|
Agri-Net Guyana | Overview | Agricultural Institutions | Sub-Sectors | Support Services Statistics | Projects and Special Programmes | News & Current Events | Links |
|||||||||||||||||||||||||||
Leslie A. Munroe, Entomologist PESTICIDE FORMULATIONPesticides contain an active ingredient (a.i) and inert material(s), which serve as carriers for the a.i. The preparation of the active ingredient in a form suitable for use is referred to as a formulation. Types of formulationPesticides are applied primarily as sprays, dusts and granules. Sprays: Several pesticides dissolve readily in water and can be applied as solutions. Some are, however, insoluble in water and require formulating with surface-active agents or special solvents. Examples of common spray formulations are listed below.a) Wettable powders (WP) are concentrated dusts containing a wetting agent to facilitate mixing of the powder before spraying. To ensure good mixing, most powders should be pre-mixed with a small amount of water to form a thin paste. Normally, WP formulations are not compatible with other types of formulations. b) Emulsifiable Concentrates (EC) are concentrated oil solutions with enough emulsifier added to make the concentrate mix readily with water for spraying. c) Water Soluble Powders (SP) unlike WP’s, water soluble powders dissolve immediately when mixed with water. They also do not require constant agitation, as do wettable powders. Dusts and granules: A toxic agent with an inert diluent is the most common type of dust formulation in use. They are the simplest formulation of pesticides and the easiest to apply, however, they are the least effective of pesticide formulations, since they have a low rate of deposit on the target. Granules are small pallets which contain an active ingredient in a carrier, usually inert clays. The range from 2% to 25% a.i. Calibrating the SprayerProper calibration of sprayers will ensure the uniform distribution of pesticides and adequate crop cover.The following steps should be followed for the calibration of knapsack sprayers. 1. Stake out a test area in the field. 2. Place a known amount of water in the spray can. 3. Establish the spray swath. 4. Walking at normal speed, spray the test area. 5. Measure the length of the test area sprayed. The application rate, in litres/hectare is then calculated. Area sprayed = swath width (m) × distance traveled / 10,000 Application rate = volume sprayed / area sprayed EXAMPLE Spray swath = 5m Distance traveled = 50mVolume sprayed = 5litres Area sprayed 5 × 50 / 10,000m² = 0.025ha Application rate 5.0litres / 0.025ha = 200litres CALCULATING PESTICIDE DOSAGES Most pesticides do not come in a ready-to-use fashion, therefore, they need to be diluted to obtain the desired concentration before they can be applied. It is, therefore, important that one knows how to determine what quantity of pesticide to mix with a given amount of water. Similarly, some chemicals may come in a ready-to-use form, e.g. dusts, however, the applicator will need to work out how much of the product to use on a given area, based on the recommended dosage. Pesticide dosages may be expressed as Weight of active ingredient per unit area e.g. dusts – 2kg a.i/ha OR Percent active ingredient in a spray solution e.g. E.C. or W.P. – 0.05% Malathion solution. Determination of weight of A.I. per Unit Area
A =B×100 / C EXAMPLE 1: What quantity of sevin 5% dust is required to control aphids on 1ha of beans if the recommended dosage is 2.5kg a.i per hectare. Note: 5% Sevin dust means that every 100kg of the product contains 5kg a.i. SOLUTION: 5kg a.i (C) are contained in 100kg1kg a.i (A) are contained in 100 / 5 2.5kg a.i (B) are contained in 100 / 5 × 2.5 Quantity required (A) = 100× 2.5 / 5 = 50kg of formulation. Sprays: The same principle used for dusts and granules can be applied for sprays. From your calibration you will know the volume of spray required per hectare, thus with this knowledge you can determine the quantity of formulated pesticide required. EXAMPLE 2: What quantity of Sevin 80%W.P is required to control caterpillars in a 5 ha corn plot if the recommended dosage id 2kg a.i. per ha and the spray volume is 250 litres per ha. SOLUTION: 80kg a.i. are contained in 100kg of commercial produce. 1kg a.i are contained in 100kg / 80 of commercial produce. 2kg a.i are contained in 100 × 2kg / 80 = 2.5 kg of commercial produce. This is the amount required to treat 1ha. Thus the amount required to treat 5ha is 2.5 ×5 = 12.5kg. The spray volume required for 5ha is 250 × 5= 1250 litres. If the sprayer is of 20 litres capacity then the number of spray loads required is 1250 / 20 = 62.5. The amount of commercial product per spray load (kg) is 12.5 / 62.5 = 0.2kg or 200g.
Determination of Dosage as Percent Active Ingredient in Spray Solution To determine the percent active ingredient (E) in a given quantity of spray solution (Q) containing a known quantity of commercial formulation (P) of known. %Concentrate = Quantity of formulation in spray solution (P) / Concentration of commercial formualtion(R) × Total amount of spray solution(Q) EXAMPLE 3: What is the concentration of a 100 litres spray solution which contains 1kg of a 50% a.i. wettable powder. E = 1 × 50 / 100 = 0.5% This formula can be rearranged to determine the quantity of a formulation required to mix with a known quantity to obtain a desired concentration of spray. Quantity of formulation = % Concentration required (E) / Concentration of commercial formulation (R) × Total amount spray solution (Q)
EXAMPLE 4: Calculate the amount of malathion 50% E.C required to prepare a 10 litres spray solution of 0.05% concentration. SOLUTION: 0.05 × 10,000 / 50 = 10mL CONVERSION TABLES
This page was created and maintained by the National Agricultural Research Institute, Mon Repos, East Coast Demerara, Guyana.
If you have any questions or comments, please, contact us at nari@networksgy.com
|
|||||||||||||||||||||||||||
|
Agri-Net Guyana | Overview | Agricultural Institutions | Sub-Sectors | Support Services Statistics | Projects and Special Programmes | News & Current Events | Links |
|||||||||||||||||||||||||||