Insect Pests of Vegetable, Tuber and Spice Crops

Exercise - 17

Exercise: STUDIES ON PESTICIDE USAGE AND DOSAGE CALCULATIONS

• In the present context the emphasis is on ‘Integrated Pest Management’ programmes and although application of pesticides on crops is considered as the environment polluting activity but insecticides are still a part of pest control programmes. The mandate is to make need based, judicious and safe use of these pesticides.

• Some of the aspects which should be taken care while using these pesticides are discussed here under:
• Handling and Mixing of pesticides:

While handling and mixing the pesticides the following care should be taken:

• Take care that there is no leakage or spills.
• Read the label carefully and make the necessary calculations for required dilution.
• Use proper equipments including the protective clothing.
• Don’t work alone while handling highly toxic pesticides.
• Mix the pesticides in a well ventilated area.
• Measure the quantities of the formulation required accurately and never use over doses.
• Don’t eat, drink or smoke during this process.

Pesticide application: Precaution to be taken during application of pesticides are as under:

• Use protective clothing and equipments.
• Ensure that the application equipment is in proper working condition.
• Apply pesticide at proper doses and proper time to minimize the residues.
• Guard against drift of pesticides to nearby fields, ponds, streams or live stock.
• Keep the pesticides away from the reach of children.
• Don’t blow the clogged nozzles with mouth.
• Clean the equipment by discharging enough water after use.
• Wash the clothing and protective equipments after spray.

Calibration of spraying and dusting equipments:

• Insecticide doses in any standard manual are in active ingredient (a.i.) bases e.g Kg/ ha or g/ ha. The equipment with the user can be of any make but he/she has to calibrate his/ her sprayer each time or season whenever there is overhauling or replacement of parts. The purpose is to find out spray fluid that is discharged per unit area so that correct quantity of active ingredient is applied for effective pest control.

For calibrating the equipment following parameters are required.

• Flow rate: Spray fluid/ dust discharged by the nozzle of a known orifice/ unit time (minute).
• Swath width: Spray spread on a flat surface in meters.
• Walking speed: Speed that can be maintained by a person throughout a day of 8h (m/min or Km/h).

Calibration of a manually operated sprayer:

• Mark a known area, say 100 m² (2 m x 50 m).
• Standardize the speed of the operator (say 60m/min)
• Fill the bucket or tank with known volume of water.
• Prime the sprayer and work it at optimum settings for say 5 min.
• Measure the volume of water discharged.
• Repeat five times and calculate the mean flow rate/ min
• Adjust the nozzle height by holding the lance at desired height (say 1.5 m) to obtain desired swath width (say 1m) which should be maintained during standardization/ field spray.
• Fill the tank with known volume of water
• Spray the marked area (say 100 m²) at standardized operating parameters.
• Note the volume of water used.
• Calculate the volume required for 1 hectare (1ha = 10000 m²)
• Thus the required quantity of active ingredient can be mixed in the volume calculated and sprayed on 1ha.

Pesticide calculations:

• Pesticide calculations may be required for the three common situations namely:
• Direct use of formulation
• A formulation is to be diluted in known volume of diluent.
• Specified active ingredient is to be applied per unit area.

1. Direct use of formulation (e.g dusts and granules):

Known factors:

A = Recommended dosage (a.i./ha)
B = Active ingredient (a.i.) in the formulation
Quantity of formulation (Q) required per hectare =?
Q = A/B x 100

Accordingly the quantity can be calculated for any unit area.
Example: Suppose a farmer has to apply 450g a.i./ha of carbofuran on a 2 ha area. Find out the quantity of carbofuran 3G required by the farmer.
Solution:
According to above formula,

A = 450 g or 0.450 Kg
B = 3
Q = 450/3 x 100
=15000 g or 15 Kg/ ha
= 15 x 2 = 30 kg for 2 ha

So the farmer requires 30 kg of Carbofuran 3G formulation to treat 2 ha area.

2. Preparation of known volume of spray fluid:

Known factors:

Volume of spray (V) (say 100 L)
Concentration (%) of the spray fluid (A)
Active ingredient (a.i.) in the formulation (B)
Quantity of the formulation (Q) required = ?
Q = V x A/B

Example: Prepare 100 L of spray fluid containing 0.04% chlorpyriphos from Durmet 20EC (a commercial formulation of chlorpyriphos).
Solution:

According to formula:

V = 100 L
A = 0.04%
B = 20
Q = ?
Q = 100 x 0.04/20
= 0.2 L or 200 ml

Hence 200 ml of Durmet 20EC is required to prepare 100 L spray fluid of 0.04 % strength.

3. Application of known quantity of a.i./ unit area:

Parameters:

A = Spray volume to be used (L/ha)
B = Discharge rate (L or Kg/ min)
C = Walking speed (Km/h)
D = Swath width (m)

Calculations:
i) If walking speed is in m/ min:

Spray fluid (A) required in L/m2 = B/(C x D)
or in L/ha = B/(C x D) x 10000

ii) If walking speed is in Km/h:

Spray fluid (A) required in L/ha = (600 x B)/ (C x D)
Discharge rate (B) of nozzle (L/ min) = (A x C x D)/600
Walking speed (C) = (600 x B)/ (A x D)
Swath width (D) = (600 x B)/ (A xC)

Problem: A farmer has to spray malathion 50EC @ 500 g a.i./ ha. Find the spray volume required for 1 ha, if the operator is walking at 3.6 Km/h; swath width is 1m and discharge rate is 1.5 L/min.
Solution:

Spray volume required (A) = ?
Discharge rate (B) = 1.5 L/min
Walking speed (C) = 3.6 Km/h
Swath width (D) = 1 m
Therefore, A = (600 x 1.5)/ (3.6 x 1)
= 250 L

So in this case a spray volume of 250 L containing 500 g a.i. (i.e. 1.0 L formulation) of malathion is to be sprayed over an area of 1 ha.
In these cases the concentrations of the pesticide are not important unless they are phytotoxic. To test phytotoxicity few plants can be sprayed in advance.