Pesticide formulations and application
Why pesticides are formulated, the common formulation codes, adjuvants, sprayers and nozzles, droplet size and drift, and how to calibrate a sprayer.
On this page
A pesticide's active ingredient is rarely sold on its own. Most active ingredients are solids or oils that do not mix with water, are toxic to handle in pure form, or break down quickly in sunlight. Formulation turns them into products that can be measured, mixed, sprayed or spread safely and effectively. Then the product has to reach the target, the underside of a leaf, the inside of a cotton boll or the soil around a seed, without drifting onto neighbours, waterways or the operator.
Formulation types, application equipment and calibration are standard exam topics in plant protection, entomology and agricultural engineering, and they matter more for results than many farmers realise.
What is in a formulated product
- Active ingredient (a.i.): the substance that controls the pest.
- Inert or co-formulants: solvents, carriers, emulsifiers, dispersants, wetting agents, antifoams, stabilisers and preservatives that make the product work and keep it stable.
The label gives the concentration as grams per litre (g/L) for liquids or per cent by weight for solids. Many formulations also carry a two-letter CropLife International code.
Common formulation types
| Code | Formulation | Description |
|---|---|---|
| EC | emulsifiable concentrate | a.i. dissolved in solvent with emulsifiers; forms a milky emulsion in water |
| SC | suspension concentrate | fine solid particles suspended in water; low dust, low solvent |
| CS | capsule suspension | a.i. inside microcapsules; slower release, often safer to handle |
| EW, ME | emulsion in water, microemulsion | oil droplets in water; less solvent than EC |
| SL | soluble concentrate | a.i. dissolved in water, such as glyphosate salts |
| WP | wettable powder | fine powder suspended in water; dusty to handle |
| WG (WDG) | water-dispersible granules | granules that disperse into a suspension; less dust than WP |
| SP, SG | water-soluble powder or granules | dissolve completely |
| OD | oil dispersion | solid particles in oil; good leaf uptake |
| GR | granules | applied dry to soil or water, as in rice paddies |
| DP | dustable powder | applied dry; drifts badly, now rare |
| FS, WS | seed-treatment flowable or powder | coat seeds |
| RB | bait | a.i. mixed with food attractive to the pest |
| UL | ultra-low-volume liquid | applied undiluted in very small volumes |
Fumigants, such as phosphine-generating tablets for stored grain, act as gases.
Trends favour formulations with less solvent and dust (SC, WG, CS, OD) for operator safety and the environment.
Adjuvants
Adjuvants are added to the tank or built into the product to improve performance:
- Surfactants (wetters and spreaders) lower surface tension so droplets spread on waxy leaves.
- Stickers help deposits resist rain.
- Penetrants, such as crop oils and methylated seed oils, increase uptake of some herbicides.
- Drift-reduction agents increase droplet size.
- Buffers and water conditioners correct pH or hard water, which can reduce the activity of some products.
Only use adjuvants that the label permits; the wrong one can injure the crop.
Application equipment
- Hydraulic sprayers: knapsack sprayers, tractor-mounted and self-propelled boom sprayers. Pressure forces liquid through nozzles:
- flat-fan nozzles give an even band, standard for boom spraying of herbicides;
- hollow-cone nozzles give fine droplets and good coverage, used for insecticides and fungicides on foliage;
- air-induction nozzles produce coarse, air-filled droplets that drift much less.
- Air-assisted sprayers (mist blowers, air-blast orchard sprayers) carry droplets into dense canopies with a stream of air.
- Controlled droplet applicators (spinning discs) make droplets of uniform size, used in ultra-low-volume spraying, for example against locusts.
- Drones and aircraft for large areas or hard-to-reach crops, subject to strict rules in most countries.
- Granule applicators, seed treaters, soil injectors, trunk injection and chemigation through irrigation systems.
Droplet size and drift
Smaller droplets cover a target more thoroughly but evaporate and drift. Drift wastes product, damages neighbouring crops and contaminates water and homes. To reduce it:
- Choose nozzles giving coarser droplets where coverage allows, especially for herbicides.
