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Pesticide: Types and Classification


Types of pesticides

Different Types of Formulations
were adopted   internationally.  There  
are   common   abbreviations in pesticide formula. Here are
some of the most common  kinds  of 
pesticide  formulations  available 
to  give  a better understanding of what they are:

Pesticide can be in terms as; Active ingredient (a.i.), Emulsion, Fumigant, Impregnates, Pheromones, Phytotoxicity, Solution and Suspension

Dusts are made up of a finely ground mixture of low concentration of active ingredient (10% or less by weight) combined with very fine and dry inert carrier made from clay, talc, chalk, nut hulls or volcanic ash in powdered form.

Dusts are intended for dry use and should never be mixed with water. The percentage of active ingredient in a dust is generally quite low. Dusts are commonly used for interior wall void and perimeter treatments (seed dressing), as  well as  for  crop-dusting.

Dust formula  can  be  used  in  cracks,  crevices,  spot  treatment  to control insects such as cockroaches, insects ingest poisonous dusts during grooming or absorb the dust through their outer body covering, also can be used to control lice, fleas and other parasites on pets and livestock. In case of concentrates a high percentage of active ingredients mixed with few inert carriers before  diluted  with  water  or  solvent  and  applying  as  spray. There are many advantages of dusts; it is most ready use with no mixing, effective where moisture from a spray might cause damage, required simple equipment and effective in  hard-to- reach indoor areas. In contrast there are some disadvantages of dust pesticides such as; easily drift off – target during application, residue easily moved off-target by air movement or water, may irritate eyes, nose, throat and skin, will no stick to surfaces as well as liquids, dampness can cause clogging and lumping, and difficult to get an even distribution of pesticide particles on the target surfaces [24].

Are hard, dry particles made up
of porous materials and active ingredient? Granular formulations are similar to
dust formulations, except granular particles are larger and heavier. The coarse
particles are made from materials such as clay, corncobs, or walnut shells
[24]. The active ingredient either  coats
 the 
outside  of  the 
granules  or  is 
absorbed  into them. The amount of
active ingredient is relatively low, usually ranging from 1 to 15 percent by
weight. The percentage of active ingredient in a granule formulation is higher
than that of a dust but lower than that of an EC. Granules are usually safer to
apply than dusts or ECs.

Granular formulations are used
most often for soil treatments. Granular pesticides are most often used to
apply chemicals to the soil to control weeds, nematodes, and insects living in
the soil, or for absorption into plants through the roots. Granular
formulations are sometimes applied by airplane or helicopter to minimize drift
or to penetrate dense vegetation. Once applied, granules release the active
ingredient slowly. Some granules require soil moisture to release the active
ingredient. Granular formulations also 
are  used  to 
control  larval  mosquitoes 
and other aquatic pests. Granules are used in agricultural, structural,
ornamental, turf, aquatic, right-of-way, and public health (biting insect)
pest-control operations.

Its advantages; ready to use—no
mixing, drift hazard is low, and particles settle quickly, little hazard to
applicator-no spray, little dust, weight carries the formulation through
foliage to soil or water target, simple application equipment needed, such as
seeders or fertilizer spreaders and may break down more slowly than WPs or ECs
because of a slow-release coating.

Aerosols

Sold in cans and contain one or more active ingredients and a solvent under pressure. Aerosols pesticides are sold most often for home and garden use, not for agricultural use. The percentage of active ingredient in aerosols is usually very low.

 Aerosols

Its disadvantages; often
difficult to calibrate equipment and apply uniformly, will not stick to foliage
or other uneven surfaces, may  need  to 
be  incorporated  into 
soil  or  planting 
medium, may  need  moisture 
to  activate  pesticide, 
may  be  hazardous to 
non-target  species,  especially 
waterfowl  and  other 
birds that mistakenly feed on the seed-like granules and may not be
effective under drought conditions; the active ingredient is not released in
sufficient quantity to control the pest.

Most pellet formulations are very similar to granular formulations; the terms are used interchangeably. In a pellet formulation, however, all the particles are the same weight and shape. The uniformity of the particles allows use with precision application equipment. A few fumigants are formulated as pellets. However, these are clearly labeled as fumigants. Do not confuse them with non-fumigant pellets.

