A pesticide: ‘Any chemical or biological preparation used to control or modify the effects of injurious organisms’. I.e: Not all methods of chemical control involve spraying insecticides that disrupt signalling between neurons in a pest insect’s nervous system. Some chemical methods serve to disrupt growth and moulting processes, repel or attract the pest to a particular area (away from the crop), disrupt mating or navigation to the crop plants, or even to call in natural enemies (such as predators and parasitoids) of the pest insect.
Simple chemical control is the spraying of artificial chemical which disrupts signalling pathways in insects, killing them upon contact, ingestion or fumigation. Insecticides can be classified depending on their mode of action: acetylcholinesterase inhibitors (carbamates, organophosphates), GABA antagonists (cyclodienes, lindanes, DDT), Sodium channel blockers (pyrethrins and pyrethroids) and nicotinic acetylchloine receptor agonists (neonicotinoids). The source of all these pesticides ioriginated naturally occurring plant defense compounds (for example permethrin from Chrysanthemum) which have been synthesized into much higher concentrations for spraying.
Chemical control is used to reduce the levels of damage that are high enough (above an economic threshold) to financially justify pest control (or ‘management’) methods. Pests can be weeds, molluscs, fungi, nematodes or insects, and can attack agricultural and horticultural crops, forests and even humans as disease vectors. Another method of control of pests is to use natural enemies, as in biological control.
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