1. A
Seminar on
Advances in herbicide application
techniques
Rajkamal Patel
Ph.D. (Scholar)
Dept. of Agronomy
Dr. M. C. Bhambry
Principle Scientist
Dept. of Agronomy
2. Herbicide application
Herbicide should be applied as
uniformly/evenly as possible on the foliage or to the
soil. It depends on the :
Quality and suitability of spray equipment
Skill of operation/spray man in using the equipment
Effect of environmental factors such as wind, rainfall,
RH etc
Volume rate
3. Volume rate depends on the situation
where application is made. It tells about the following
three usual categories of spray/application
i. High volume spray (400 l/ha and above)
ii. Low volume spray (5 to 400 l/ha) However, it is
generally 100 to 200 l/ha for ground application
and 15-75 l/ha for aerial portion
iii. Ultra –low volume spray (up to 5 l/ha)
4. Spray Symbol
Spray volume (l/ha)
Field crops Trees and bushes
High volume HV >600 >1000
Medium volume MV 200-600 500-1000
Low volume LV 50-200 200-500
Very low volume VLV 5-50 50-200
Ultra low volume ULV <5 <50
Source: Weed Science
T. K. Das
Different classes of spray
5. Kinds of herbicide application
1. Overall/ blanket application
herbicide is applied uniformly
over the entire area of the field for complete control
of weeds. It could be achieved through ppi, pe or Poe.
2. Band application
In band application, a band or narrow
strip over the crop rows as against the entire area of
field is applied with herbicide.
3. Directed spray
It is application of herbicide to directed
towards the ground or weeds to reduce its contact
with crop. It is achieved by covering the row space and
spraying herbicide at the inter-row space. Used in high
value plantation crops such as tea, apple, grape, citrus
and in several field crops like maize, cotton, sugarcane.
6. 4. Overhead spray
In overhead spray, application is over
the crop as against application directed specifically to
weeds. It is usually a Poe treatment, but hardly
practiced for herbicide. For parasitic dodder control
or defoliation of trees it may be adopted.
5. Spot application
Herbicide is applied to patches of
weeds in the field or elsewhere. It could naturally be a
Poe application.
6. Basal bark application
For controlling trees and shrub,
herbicide is applied by sprayer to the bark encircling
basal foot or trunk or just paintbrush the basal bark
with concentrated solution of herbicide or herbicide as
such.
7. 7. Direct contact application
Directed contact application is
achieved by rope-wick applicator, herbicide glove, roller
applicator or re- circulating sprayer. Helps non selective
herbicide to be applied selectively in crop by means of
direct contact with tall growing weeds.
8. Controlled droplet application
Controlled droplet
application is achieved by special sprayer, e.g. CDA
sprayer, micron herbisprayer.
8. Kinds of sprayer
On the basis of various forms of energy
utilize to atomize spray liquid, the sprayer are classified
inio :
i. Hydraulic energy sprayers : Foot sprayer, knapsack
sprayer, hand compression sprayer, stirrup pump
sprayer, rocker sprayer etc use hydraulic energy for
atomization of spray liquid. A reciprocating pump or
air compression pump is operated mechanically or
manually and, as a result, pressure is built up for
compression of the spray liquid. The pressurized liquid
is forced to pass through the nozzle, which atomizes
the liquid into droplets.
ii. Gaseous energy sprayer : Mistblower, motorised
knapsack sprayer.
iii. Centrifugal energy sprayer : Spinning disc, CDA
sprayer, hand held motor operated sprayer, micron
herbisprayer.
9. Kind of sprayers
Sprayers, on the basis of power
requirement for running or operating them, are broadly
divided into :
I. Manually- operated sprayers :
Manually operated sprayers are knapsack
(backpack) sprayer, foot sprayer, rocker sprayer,
hand compression sprayer, stirrup pump sprayer,
bucket sprayer, pot sprayer etc.
They mostly use hydraulic energy.
A reciprocating pump or air compression pump is
operated mechanically or manually and pressurize
the spray liquid for compression.