Various types of insect
repellents are available in aerosol and lotion formulations. People apply these
to their skin or clothing or to plant foliage to repel biting and nuisance
insects. You can mix other types of repellents with water and spray them onto
ornamental plants and agricultural crops to prevent damage from deer, dogs, and
other animals.

Are sold in cans and contain one
or more active ingredients and a solvent under pressure. Aerosols pesticides
are sold most often for home and garden use, not for agricultural use. The
percentage of active ingredient in aerosols is usually very low. One of the
main advantages of aerosols is that they are convenient and easy to use. Many
aerosols are used for killing pests on contact, or for time-released control of
flying pests.

What is a Formulation?

Pesticides are available in various “formulations”. A formulation is simply the form of a specific product that you use. Some insecticide formulations include dusts, gels, granules, liquids, aerosols, wettable powders, concentrates, and pre-mixed solutions.

There are two types of aerosol
formulations-the ready-to-use type commonly available in pressurized sealed
containers and those products used in electrical or gasoline-powered aerosol
generators that release the formulation as a “smoke” or “fog.”

Ready-to-use aerosols: These
formulations are usually small, self-contained units that release the pesticide
when the nozzle valve is triggered. The pesticide is driven through a fine
opening by an inert gas under pressure, creating fine droplets.

These products are used in
greenhouses, in small areas inside buildings, or  in 
localized  outdoor  areas. 
Commercial models, which hold five to 5 pounds of pesticide, are usually
prefillable.

Its advantages; ready to use,
portable, easily stored, convenient way to buy a small amount of a pesticide
and retain potency over fairly long time and its disadvantages are; practical
for only very limited uses, risk of inhalation injury, hazardous if punctured
(overheated, or used near an open flame) and difficult to confine to target
site or pest [24].

Wettable powders are dry, finely
ground formulations that look like dusts. They appear similar to a dust but
contain additional wetting and dispersing agents so that water may be added for
maximum effectiveness. Wettable powders are also more highly concentrated than
dusts to contain more active ingredient. The particles do not dissolve in
water, they usually must be mixed with water for application as a spray. A few
products, however, may be applied either as a dust or as a wettable powder—the
choice is left to the applicator. Wettable powders contain 5 to 95 percent
active ingredient by weight; usually 50 percent or more. Wettable powder
formulations do not form a true solution when water is added, they settle out
quickly  unless  constantly 
agitated  to  keep 
them  suspended so frequent
agitation of the spray tank is required to keep the formulation in suspension.

They can be used for most pest
problems and in most types of spray equipment where agitation is possible.
Wettable powders have excellent residual activity. Because of their physical
properties, most of the pesticide remains on the surface of treated porous
materials such as concrete, plaster, and untreated wood. In such cases, only
the water penetrates the material.

Its  advantages 
are;  easy  to 
store,  transport,  handle, 
less likely than ECs and other petroleum-based pesticides to cause
unwanted harm to treated plants, animals, and surfaces, easily measured and
mixed and less skin and eye absorption than ECs and other liquid formulations
[24].

Its disadvantages are; inhalation
hazard to applicator while measuring and mixing the concentrated powder,
requires good and constant agitation (usually mechanical) in the spray tank and
quickly settles out if the agitator is turned off, abrasive to many types of
pumps and nozzles, causing them to wear out quickly, difficult to mix in very
hard, alkaline water, often clog nozzles and screens and residues may be
visible on treated surfaces.

Emulsion: An emulsion occurs when
one liquid is dispersed (as droplets) in another liquid. Each liquid retains
its original identity. Some degree of agitation generally is required to keep
the emulsion from separating. Emulsions usually have a milky appearance. The
active ingredient is dissolved in an oil-based solvent. When the  product is 
mixed with water, an  emulsion
(oil  in 
water)  is  formed. 
An  emulsifying  agent 
(often  called an emulsifier)
formulated into the product helps prevent the emulsion from separating.
Familiarity with these terms and processes leads  to 
a  greater  understanding and  appreciation of the advantages and
disadvantages of many commonly used pesticide formulations.

