Pesticide: Types and Classification

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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 (D):

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.

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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].

Granules (G):

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.

Pellets (P or PS):

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.

Repellents:

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.

Aerosols:

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 (WP):

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.

Emulsifiable concentrates (EC)

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.

Invert  Emulsions:

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.

Oil concentrates (OC):

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.

Gasoline   concentrates  (GC):  

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.

Soluble powders (SP):

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:

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:

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].

Flowable liquids (FL):

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.

Solutions and water soluble concentrates (S)

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.

Ready-to-use Low-concentrate Solutions (RTU):

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.

Utra-low Volume (ULV):

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:

A  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.

Liquid Baits:

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.

Poisonous baits:

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.

Encapsulated pesticides:

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].

Impregnates:

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:

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:

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.

Animal systemics:

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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