Classification of pesticides

From this figure, we can see that China, The USA and Argentina account for 70% of world pesticide use in agriculture. These countries consume about 2.4 billion kg of active ingredients per year. China now uses half of pesticides worldwide. And rice is the major crop to consume pesticides in China. China has also become the largest pesticide producer and exporter in the world.

Pesticides can be classified in a number of ways, such as target organisms, origin and chemical structure. Based on target organisms, pesticides can be classified into Insecticides, Herbicides,Fungicides, Bactericides and so on. Insecticides control insects, and herbicides control weeds. Insecticides are the most widely used pesticide in the world. So pesticides are not only used in agriculture, but also used at a lower concentration in homes and on pets to get rid of ants, flies,fleas and cockroaches. In according to origin, pesticides can be classified into chemical pesticides and bio-pesticides. Chemical pesticides are synthesized chemicals and Bio-pesticides are microorganisms or naturally occurring substances such as insect sex pheromones. If classified based on chemical structure, pesticides can be grouped into organochlorines, organophosphates, carbamates, and so on.

Organochlorine pesticides were widely used as insecticides Due to their capability of persisting in the environment and accumulating to high levels, Use of organochlorine pesticides has been banned for decades in many countries including Taiwan. Now, The most commonly used insecticides are the organophosphates, carbamates and pyrethroids. However, organophosphates and carbamates are toxic to the nervous system. Certain organophosphorus pesticides have been banned or restricted for use on crops. Hazards of Pesticides are classified by their acute toxicity. We will talk about it later. Pesticides can also be classified by their physical state such as solubility, volatility and partition coefficient. The partition coefficient measures how hydrophilic or hydrophobic a pesticide is.

Pesticides with high partition coefficients are mainly distributed to hydrophobic areas which could have a potential for bio-accumulation. Pesticides work by interfering with an essential biological mechanism in the pests, such as inhibition of acetylcholinesterase and modulation of ion channels. For example, organophosphates and carbamates are potent acetylcholinesterase inhibitors which lead to acetylcholine accumulation and neurotoxicity. Mode of Action is another way to classify pesticides. Systemic pesticides, in general, are high water soluble, which allows them to be taken up by plant roots or leaves and disperse through the whole plant. Some pesticides only have local-systemic activity. They can penetrate leaf tissues and form a reservoir of active ingredient within the leaf.

Contact pesticides are applied to surfaces of plants which control pests as a result of direct contact.