Calculation based on pesticides
Being highly toxic, pesticides are not sold in its pure form. They are subjected to dilute with any carrier to avoid the hazards of poisoning to applicator or human being. The pure forms or technical grades are only used in analytical and toxicological studies. Pesticides are commercially manufactured in various formulations (by adding various additives) like emulsifiable concentrates, water-dispersible powders, dusts, granules, solutions etc. The strength or active ingredient is mentioned on the label.
What is active ingredient?
It is the chemical in commercial products which is directly responsible for its toxic effect.
What is acid equivalent?
It refers to the formulation that theoretically can be converted to the parent acid. Some herbicides are active organic acids like phenoxy acetic acid, picloram & chloramben and some are generally supplied in the form of their salts and esters as in 2, 4-D.
Let us see some commercially available pesticides
Insecticides: Endosulfan 35EC, Malathion 50EC, Metasystox 25EC, Dimethoate 30EC, Phorate 10G, Carbafuron 3G,
Herbicides: Atrazine 50 WP, Simazine 60 WP, Paraquat 24WSC, Fluchloralin 45EC, Alachlor 50EC or 100G, Butachlor 50EC or 5G, Glyphosate 41WSC, Propanil 35EC, 2, 4-D Ethyle ester 18 & 35%, 2, 4-D Amine salt 58 & 72%, 2, 4-D Sodium salt 80 & 85P etc.
Fungicides: Carbendazim 50 SC, Carbendazim 50 WP, Copper Oxychloride 50WP, Difenconazole 24.9EC, Dithianon 5, 10EC, Dithianon 5SC, Hexaconazole 5, 10EC, Hexaconazole 5 SC, Mancozeb 80, 75 WP, Miclobutanil 10 WP, Propiconazole 10, 25 EC, Tebuconazole 24.9 EW, Tricyclozole 75 WP etc.
Pesticides are recommended in three ways for its field application such as amount of pesticides per hectare (kg/ha), amount of active ingredient or acid equivalent per hectare (kg a.i./ha) and concentration of solution to be applied ( eq 0.07 % of endosulfan).
Before application or purchase of pesticides it is always strike in the mind of farmers that how much amount of insecticides or herbicides or fungicides etc would be required for application on their farm of definite size so that he could parches only the required amount . Let us see the methods for calculating the pesticide dose with some example.
If recommended as kg a.i./ha:
Rate of herbicides is given mainly in terms of a.i. or a.e. /ha
Rate of application
Quantity of material required per hectare = ----------------------------------- X 100
Active ingredient in %
Example: Find out the quantity of simazine 80WP to be sprayed in one hectare area if rate of application is 3 kg a.i. /ha
Quantity of simazin/ha =3/80 x 100 = 3.75 kg WP/ha
For the calculation of this type we must know the a. i. present in the commercial product.
If recommended as kg/ha:
Experience has shown that to spray one hectare with a hydraulic nozzle sprayer in good working condition and a 15 liter sprayer, one will need 300 liters of solution, i.e. 20 sprayer loads.
Example: To control grasses, 5 liter of propanil should be applied per hectare. Its mean
1 liter = 1000 ml
20 sprayers (15 L each) per ha
5000 ml/ 20 = 250
i.e. 250 ml per 1 small Kap-sac sprayer and 20 loads will be required.
If recommended as per cent concentration:
Volume of spray X Per cent strength of pesticide
solution (liter) solution to be sprayed
Amount of pesticide= ---------------------------------------------------------------------------------
per cent strength of pesticide given (a.i./l or kg)
Example: Amount of malathian 25 EC when applied as 0.025 per cent solution
300 × 0.025
= 0.3 liter or 300 ml/ ha
By Pearson's square method:
Example: To prepare 0.05 per cent mixture from endosulfan 35EC.
To get the required amount of insecticide and water, substract the smaller figure from the higher ones (i.e., 0.05-0=0.05 and 35-0.05=34.95), diagonally.
Put 0.05 opposite EC at d and 34.95 opposite water at c point.
This mean that to make 0.05 % solution out of the endosulfan 35 EC, we have to require 0.05 part of endosulfan + 34.95 part of water.