Pesticides: Classification, Formulations and Mode of Action
Pesticides: Classification, Formulations and Mode of Action
This domain tests how pesticides are grouped, how formulations behave in the spray tank and how mode of action guides choice and resistance management.
Core rules
- By target: insecticides, fungicides, herbicides, rodenticides, nematicides and molluscicides.
- By formulation: EC (emulsifiable concentrate), WP (wettable powder), SC (suspension concentrate), WG (water-dispersible granule), dust and granule. EC forms an emulsion; WP forms a suspension; SC is a ready-to-mix suspension.
- By toxicity: WHO classes Ia, Ib, II, III and U; lower LD50 means higher toxicity.
- Mode-of-action examples: organophosphates inhibit acetylcholinesterase; pyrethroids act on sodium channels; neonicotinoids act on nicotinic acetylcholine receptors; glyphosate inhibits EPSPS; atrazine blocks photosystem II.
- Use adjuvants only when the label allows; check compatibility before tank mixing.
Worked example
A label gives 2 mL product per litre and the spray volume is 200 L/ha. Reasoning: 2 mL/L x 200 L = 400 mL product per hectare. For a 16 L knapsack, the dose is 2 mL x 16 = 32 mL. Do not add extra product to compensate for poor coverage; calibrate the sprayer instead.
Traps
Confusing formulation with active ingredient, mixing EC products in hard water without checking, and repeating one mode of action are common errors.
Key distinction
An EC needs an emulsifier and forms a milky emulsion; a WP forms a suspension and needs agitation.