Biocontrol and biofertilisers

Chemical pesticides and fertilisers harm people, animals and the environment. Microbes and other living things can do the same jobs more safely.

Biocontrol is the use of biological methods to control plant diseases and pests. Organic farmers do not try to wipe out pests completely; they keep them at a manageable level with a balanced, living system, because many insects in a field are useful or harmless, and killing everything also kills the pests' natural enemies.

Some biocontrol agents:

• Predators: the ladybird beetle eats aphids; dragonflies eat mosquitoes.
• Bacillus thuringiensis (Bt): its dried spores are mixed with water and sprayed on plants. When caterpillars (such as butterfly larvae) eat them, a toxin is released in their gut and kills them, while other insects are left unharmed. Scientists have also put the Bt toxin genes into plants, which then make the toxin themselves: Bt-cotton is an example.
• The fungus Trichoderma lives freely around roots and controls several plant pathogens.
• Baculoviruses attack insects and other arthropods. Those of the genus Nucleopolyhedrovirus are species-specific: they attack only the target pest and are harmless to plants, mammals, birds, fish and other insects. That makes them ideal for integrated pest management (IPM), especially in sensitive areas.

Biofertilisers are organisms that enrich the soil with nutrients:

• Bacteria: Rhizobium lives in root nodules of legumes such as peas and beans, and fixes atmospheric nitrogen into a form the plant can use. Azospirillum and Azotobacter fix nitrogen while living freely in the soil.
• Fungi: many fungi form a partnership with plant roots called mycorrhiza; for example, Glomus. The fungus absorbs phosphorus from the soil and passes it to the plant, which also becomes more resistant to root pathogens and drought.
• Cyanobacteria (blue-green algae), such as Anabaena, Nostoc and Oscillatoria, fix nitrogen in water and soil. They are important biofertilisers in paddy fields, and they also add organic matter to the soil.