis contains an insecticidial crystal protein called thurioside, which is a stomach poison, and highly insect specific these toxins are known to be biodegradable and inactive against mammals and animals.

3) Aphids are controlled by the use of ladybugs or the praying mantis.

4) The fungus Beauveria bassiana is used to control potato beetle and codling moth.

Some commonly used biopesticides are:

• Nuclear poly hydrosis virus (NPV) - which is a dose of pathogenic virus. It is commercially available against the control of deadly pests such as bollworms of cotton.

• Commercial release of predators the Tricograma to control pests like pyrilla in sugarcane.

• Encouraging the population of beneficial insects like ladybird beetles and spiders - which eat away many pests.

• Use of natural insecticides such as neem (Azardactiva indica) based products like neem oil, neem cake, neem extract etc.

• Products like pyrethrum (from chrysanthamum) and nicotine (from nicotiana fabaccum) are also useful as biopesticides.

• Use of hormones or sterilants to interfere in the insect life cycle and bring about their control.

Additional Information

1) An insecticide from neem Azadrachta indica has been developed in the USA as a dust and spray.

2) A safe herbal pesticide has been developed from garlic and chillies in pune -maharashtra.

3) Scientists at CDRI in lucknow have developed biocide from the micro-organism Bacillus sphacricus which has been found to be effective in controlling the mosquito menace.

4) An effective insecticide has been developed from an extract of Annona sguamosa (custard apple).

5) Indian scientists have introduced weevils and fungal pathogen Alternaria eichhornae in West Godavari irrigation belts to control the growth of water hyacinth.

6) The overall loss caused by weeds in India has been estimated to be 27% of field crop production.