The compressed liquid passes forcefully through
nozzle, which atomize the liquid into droplets.
10. Foot sprayer/ Pedal pump sprayer
Requires more than one person normally three
persons one for pumping by foot, one to hold the
delivery tube and the third man to spray the
herbicide.
In cropped situation, more than one person may be
required to hold up the long delivery pipe.
Droplets output at the outlet is more and
therefore, its volume rate is higher, normally 600-
500 litres/ha.
Used in pre planting and pre-emergence herbicide.
11.
12. Knapsack (backpack) sprayer
Requires one person for spraying herbicide in the
field.
Loaded on the back of worker during operations
Tanks may be of plastic or metal.
Droplets output at the outlet is less than foot
sprayer and, therefore, its volume rate is lower
normally 300-350 litres/ha.
A single person can spray an area of 1.0 – 1.5
hectares by this sprayer in one day.
13. Parts of knapsack sprayer
a) Spray tank
• Contains carrier /diluents /liquid
• It is low capacity tank containing 15-20 litres of
water.
• Spray tank made up good quality plastic tank.
• The inside bottom of the tank should be flattened
or should have slope.
b) Pressure pump
• It atomizes the liquid/ fluid.
• Pressure pump is installed inside the spray tank,
but has provision for pumping or pressurizing from
outside the tank by moving the pump handle
vertically up and down.
15. c) Delivery/ Discharge system
• Water/ solution move through this system from the
tank to the target area under pressure and forms
uniform sized droplets are mist.
i. Delivery tube/ hose
• A delivery tube is usually a small plastic tube.
• The length (1.0 – 1.5 m) is just sufficient to move
the spray lance around or to and fro for
comfortable spraying when the tank is on the
back of spray man.
• It is attached with the tank in one end and the
spray lance on the other.
16. ii) Spray lance with cut-off device
• Spray lance is a metal tube and has a cut-off device
at its junction with the delivery tube.
• The lance and cut-off device are made up off the
same metal (brass, stainless steel, aluminium or
copper).
• The cut-off when pressed by hand and allows water
to flow from the delivery tube to lance under pressure
and ultimately water is discharge through nozzle.
iii) Nozzles
The nozzle performs 4 basic functions :
• Atomize liquid into droplets.
• Disperses the droplets in a specific pattern.
• Meters liquid at certain flow rate.
• Provides hydraulic momentum.
17. • The cost of nozzle is less compared to the cost of
herbicide/pesticide and equipment, but the choice of
nozzle play a great role for achieving higher application
efficiency of herbicide in the field.
• The efficacy of herbicide will depends mostly on the
type of nozzle, equipment and technique.
• If the discharge takes place through a narrow angle
from the nozzle, the swath would be naturally narrow;
however, it is wide from a wide angle discharge.
• Nozzles are different kinds, viz., flat fan, flood jet,
solid cone, swirl/ hollow cone, tapered cone, triple action
cone, etc.
18. Common features of flat fan and flood jet nozzles
S/N Flat fan nozzle Flood jet nozzle
1 Better. Good.
2 Smaller droplets. Bigger droplets.
3 Less swath width/area covered. More swath width/area covered.
4 Less area is sprayed per unit time,
say, 1 ha/day.
More area could be sprayed per
unit time, say, 1.5-3.0 ha/day.
5 Less pressure-dependent (30-40
psi) and, therefore, frequently /
often recommended.
More pressure-dependent. Central
portion remains untreated if
pressure is less.
6 Flat fan nozzles are designed to
give a higher rate of deposit at
the center of spray than at the
two ends of spray.
The reverse is true for flood jet
nozzles. They are designed to give a
higher rate of deposit at the two
ends than a center of the spray.
7 Most suitable for low are medium
volume work and penetrate the
dense foliage better.
Suitable for large volume work parti
cularly on bar soil.
20. Adjustable nozzle
• It is generally used on hand guns.
• They can be used to produce various type of spray in
cone and jet form.
• They are mostly used in orchards and trees where
target is far from the operator.