Emulsifiable concentrates are
liquid formulations where the active ingredient is dissolved in oil and an
emulsifier is added so that the formulation may be mixed with water for
spraying. ECs are among the most widely used formulations, along with wettable
powders. ECs typically contain two to six pounds of active ingredient per
gallon. Unlike wettable powders, ECs require very little agitation and are easy
to handle.

They are adaptable to many types
of application equipment, from small, portable sprayers to hydraulic sprayers,
low-volume ground sprayers, mist blowers, and low-volume aircraft sprayers.
Its  advantages  are; 
relatively  easy  to 
handle,  transport,  and store, little agitation required—will not
settle out or separate when equipment is running, not abrasive, will not plug
screens or  nozzles and  little visible residue on  treated surfaces. And its disadvantages are;
high a.i. concentration makes it easy to overdose or under dose through mixing
or calibration errors, may  cause  damage 
to  desirable  plants 
(phytotoxicity), easily absorbed through skin of humans or animals
(solvents may cause rubber or plastic hoses, gaskets, and pump parts and surfaces
to deteriorate), may cause pitting or discoloration of painted finishes,
flammable—should be used and stored away from heat or open flame and may be
corrosive.

An  invert 
emulsion  contains  a 
water- soluble pesticide dispersed in an oil carrier. Invert emulsions
require a  special kind of  emulsifier that allows the pesticide to  be 
mixed with a  large volume of  petroleum-based carrier, usually fuel oil.
Invert emulsions aid in reducing drift. With other formulations,  some 
spray  drift  results 
when  water  droplets begin to evaporate before reaching
target surfaces; as a result, the droplets become very small and light. Because
oil evaporates more slowly than water, invert emulsion droplets shrink less;
therefore, more pesticide reaches the target. The oil helps to reduce runoff
and improves rain resistance. It also serves as a sticker-spreader by improving
surface coverage and absorption. Because droplets are relatively large and
heavy, it is difficult to get thorough coverage on the undersides of foliage.
Invert emulsions are most commonly used along rights-of-way where drift to
susceptible non-target plants or sensitive areas can be a problem.

Are liquid formulations where the
active ingredient is dissolved in oil so that the formulation mixed with oil
for spraying. OCs typically contains two to six pounds of active ingredient per
gallon. OCs require very little agitation and are easy to handle.

Are   liquid  
formulations where the active ingredient is dissolved in gasoline so
that the formulation mixed gasoline for spraying. GCs typically contain two to
six pounds of active ingredient per gallon. It require very little agitation
and are easy to handle.

Are dry formulations similar to
wettable powders, but the difference is that when added to water a soluble
powder will dissolve completely and form a genuine solution (whereas a wettable
powder does not). Some agitation may be 
required to  dissolve the soluble
powder initially, but once a solution, agitation is not needed. The amount of
active ingredient in soluble powders ranges from 15 to 95 percent by weight; it
usually is more than 50 percent. The percentage of active ingredient in a
soluble powder is high compared to ECs and 
WPs,  and  there 
are  not  currently many  SP 
formulations available.

Soluble powders have all the
advantages of wettable powders and 
none  of  the 
disadvantages, except  the  inhalation hazard during mixing. Few
pesticides are available in this formulation because few active ingredients are
readily soluble in water.

Water-soluble packets reduce the
mixing and handling hazards of some highly toxic pesticides. Manufacturers  package 
precise  amounts  of 
wettable  powder or soluble powder
formulations in a special type of plastic bag. When you drop these bags into a
filled spray tank, they dissolve and release their contents to mix with the
water. There are no risks of inhaling or contacting the undiluted pesticide as
long as you do not open the packets. Once mixed with water, pesticides packaged
in water-soluble packets are no safer than other tank mixtures.

Tracking Powders: Special dusts
known as tracking powders are used for rodent and insect monitoring and
control. For rodent control, the tracking powder consists of finely ground dust
combined with a stomach poison. Rodents walk through the dust, pick it up on
their feet and fur, and ingest it when they clean themselves. Tracking powders
are useful when bait acceptance is poor because of an abundant, readily
available food supply. Non- toxic powders, such as talc or flour, often are
used to monitor and track the activity of rodents in buildings.