- Spray when wind is light and steady, not in calm, hot conditions with temperature inversions.
- Keep boom height low and pressure within the nozzle's range.
- Leave buffer zones near water and sensitive areas.
Calibrating a sprayer
The label dose is useless unless the sprayer delivers a known volume per hectare.
Calibrating sprayers and working out product
Boom sprayer. Nozzles are 0.5 m apart, each delivers 0.8 L/min (measured by collecting its output for one minute), and the tractor travels at 6 km/h.
- Application rate = 0.8 × 600 ÷ (6 × 0.5) = 480 ÷ 3 = 160 L/ha.
- With a 600 L tank, each fill covers 600 ÷ 160 = 3.75 ha.
- If the label calls for 1.5 L of product per hectare, each tank needs 1.5 × 3.75 = 5.6 L of product.
Knapsack sprayer. An operator sprays a measured 100 m2 plot with water at normal walking speed and uses 4 L.
- Rate = 4 L per 100 m2 = 4 × 100 = 400 L/ha.
- A 16 L knapsack covers 16 ÷ 400 = 0.04 ha (400 m2), so a product used at 1.0 L/ha needs 40 mL per knapsack.
Granules. A soil insecticide is recommended at 1.0 kg a.i./ha as a 5 per cent granule (GR): 1.0 ÷ 0.05 = 20 kg of granules per hectare.
Recalibrate whenever nozzles, pressure, speed or the operator change; worn nozzles can deliver 10 to 20 per cent more than new ones.
Key points
- Formulation makes the active ingredient safe, stable and usable; the label gives concentration and a two-letter code.
- Common types: EC, SC, CS, EW, SL, WP, WG, SP, OD, GR, FS, baits and fumigants; low-dust, low-solvent types are replacing older ones.
- Adjuvants improve spreading, sticking, uptake or drift control; use only label-approved ones.
- Flat-fan nozzles for herbicides, hollow-cone for foliar insecticides and fungicides, air-induction to reduce drift; air-assisted sprayers for tree crops.
- Smaller droplets cover better but drift more.
- Boom sprayer rate (L/ha) = nozzle output × 600 ÷ (speed × spacing).
What the exams ask
- School-leaving and entrance papers: types of formulations with examples, and spraying equipment.
- Degree and research-fellowship entrances: formulation codes and properties, adjuvants, nozzle types, droplet size and drift, and calibration calculations.
- Agricultural engineering and professional examinations: sprayer design and calibration, drift management, ULV and drone application, and dose calculations for different formulations.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Why does an EC turn milky in water?
The active ingredient is dissolved in a solvent with emulsifiers. In water, the solvent breaks into tiny droplets dispersed through the water, which scatter light and look milky.
Can I mix two products in one tank?
Only if both labels allow it and they are physically and chemically compatible. A small jar test shows whether they separate, curdle or form sludge; the usual mixing order is water-dispersible solids first, then liquids, then soluble products and adjuvants.
Does a finer spray always work better?
No. It covers better in calm conditions, but more of it drifts or evaporates before reaching the target, and wind can carry it far. Choose the coarsest droplets that still give adequate coverage.
Sources
- Matthews, G. A., Bateman, R. and Miller, P. Pesticide Application Methods, 4th edition. Wiley-Blackwell, 2014.
- CropLife International. Catalogue of Pesticide Formulation Types and International Coding System, Technical Monograph 2, 7th edition, 2017.
- FAO. Guidelines on Good Practice for Ground Application of Pesticides. FAO, Rome, 2001.
- ASABE. Spray Nozzle Classification by Droplet Spectra (ANSI/ASABE S572.3). American Society of Agricultural and Biological Engineers, 2020.
- Knowles, D. A. (ed.) Chemistry and Technology of Agrochemical Formulations. Kluwer Academic Publishers, 1998.
More in entomology and crop protection
Discussion
Questions, corrections and notes from readers on this article. Every comment is checked before it appears: keep it on the topic, and do not share phone numbers, links or contact details.