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Current Category » Introduction to Entomology

Pesticidal Formulations and Other Formulations and Their Applications in Field

The compound containing the toxicant must be formulated in a form suitable for use as a spray, dust or fumigant. The common formulations of pesticides are detailed here under.

1) Dust:

In a dust formulation the toxicant is diluted either by mixing with or by impregnation on a suitably finely divided carrier. The carrier may be an organic flour (Walnut shell flour, wood bark) or pulverized mineral (Sulphur, diatomite, tripolite, lime, gypsum tale, pyrophyllite) or clay (attapulgite bentonites, kaolins, volcanic ash). The toxicant in a dust formulation ranges from 0.65 to 25 percent. Dusts are defined as these having a particle size less than 100 microns and with increase in particle size the toxicity of the formulation decreases.

In the selection of a dust formulation its compatibility, fineness, bulk density, flow ability, abrasiveness, absorbability, specific gravity and cost should be taken into consideration. The dust should flow freely and must not cake or ball in the hopper. The application of dust must be done in a calm weather and early in the morning when the plant is wet with dew. The commonly used dust formulations are carbaryl 10% and quinalphos 1.5%.

Advantages:

1. It is cheaper pesticide formulation.
2. It is possible to apply on the field crops of those farms where the water supply is inadequate.
3. It can be applied easily with simple appliances.
4. It can be applied very fastly.

Disadvantages:

1. As these formulations are carried with air, there are many chances of drift problems.
2. The cost of carriers used in the preparation of this formulation is comparatively more.
3. Because of drift problem there is less deposition of the pesticide on treated plant surfaces and hence effectiveness is reduced.

2) Granular or Pelleted:

It is a type of insecticidal formulation prepared by applying liquid insecticide to coarse particles of porous material like clay, walnut shells. The particle size ranges between 250 to 1250 microns (0.25 mm to 2.38 mm in diameter). The formulations contain 2 to 10 percent concentration of the toxicant. The granules are applied in water or whorls of plant or to soil at the rate of 10 kg/ha. Granular formulations of systemic insecticides are used for the control of sucking and soil pest by application to soil. Whorl application is done for the control of borer pests of crops such as sorghum, maize and sugarcane etc.

Advantages:

1. There is very little drift.
2. There is no undue loss of insecticides.
3. Undesirable contamination is prevented.
4. Residue problem is considerably less as granules do not adhere to plant surface.
5. Release of toxic material is achieved over a longer period than does a spray deposit.
6. Water is not required for application.
7. Less harmful for natural enemies of the pest species.

Disadvantages:

1. It is not as effective as sprays against most crawling insects.

2. Scorching of plant parts may occur if the toxicant is concentrated in a smaller volume of carrier.

3) Wettable Powder:

Wettable powder is a powdered formulation which yields a rather stable suspension when diluted with water. The active ingredient in such a formulation ranges from 15 to 95 per cent. It is formulated by blending the toxicant with diluents such as attapulgite, a surface active agent and an auxiliary material such as sodium salts of sulfo acids. Sometimes stickers are added to improve retention on plants and other surfaces. Though the particles of a suspension adhere well to treated surface they do not penetrate and thus are easily washed off. However, suspensions are usually more effective than dusts. The requirements of a wet table powder formulation are.

1. Stability in storage and absence of caking.
2. Quick formation of suspension and slow settling out of solid particles.
3. Good wettability and spreading on treated surface and.
4. Retention on treated surface for a longer period.

4) Emulsifiable Concentrates:

It is a concentrated pesticide formulation containing organic solvent and emulsifier to facilitate emulsification with water. When EC formulations are sprayed on the plant parts, the solvent evaporates quickly leaving a deposit of toxicant from which water also evaporates. Some of the emulsifying agents in insecticide formulations are alkaline soaps, organic amines, sulfates of long chain alcohols and materials such as alginates, carbohydrates, gums, lipids and proteins.

The addition of emulsifying agents has the following specific purposes in insecticidal formulations.

1. Diluting of a water insoluble chemical with water is made possible.
2.  The surface tension of spray is reduced allowing it to spread and wet the treated surface.
3.  A better contact with insect cuticle is made possible.
4. Droplet size of the emulsion is greatly influenced by the kind and amount of emulsifier used.
5. The chemical structure of the emulsifier has influence on the stability and behavior of the emulsion.

5) Solutions:

It is a concentrated liquid pesticide formulation that may be used directly or require diluting. Many of the synthetic organic insecticides are water insoluble but soluble in organic solvents such as amyl acetate, carbon tetrachloride, ethylene dichloride; kerosene, xylene, pine oil etc. which themselves possess some insecticidal properties of their own.

6) Insecticides Aerosols:

In insecticide aerosol the toxicant is suspended as minute particles having size ranging from 0.1 to 50 microns in air as a fog or mist. This is achieved by burning the toxicant or vaporizing it with heat. The toxicant dissolved in a liquefied gas, if released through small hole, may cause the toxicant particles to float in air with the rapid evaporation of the released gas.

7) Fumigants:

A chemical compound, which is volatile at ordinary temperatures and sufficiently toxic, is known as Fumigants or it is a volatile insecticide that enters an insect via tracheal system. Fumgants are used for the control of insect pests in storage bins, buildings and certain insects and nematodes in the soil. Most fumigants are liquids held in cans or tanks and quite often they are mixtures of two or more gases. Phosphine or hydrogen phosphide gas is generated in the presence of moisture from a tablet made up of aluminium phosphide and ammonium carbonate. The advantage of using a fumigant is that the places not easily accessible to other chemicals can be easily reached due to the penetration and dispersal effect of the gas. However, the fumigants should be handled with at most care as the gas may prove to be toxic or may cause flavors in the treated crop. The commonly used fumigants are EDCT, methyl bromide, aluminium phosphide and hydrocynic acid.

8) Insectisides Fertilizers Mixturres:

The mixture generally constitutes addition of a granular insecticide to chemical fertilizer or spreading of insecticide directly on to the fertilizer. They are applied at the regular fertilizing time and provide both plant nutrients and control of soil insects. Urea 2% solution is mixed with compatible insecticidal emulsions and sprayed for supply of nitrogen to the plant and for realizing effective pest control. Many pesticides are rapidly broken down when mixed with fertilizers.

9) Poison Baits:

The poison baits consist of a base or carrier material attractive to the pest species and a chemical toxicant in relatively small quantities. The poison baits are used for the control of fruit flies, chewing insects, wireworms, white grubs in the soil, household pests rats in the field and slugs. This method is ideal under conditions where spray application is rather difficult. For successful poison baiting the attractivity, palatability, toxicity, stability and physical condition of the baits, as also the time, place and method of exposure must be considered. The high cost of the attractants and non-persistence for a longer period are some of the limiting factors in successful poison baits in pest control.

The common base used in dry baits is wheat bran moistened with water and molasses an attractant and a toxicant. The baits for fruit flies usually consist of methyl eugenol + DDVP or malathion with corn protein or yeast hydrolysate. For the control of fruit sucking moths fermenting sugar solution or molasses with a toxicant is used.

Current Category » Introduction to Entomology