Dry flowables can also known as
water- dispersible granules. Are very similar to granules in appearance, and
behave in the same way as wettable powders except instead of being dust-like,
they are formulated as small, easily measured granules. Water-dispersible
granules must be mixed with water to be applied. Once in water, the granules
break apart into fine particles similar to wettable powders. The formulation
requires constant agitation to keep it suspended in water. Dry flowables have
several advantages over WPs because of their shape: they can be easily “poured”
and measured just like liquid, and are safer to use because very little dust is
released into the air when they are mixed and measured. Dry flowables contain
very high percentages of active ingredient.

Dry flowables contain very high
percentages of active ingredient. The percentage of active ingredient is often
as much as 90 percent by weight. Water-dispersible granules share many of the
same advantages and disadvantages of wettable powders, except they are more
easily measured and mixed. Because of low dust, they cause less inhalation
hazard to the applicator during handling. The main advantages over WPs because
of their shape: they can be easily “poured” and measured just like liquid, and
are safer to use because very little dust is released into the air when they
are mixed and measured [24].

Are made with active ingredients
that  cannot  be 
dissolved  completely  in 
water  or  oil, 
so  the active ingredient is
ground up and suspended in a liquid with other 
suspending  agents.  The 
formulation  is  then 
ready  to mix with water for
application. Flowables will not clog spray nozzles, and require only moderate
agitation. A flowable or liquid formulation combines many of the
characteristics of emulsifiable concentrates and wettable powders.
Manufacturers use these formulations when the active ingredient is a solid that
does not dissolve in either water or oil. The active ingredient, impregnated on
a substance such as clay, is ground to a very fine powder. The powder is then
suspended in a small amount of liquid. The resulting liquid product is quite
thick. Flowables and liquids share many of the features of emulsifiable
concentrates, and  they  have 
similar  disadvantages. They  require 
moderate agitation to keep them in suspension and leave visible
residues, similar to those of wettable powders.

Flowables/liquids are  easy 
to  handle  and 
apply.  Because they are liquids,
they are subject to spilling and splashing. They contain solid particles, so
they contribute to abrasive wear of nozzles 
and  pumps.  Flowable 
and  liquid  suspensions 
settle out in their containers. Always shake them thoroughly before
pouring and mixing. Because flowable and liquid formulations tend to settle,
manufacturers package them in containers of five gallons or less to make
remixing easier.

Solution: A solution results when
a substance is dissolved in a liquid. The components of a true solution cannot
be mechanically separated. Once mixed, a true solution does not require
agitation to keep its various parts from settling. Solutions are frequently
transparent.

Are liquids in their original
state and are fully soluble in water and any other solvent. Solutions that are
prepared the right way will not leave unsightly residues or clog spray nozzles.
Some pesticide active ingredients dissolve readily in  a 
liquid carrier such as water or a petroleum-based solvent. When mixed
with the carrier, they form a solution that does not settle out or separate.
Formulations of these pesticides usually contain the active ingredient, the
carrier, and one or more other ingredients. Solutions may be used in any type
of sprayer, indoors or outdoors.

Low- concentrate formulations are
ready to use and require no further dilution 
before  application.  They 
consist  of  a 
small  amount of active ingredient
(often 1 percent or less per unit volume) dissolved in an organic solvent. They
are especially useful for structural and institutional pests and for household
use. Major disadvantages of low-concentrate formulations include limited
availability and high cost per unit of active ingredient. Many organic solvents
are harmful to foliage, so they often cannot be used as plant sprays.

These concentrates may approach
100 percent active ingredient. They are designed to be used as is or to be
diluted with only small quantities of a specified carrier and are used at rates
of no more than a half-gallon per acre. These special-purpose formulations are
used mostly in outdoor applications, such as in agricultural, forestry,
ornamental, and mosquito- control programs. Ultra-low Volume (ULV) advantages
are; relatively easy to handle, transport, and store, remain in solution;
little  agitation required, not  abrasive to 
equipment, will  not  plug 
screens and  nozzles, leave
little  visible residue on treated
surfaces. And its disadvantages; difficult to keep pesticide on target—high
drift hazard, specialized equipment required, easily absorbed through skin of
humans or animals, solvents may cause rubber or plastic hoses, gaskets, and
pump parts and  surfaces to  deteriorate, calibration and  application must be done very carefully
because of the high concentration of active ingredient.