Double swirl spray nozzle
• This type of nozzle is used for spraying in two
different direction simultaneously.
• Nozzle like hollow cone or flat fan can be fitted with
different types of tips.
Rotary nozzles
• It usually produce more uniform droplet size spectrum
than conventional nozzles.
22. II. Power-Driven/Operated sprayer
A. Motorized small-powered sprayers
• AS the name suggest, motorized small-powered
sprayer is a mechanical modification of manually-
operated knapsack sprayer, foot sprayer or wheel-
mounted sprayer and has less power required.
• In motorized small-powered sprayer pumping is done
through small generator.
• The generator/blower produces airflow, which
pressurizes the spray liquid to flow out of tank.
• The spray liquid flow through delivery tube and
reaches to nozzle where it breaks up by strong air
into fine droplets.
• It has higher water capacity to the tone of 100
litres or more.
23. B. Tractor-mounted sprayers
• It has large capacity sprayer containing large volume
of liquid ranging from 200 litres to 2000 litres or even
more.
• Depending on the power supply of tractor and length
of boom, swath width and area sprayed per unit time
vary.
• An area of 4-8 hectares could be sprayed per day by
this sprayers.
• To avoid the entry of tractor into crop field, it could
be bit modified.
• Along delivery tube could be attached to the multy-
nozzle boom from the spray tank mounted on a tractor
and spraying may be carried out with multy-nozzle
boom manually (by a person) on the crop field,
roadside or elsewhere, while tractor moving on road or
near by to crop field.
25. Role of Droplets
Droplets play an important role towards achieving
higher efficacy of herbicide.
Efficiency of an application depends to a large extent
on the droplets’ size, density and contact angle, spray
concentration and retention.
Droplet size is highly important if pesticide are to be
applied efficiently with minimum contamination of
environment.
26. Classification of spray according to droplet size
SN Volume mean diameter (u) Droplet size Classification
1.
<25
Fine aerosol
2. 26-50 Course aerosol
3. 51-100 Mist
4. 101-200 Fine spray
5. 201-400 Medium spray
6. > 400 Coarse spray
Source: Weed Science
T. K. Das
27. Accepted optimum droplet size for different
targets with minimum or no drift hazard
SN Target Droplet size (u)
1. Flying insects 10-50
2. Insect on the foliage surface 30-80
3. Plant diseases/fungi 30-150
4. Weeds (Post emergence) 100-300
5. Soil and where drift to be avo
ided (soil insects, weeds pre-e
m. / pre planting)
250-500
Source: Weed Science
T. K. Das
28. Effective number of droplets per cm square
on the treated surface
SN Pesticide Minimum number of
Droplets
1. Insecticide 20-30
2. Fungicide 50-70
3. Pre-emergence herbicide 20-30
4. Other herbicide 30-40
Source: Weed Science
T. K. Das
29. Tips towards achieving effective spraying / weed control
1. Choice of sprayer
• Foot sprayer or knapsack sprayer with flood jet nozzle
may be adopted for spraying a large area per unit time.
• For smaller area of 1 ha/day, knapsack sprayer with
flat fan nozzle can be opted.
2. Calibration of sprayer
• Knowing the requirement of water for spraying a unit
area under a particular situation is a pre-requisite for
effective application of herbicide.
• The volume of water required per hectare is depended
on the kind of herbicide, type of sprayer and nozzles
fitted with the sprayer, spray pressure and speed of
application
30. • Knapsack sprayer, based on calibration, has been found
that it requires lower volume rate normally 350-400
liters/ha as compared to the foot sprayer, which may
require 600-800 litres/ha.
3. Choice of herbicide
• The past history of weed infestation in the crop fields
(For pre-planting/pre-emergence application) and survey
(for post emergence application) and their identification
under un existing crop is highly necessary for
recommendation of herbicide.
•The herbicide recommended should be available in the
market and it needs to be purchased from a reliable
source/shop with obtainment of a proper cash receipt.
31. 4. Choice of nozzle
• Use flat fan nozzle preferably for post-emergent
systemic/translocative herbicides.
