Agricultural Chemicals

Pesticide DefinitionAgricultural chemicals: Pesticides

Economic poisons: control, kill, repel pests.

In other words, pesticides are those chemical, biological or physical agents used to kill, control or repel unwanted animal or plant pests.

Definitions and TermsCategories:FungicidesHerbicidesInsecticidesRodenticidesFumigants

Key PointsUnique pollutants in that they are designed to kill.Ideally, objective is to be highly selective.Destroy target without effects to non-target organisms.Realistically, benefit vs. risk to health and environmental quality are weighed.

Pesticide FormulationsActive ingredient.Formulations: solid or liquid.Adjuvants: adhesives, surfactant spreaders and emulsifiers.Solvents: water, xylene or oil.

HerbicidesUsed to control weeds, fairly specific.Widespread usage (half of pesticides).Typically inhibit plant specific enzymesLow mammalian, fish, insect, bird toxicities.Continual usage however leads to environmental contamination.

FungicidesUsed to prevent crop loss and health effects from toxins released by fungi.e.g., chlorothalonilrelatively nontoxicDithiocarbamatese.g., mancozebrelatively nontoxic but hydrolyze to produce carcinogens such as ethylenethiourea (ETU)

RodenticidesUsed to prevent losses in grain and other food storage facilities.Generally restricted use onlye.g., warfarin, an anticoagulantlack of blood clotting leads to bleeding to death (LD50: 3.0 mg/kg)

FumigantsUsed to protect stored products (e.g., grains) and kill nematodes.Hazardous due to potential for inhalation exposure (restricted use only).e.g., methyl bromideLD50: 0.06 mg/L (inhalation, rat)Effects include respiratory distress, cardiac arrest, and CNS effects

Biocontrol PesticidesUses natural mechanisms for combat.Parasites (Aphytis lepidosaphes, wasp)Predators (Neoseliulus califirnicus, spider mite)Attractants (pheromones)Nontoxic to humans.

Definitions and TermsKey PointsPesticide FormulationsFungicides

RodenticidesFumigants

Biocontrol Pesticides