Suspension is  a  mixture of 
finely divided, solid particles dispersed in a liquid. The solid particles
do not dissolve in the liquid, and the mixture must be agitated to keep the
particles evenly distributed. Most suspensions will have a cloudy, murky
appearance. The label directs the user to shake well before using. Such
products also form suspensions when mixed with water for application as a
spray. Explicit label information describes the need for sufficient agitation
to keep the solid particles of the product dispersed in the spray tank.

An increasing number of
insecticides and rodenticides are being formulated as liquid baits. Liquid
rodenticides are mixed with water and placed in bait stations designed for
these products. They have two major benefits. Liquid rodenticides are effective
in controlling rodents, especially rats, in areas where they cannot find water.
They are also effective in areas of poor sanitation where ready availability of
food renders traditional baits 
ineffective. Liquid  insecticide
baits  are  used primarily by the structural pest control
industry for controlling ants and, to a lesser extent, cockroaches. They are
packaged as ready-to-use, sugar-based liquids placed inside bait stations.

Liquid insecticide ant baits have
a number of advantages. They are very effective against certain species of
sugar-feeding ants. These ants typically accept and transfer liquid baits into
the ant colonies. However, some ants will not feed on liquid baits. Liquid
baits also must be frequently replaced.

Are food-like substances mixed
with a pesticide specifically designed to attract and be eaten by insects or
other pests and eventually poison them to death. Baits are commonly used for
rodent control, including mice and rats. However, baits are also used to
control roaches, ants, flies, and other insects. Bait formulations can be used
indoors or outdoors. When compared to ECs or other formulations, the percentage
of active ingredient in bait is low [24]. A bait formulation is an active
ingredient mixed with food or another attractive substance. Are food-like
substances mixed with a pesticide specifically designed to attract and be eaten
by insects or other pests and eventually poison them to death. Baits are
commonly used for rodent control vertebrate pests such as mice and rats.
However, baits are also used to control such as rodents, other mammals, and
birds. Bait formulations can be used indoors or outdoors. Indoor to control
ants, roaches, flies, other insects, and rodents. Outdoors, they sometimes are
used to control snails, slugs, and insects such as ants and termites. When
compared to ECs or other formulations, the percentage of active ingredient in
bait is low. Its advantages are ready to use, entire area need not be covered,
because pest goes to bait and controls pests that move in and out of an area.
Its disadvantages are can be attractive to children and pets, may kill  domestic 
animals  and  non-target 
wildlife  outdoors,  pest may prefer the crop or other food to the
bait, dead vertebrate pests may cause odor problems, other animals may be
poisoned as a result of feeding on the poisoned pests and if baits are not
removed when the pesticide becomes ineffective, they may serve as a food supply
for the target pest or other pests.

Pastes,  Gels, 
and  Other  Injectable 
Baits:  Pastes  and gels are mainly used in the pest-control
industry for ants and cockroaches. Insecticides formulated as pastes and gels
are now the primary formulations used in cockroach control. They are designed
to be injected or placed as either a bead or dot inside small cracks and
crevices of building elements where insects tend to hide or travel. Two basic
types of tools are used to apply pastes and gels—syringes and bait guns. The
applicator forces the bait out of the tip of the device by applying pressure to
a plunger or trigger.

Its advantages are; they are odorless,
produce no vapors, have low human toxicity, and last for long periods;
applicator exposure is minimal, hidden placements minimize human and pet
exposure, very accurate in their placement and dosage and easily placed in  insect harborage for  maximum effectiveness. Its disadvantages; can
become contaminated from exposure to other pesticides and cleaning products,
when exposed to high temperatures, gels can run and drip, may stain porous
surfaces and repeated applications can cause an unsightly buildup of bait.

