3. PESTICIDE FORMULATION
Formulation
Pesticides are rarely applied in their pure form because it would not be safe, convenient or
economic to apply them in that form. The pure form needs to be first formulated (processed) as
mixtures containing other ingredients that improve its properties of storage, handling and
application. Pesticide formulation thus refers to the processing of a toxic compound by any
method that will improve its properties of storage, handling, application, effectiveness and
safety. A formulated product simply means something that is processed and ready for use. For
example, dairy milk in its natural state is a liquid that cannot store long without going sour but
when processed and formulated as milk powder such as Everyday®, Amulya or Milkmaid, it can
be stored for long and is convenient for use. In the simplest sense, formulation means to put
certain ingredients together (using a formula) to make a product or commodity with enhanced
value.
Why pesticides have to be formulated?
At the chemical factories, synthetic pesticides come out in various forms: large crystals, lumps,
flakes, and as viscous oils. These are known as Technical Grade material (TC) or Active
Ingredient (A.I.). And they cannot be used in this highly concentrated form. Such products are
not yet processed are considered as unformulated pesticides. These highly concentrated materials
would neither be safe nor economic or convenient for application. It is not possible to get an
even distribution essential for effective pest control. Therefore, the technical grade materials
have to be processed into usable forms, usually called formulations, which can be distributed or
sold for application. During the process of formulation the concentrated TC or AI is diluted by
blending with “additives”.
How pesticides are formulated?
Since unformulated pesticides or pesticides in a raw form are highly concentrated, one of the
most important steps in the formulation process is to dilute the concentrated technical material. If
not diluted, it would neither be safe for handling nor fit (stable) for storage. It would not be
convenient for spraying. Dilution of technical material to produce a formulated pesticide can be
accomplished in several ways. Generally a formulated product has the following ingredients:
 Technical grade material (TC) or active ingredient (AI)
 Solvents
 Carriers
 Surface active agents
 Special additives
Active ingredient /Technical grade material
The TC or the active ingredient (AI) is the actual toxic component and therefore the most
important ingredient in a formulation.
Carriers
The term carrier is generally used to denote the inert solid ingredients used to dilute the technical
material, usually in dry formulations such as dusts, dispersible powders and granules. A typical
carrier is pyrophyllite, an inert clay.
Solvents
Solvents are liquid media in which the TC or AI are dissolved. The solvents may be miscible or
immiscible with water (milk is miscible with water whereas diesel oil is not). Those solvents not
miscible with water will require addition of another component known as the emulsifier or the
surfactant.
Surface active agents (surfactants)
These are agents that reduce the surface tension and increase the wetting power of water. Soaps
or detergents have these properties. The emulsifying agents or emulsifiers, wetting agents or
wetters, dispersing agents or dispersants, foaming agents and spreading agents all belong to the
group of surface active agents.
A solution of surface-active agents in water differs from pure water in several ways. It firstly
lowers the surface tension, enhances wetting power and dispersing properties.
How surface tension is lowered?
Surface-active agents have a characteristic structure which gives them unique properties. Their
chain-like molecules have a part which is attracted to water (hydrophilic) and is water soluble;
they also have a part that repulses water (hydrophobic) but is soluble only in organic solvents. In
a watery solution, these molecules collect at the surface while pushing their hydrophobic tailportion out of the water into the air. If the surfactant concentration is high, these molecules will
cover the entire surface and lower the surface tension. Increasing the surface area of such a
solution is much easier than increasing that of pure water. In other words its surface tension is
much lowered.
AIR
WATER SURFACE
WATER
HYDROPHOBIC
HYDROPHILIC
Figure:
The portion of the surfactant molecule that does not like (hydrophobic) water
forces itself to the surface of a water solution thereby changing the characteristics
of the surface.
How the wetting power is enhanced?
The hydrophobic tails at the surface of the solution are the hydrocarbon groups in the surfactant
molecules. Owing to their presence, the surface of the solution resembles the surface of a
hydrocarbon or oil. Because the surface of a leaf is often covered with a layer of wax to
minimize transpiration, the wetting of a waxy leaf cuticle is easier to achieve with oil than with
pure water. This is the reason why a surfactant solution, with its oil-like surface, wets a leaf
better than water does. Adding a surface-active agent to formulation thus improves its wetting
power in solution.
Reduction of surface tension and improvement of wetting power both play an important role in
while spraying chemicals. They have a profound influence on the size of the spray droplets and
on the spreading, retention and run-off of the spray liquid on the target surface.
Leaf surface
Figure: Wetting of leaf surface when wetting agents are not used
Figure: Wetting of leaf surface after wetting agent is used
How the dispersion properties are enhanced?
A third characteristic of a surfactant solution is its dispersing property, which is related to the
same phenomenon that causes the improved wetting power. Because water and oil are
immiscible, when the two are mixed by stirring and shaking, the droplets of oil quickly form a
layer on the top. When an emulsifier or a surfactant is added, the molecules of the surfactant will
collect around the droplets of oil. The hydrophobic tails of these molecules then penetrate into
the oil droplets, while their hydrophobic heads remain in the water portion of the solution. The
congregation of surfactant molecules, in the so-called interface between water and oil cause a
more-or-less stable situation in which the oil droplets remain dispersed in the water, giving the
water a milky appearance. This is called dispersion because the oil remains as microscopic sized
droplets.