• Otherwise both flat fan and flood jet nozzles could be
used for both per-planting and pre-emergence application.
• Nozzle tip or nozzle may be replaced on non-uniform
pattern of non-uniform pattern of spraying.
5. Pressure supply
• Uniform spraying is a pre-requisite for achieving an
effective control of weeds
• Pump pressure affect nozzle output, spray pattern and
droplet size.
• To maintain constant pressure and achieve uniform
spraying in the field, a pressure regulator valve can be
fitted before nozzle in the spray lance.
32. 6. Mode of spraying
• “well planned is half done”.
• Some ground works/planning are required for better
and effective application of herbicides.
• In a bigger field 1 ha or more, better divide the entire
field into smaller ones the number off which should be
equal to the number of tanks of spray liquid required
for spraying such area as per calibration made.
•This will maintain volume rate required and ensure
uniform application of herbicide.
33. Maintenance and Repairment of Sprayer
Good maintenance of a sprayer and its sprayer parts
prolongs, while mishandling decreases their lives and
accuracy of performance.
I. Water being used in the sprayer should always be clean
and free from solid particles and it should pass
through the filter/sieve placed at the inlet of spray
tank for filling the tank.
II. Better use separate sprayers for herbicides and other
pesticides namely, insecticides, fungicides,
nematicides.
III. The spray pump along with delivery system should be
thoroughly washed with water once spraying is over for
a herbicides.
34. IV. Leakage of any kind should be checked and
prevented or repaired with proper washer and
gasket.
V. Clogging of nozzle is of frequent occurrence while
spraying, but don’t insert a matchastic or a wire or
the like in nozzle hole to clean nozzles.
VI. Don’t through the spray lance on the ground.
VII. Once spraying is over for the day, wash the spray
pump, tank and delivery system thoroughly with
clean water for 2-3 times.
VIII. Dry the sprayers properly in the sun.
35. Special Devices for Herbicide Application
1. Hood/Shield
In woody crops like sugarcane and cotton, paraquat can
be made selective by using hood.
2,4-D kills only broad-leaved weeds/plants and is
selective to monocotyledonous crops.
It is hardly used in broad-leaves crops like cotton,
jute, potato, but it could be made selective to these
crops using a “hood/shield” placing at the broader
space between rows.
2. Direct contact Application (DCA)
i. Rope –wick applicator (RWA)/Weed wick wiper
It is device for herbicide application in the field for
achieving selectivity for a non-selective herbicide.
36. The capillary action and gravitational flow allow the
chemical to move out of a reservoir on to nylon rope-wick
and chemical is rubbed from soaked rope on to the tall
weeds (Dale,1980).
It renders almost complete wetting of the weed stand
and makes control easier.
ii. Herbicide glove
It is specially designed for safe application of non
selective herbicides to control tall weeds like Avena
ludoviciana/fatua (wild oat), Phalaris minor (littleseed
canary grass) particularly at the flowering stage when
they are clearly identified.
While moving along the crop rows, the stem just below
the panicle of each weed is squeezed to receive
herbicide droplets on the plants.
38. 3. Controlled Droplet Applicator (CDA)
The only way to reduce the spray volume and to keep
the same droplet density as in higher volume is to reduce
the droplet diameter which is brought about by
controlled droplet applicator.
E.J. Bals coined “ CDA” and is called “the father of
ultra low volume spray.”
CDA is logical extension of ultra-low volume (ULV) and
very low volume (VLV) spraying concept.
Objective of CDA is to apply minimum volume of spray
toward effective and economic control of pests.
39. In CDA, a specially designed high speed spinning disc
(flat, concave or convex) rotary atomizer with woven
mesh cage or perforated cylinder produces the required
size of droplets for a particular applicator.
The rotary atomizer use centrifugal energy and breaks
up the spray liquid into fine droplets and the controls the
range of droplet sizes to necessarily very narrow.
One of the major benefits of using CDA is to reduce
significantly the volume of spray liquid applied to crops.
It covers the larger area in less time due to wider
swath.