Are a  new kind of formulation in which the active
ingredient is held in a very small capsule (Microencapsulated). Manufacturers
cover liquid or dry pesticide particles in a plastic coating to produce a
microencapsulated formulation. These capsules are then suspended in a liquid.
This formulation of  suspended capsules
is  then mixed with water and maybe
applied with a sprayer. After spraying, the plastic coating breaks down and
slowly releases the active ingredient. Microencapsulated materials  have 
several  advantages;  highly toxic materials are safer for
applicators to mix and apply, Encapsulated pesticides are  safe and 
easy to  use, delayed or slow
release of the active ingredient prolongs its effectiveness, allowing for  fewer 
and  less  precisely timed  applications, the pesticide volatilizes
slowly; less is lost from the application site, allowing for greater
effectiveness and these formulations often reduce injury to plants.
Microencapsulated materials, however, pose a special hazard to bees, may pose a
threat to bees when they carry the capsules back to their hive; foraging bees
may carry microencapsulated materials back to their hives because they are
about the same size as pollen grains. As the capsules break  down, 
they  release  the 
pesticide, poisoning the  adults
and brood. Breakdown of the microencapsulated materials to release the
pesticide sometimes depends on weather conditions. Under certain conditions,
the microencapsulated materials may break down more slowly than expected. This
could leave higher residues of pesticide active ingredient in treated areas
beyond normal restricted-entry or harvest intervals with the potential to  injure 
fieldworkers.  For  this 
reason,  regulations  require long restricted-entry intervals for
some microencapsulated formulations [24].

Formulators may impregnate
(saturate) fertilizers and other materials with a pesticide. Such materials
must  be 
handled as  pesticides and  their 
use  must  follow 
all pesticide laws, regulations and safety and environmental
requirements. Some materials are impregnated in ways that allow the pesticides
to evaporate over time so the vapors provide control of nearby pests. These
types of pesticide impregnated products include pet collars, livestock ear
tags, adhesive tapes, and plastic pest strips. Some paints and wood finishes
have pesticides incorporated into them to kill insects or retard fungal growth.

Formulations  for  
smoke   or   fog  
generators:   These aerosol
formulations are not under pressure. They are used in machines that break the
liquid formulation into a fine mist or fog (aerosol) using a rapidly whirling
disk or heated surface. These formulations are used mainly for insect control
in structures such as greenhouses and warehouses and for mosquito and biting
fly control outdoors. Their advantage is easy way to fill entire enclosed space
with pesticide. And its disadvantages are; highly specialized use and equipment,
difficult to confine to target site or pest and may require respiratory
protection to prevent risk of inhalation injury.

Fumigants are pesticides that
form a gas when applied. Some active ingredients are liquids when packaged
under high pressure and change to gases when they are released. Other active
ingredients are volatile liquids when enclosed in an ordinary container and
therefore are not formulated under pressure. Others are solids that release
gases when applied under conditions of high humidity or in the presence of
water vapor. Fumigants are used for structural pest control, in food and grain
storage facilities, and in regulatory pest control at ports of entry and at
state and national borders.

In agricultural pest control, fumigants
are used in soil, greenhouses, granaries, and grain bins. Its advantages are;
toxic to a wide range of pests, can penetrate cracks, crevices, wood, and
tightly packed areas such as soil or stored grains and single treatment usually
kills most pests in treated area.

Its disadvantages; the target
site must be enclosed or covered to prevent the gas from escaping,
non-specific—highly toxic to humans and all other organisms and require the use
of specialized protective equipment, including respirators specifically
approved for use with fumigants.

Attractants include pheromones, a
chemical that is secreted by an animal, especially an insect, which influences
the behavior or development of others of the same species. Other attractants
are sugar and protein hydrolysate syrups, yeasts, and rotting meat. Pest
managers use these attractants in sticky traps and capture bags. Attractants
also can be combined with pesticides and sprayed onto foliage or other items in
the treatment area.

Systemic pesticides protect
animals against fleas and other external blood-feeding insects as well as
against worms and other internal parasites. A systemic animal pesticide is one
that is absorbed and moves within the animal. These pesticides enter the
animal’s tissues after being applied orally or externally.

Oral applications include food
additives and premeasured capsules and liquids. External applications involve
pour-on liquids, liquid sprays, and dusts. Most animal systemics are used under
the supervision of veterinarians.



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