Biocontrol agents and biofertilisers

The essentials

Biocontrol means using biological methods, rather than chemical pesticides, to control plant diseases and pests. Chemical pesticides are toxic to humans and animals and pollute soil and water, whereas biocontrol works with natural predation and is more eco-friendly. Organic farmers aim to keep pests at manageable levels through a balanced ecosystem rather than eliminating them.

Examples of biocontrol agents:

• Ladybird beetles (red with black spots) control aphids; dragonflies control mosquitoes.
• Bacillus thuringiensis (Bt): its spores are sprayed on plants; when eaten by insect larvae, the toxin is released in the gut and kills caterpillars such as those of butterflies, without harming other insects. Bt toxin genes have also been introduced into plants.
• Trichoderma: free-living fungi common in root ecosystems; effective against several plant pathogens.
• Baculoviruses, especially the genus Nucleopolyhedrovirus: attack insects and arthropods; they are species-specific, narrow-spectrum and have no negative effect on plants, mammals, birds, fish or non-target insects, making them suitable for integrated pest management (IPM).

Biofertilisers are organisms that enrich the nutrient quality of soil. The main sources are bacteria, fungi and cyanobacteria.

• Rhizobium forms root nodules in leguminous plants and fixes atmospheric nitrogen symbiotically.
• Azospirillum and Azotobacter are free-living soil bacteria that fix nitrogen.
• Mycorrhiza: symbiosis of fungi (for example Glomus) with plant roots; the fungus absorbs phosphorus from soil for the plant and gives resistance to root pathogens, tolerance to salinity and drought, and better growth.
• Cyanobacteria such as Anabaena, Nostoc and Oscillatoria fix nitrogen in aquatic and terrestrial environments; they are important in paddy fields and add organic matter to soil.

Common mistakes

• Trichoderma is a fungus, not a bacterium or virus.
• Mycorrhizal fungi mainly help phosphorus uptake, not nitrogen fixation.