Water
oil
Figure:Drawing of oil droplet in a surfactant solution
Special additives
These additives are used in a formulation or added separately into spray tank while preparing to
spray.
Examples: stabilisers – used to prevent the deactivation of a.i.; synergists – increases pesticide
activity; wetters – to increase wetting power; oils – to reduce evaporation loss, to reduce wash
off; assist penetration; defoamers – to prevent excessive foaming; thickeners – prevent formation
of small droplets and therefore reduce evaporation and enhances viscocity, prevents runoff;
colouring agents – reduce the possibility of accidents.
Pesticide formulation codes
The considerable increase in the worldwide manufacture of pesticide called for a harmonized
(uniform) system for the designation of formulation. In 1978, a world-wide coding system was
prepared under the co-ordination of the International Association of Pesticide Manufacturers
(GIFAP); the system was last revised in 1989. The coding system consists of 2 letters for each
formulation type:
Group 1: Concentrates for dilution with water
EC – Emulsifiable Concentrate
SL - Soluble Concentrate
SC – Suspendable concentrate
SP - Soluble Powder
WP - Wettable Powder
WG/SG – Water dispersible Granules/Soluble Granules
Group 2: Formulations to be applied undiluted
GR – Granules
DP – Dustable Powder (dusts)
UL – Ultra low volume (ULV) liquid
Group 3: Miscellaneous formulations for special purpose
RB – Ready to use Bait
Definition of terms: Dispersion, emulsion, solution, suspension
If we add oil into water, they do not mix well but instead form two separate layers. The oil which
is light forms the upper layer. Such liquids are said to be immiscible liquids. On the other hand,
when two liquids mix well (e.g. alcohol and water) they are said to be miscible. The molecules of
the two liquids are well dispersed (spread out or scattered) and forms a stable situation and such
a mixture of well dispersed liquid is known as dispersion. The dispersion of liquid in a liquid
(e.g. oil-in-water) is called emulsion. Fine globules of an organic solvent containing the
technical ingredient are dispersed in water.
In a solution, no separate droplets can be formed because the dissolving process is complete at
the molecular level.
A suspension is the dispersion of a wettable powder (WP) or a water-dispersible powder in a
liquid.
EC – Emulsifiable Concentrate
An emulsifiable concentrate is a solution of an active ingredient in a non-water miscible solvent.
It contains an emulsifier to help the concentrate mix with water upon slight agitation and form an
emulsion. It contains usually 15 to 50 percent of active ingredient that has to be diluted with
water to form a solution in a spray tank.
WP- Wettable Powder
This type of formulation is also termed water dispersible powder, and is applied as a suspension
after its dispersion in water. A wettable powder is a mixture of the active ingredient with
powders and certain chemicals to improve its solution in water. Wettable powders are essentially
dusts containing 25 to 50 percent of active ingredient and certain other chemicals, which have to
be diluted in water to form a solution for spraying.
GR- Granules
Granules are defined as free flowing, ready-to-use, solid product of a defined granule size.
Granular formulations are usually made by spraying a liquid concentrate of the technical grade
material onto small pellets of some absorptive material. Uniform chips of broken bricks and
coarse grains of sand are commonly used.
This type of formulation can be used without application equipment and virtually any time of the
day, since they can be applied even in strong winds without the problem of drift. They can also
be drilled into the soil at planting time to protect roots against insects or to improve uptake of a
systemic pesticide by the roots.
A disadvantage of the granular formulation is the high cost of manufacturing, handling, storing
and transporting materials of low concentration.
DP- Dustable Powder
This type of formulation is a ready-to-use, free-flowing powder, generally with a low
concentration of active ingredient, and suitable for dusting. Dustable powders are prepared by
mixing and grinding the technical grade material together with an inert diluent such as
pyrophyllite clay. If the technical grade material is a liquid, it has to be absorbed by the diluent
before mixing and grinding.
Ready-to-use baits (RB)
Baits are formulations designed to attract and to be eaten by the target pest. They consist of a
mixture of food, attractive to the pest, and a pesticide. The concentration of active ingredients in
these baits is less than 5 per cent. They are used to control rats and mice. Ready-to-use bait that
is available in Bhutan contains Bromadialone as rodenticide. Zinc phosphide is also used in baits
to control rats and mice. This rodenticide is however, not available as a ready-to-use bait but
farmers have to prepare the bait themselves and mix the rodenticide with it.
Special baits
A form of baiting used in Bhutan involves the addition of protein hydrolysate or Di-ammonium
phosphate that attracts the Chinese Citrus Fly, a major pest of mandarins, to a spray solution of
Malathion or Chlorpyrifos. The use of this bait makes it possible to treat only a small part of the
tree to achieve effective fly control instead of treating the entire tree with a cover spray.