HERBICIDE CALCULATION FOR SMALL AND LARGE

PLOTS

Why do we need to calculate herbicide rates?

Minimize crop injury by sticking to the labelled rate

Determine the accurate amount necessary to kill the targeted weed species

Improve efficacy and reduce the cost of chemical weed control

Minimize environmental side effects of over-dose and to make farming more economical

Herbicide volume per tank

After you have calibrated the sprayer to know your application

rate in Litres-per-hectare, divide that number into the Litres

applied with each tankful to find the hectare covered with each

tankful. Then multiply the hectare-per-tank by the herbicide

needed per hectare to find the herbicide to put in each tankful.

For example: Assume you calibrated your sprayer on a 250

meter course and the band width of your sprayer or swath width

was 2 meters, and you want to apply an herbicide at 4 kg of

active ingredient per hectare. The product comes as an 80%

wettable powder. If you apply 10 litres of spray to the course

(250 meter) after calibration.

Herbicide volume per tank contd.

Your calculations are:

1. Area sprayed in square meter =Length sprayed (meters) x Band

width(Swath width) =250 m x 2 m=500 square meter   

2. Determine Spray volume (L/ha)=(Volume (L)/ Area sprayed (m2)) x

10,000m2 m2=200L/ha

3. Determine no of spray tanks per hectare= Spray volume (L)/Spray

tank capacity (L) =200L/20= 10 tanks 

4. Determine the quantity (kg) of this product per hectare=4/0.80= 5

kg of product per hectare (5 kg/ha)

 

5. Determine the quantity of herbicide per tank= Rate of product

(kg/ha)/No of Tanks/ha=5/10=0.5 kg per tank

Herbicide dosage Calculation is based on the follow principles:

Quantity of commercial product needed to apply on a target (Q)

Rate of application of the active ingredient of the product (R)

Area to be treated with a given quantity of a product (A)

Concentration of the active ingredient of the formulation when the quantity to be applied is known (C)

Application rates: Herbicide rates may be given in terms of active ingredient

or acid equivalent per hectare treated, or as kilogram or volume of commercial product per hectare.

Recommended rates are usually given in kilogram active ingredient per hectare (kg ai/ha), and it is important to calculate the active ingredient content of the purchased herbicide

Active ingredient indicates the amount of non-acid herbicide in a formulation. Acid equivalent indicates the amount of an acid herbicide in a formulation; they are usually formulated as salts or esters of those acids

Calculation Steps:

Decide which commercial herbicide product to use

for best result, under particular circumstances (Liquid

formulations, e.g. e.g. WSC, or SL or dry

formulations e.g. W or WP )

Know the recommended rate of the herbicide

Know how much herbicide (active ingredient ) is

present or contain in the formulation

Herbicide rate per hectare:

Commercial products contain differing amounts of

active ingredients or acid equivalent. The amount of

herbicide formulation to use per hectare may be given

on the product label. If you have to calculate from the

active ingredient amount, use this method

Liquid formulation:

Liquid formulation-contd

For example: If 3.36 kg -per-hectare of

acid equivalent are needed, and the

product contains 240 grams-per-liter

(0.24kg/L), then divide 3.36 by 0.24 to get

14.025 liters-per-hectare, the amount of

product needed.

Dry formulations

Herbicide Calculations

Small plot application

Assuming you were to evaluate Primextra

formulated as 500 EC (500 g a.i/L). What

quantity should you measure for an

application requiring the product to applied at

the rate of 2.5 kg a.i./ha. Assuming an area of

50m2

Herbicide Calculations- Small plot application

Calculation:

Concentration =500g a.i/L =500g a.i/1000ml (Since 1L=1000ml)=0.5 g

a.i./ml

Rate of application given =2.5 kg a.i/ha= 2.5 x 1000 g a.i/ha=2500 g a.i/ha

1. Determine quantity of active ingredient per m2= 2500 g a.i/ha ÷10,000

m2=0.25 g a.i.

2. Determine the quantity of formulated primextra per square meter (m2)

= 0.25 g a.i.÷ 0.5 g a.i./ml

= 0.25 g a.i. x (ml) ÷ 0.5 g a.i= 0.5 ml of primextra

3. Determine the quantity of formulated primextra for 50m2= 0.5 ml x

50=25 ml of primextra

 

Herbicide Calculations- Large plot application

Assuming that you were to evaluate Primextra formulated as 500

EC (500 g a.i/L). What quantity of herbicide should you measure

for an application requiring the product to be applied at the rate

of 2.5 kg a.i./ha. Assuming an area of 10 ha

Calculation:

Concentration =500g a.i/L =0.5 kg a.i/L

Rate of application given =2.5 kg a.i/ha

1. Determine quantity of product used in one hectare= 2.5 kg

a.i/ha ÷ 0.5 kg a.i/L=5 litres

 2. Determine quantity of product for 10 ha=(2.5 kg a.i/ha x 10

ha) ÷ 0.5 kg a.i/L = 50 litres of product 

TABLE: 1. HERBICIDE DILUTION & EQUIVALENTS( RATE= 6L/HA)

SPRAYER CAPACITY

HERB. MLS/LOAD

MILK-TIN MEASURE

TOMATO-TIN MEASURE

REMARK

5L 150ml 1 2 ¼ CP 5

10L 300ml 1 ¾-2 4-4 ½ 10L

15L 450ml 2 ¾ 6 ½ CP 15

20L 600ml 3 ½ 8 ¾-9 CP3, JACTO