2. Herbicide formulations:
• The biological efficiency of a herbicide depends to a large extent on
the type of formulation it is made into.
• Formulation is a process by which the technical active ingredients
(principally responsible for herbicidal effects) are made ready to be
used by mixing with liquid or dry diluents by grinding and/or by
addition of emulsifiers, stabilizers and other formulation adjuvants
like activator, safeners etc.
• The development of a formulation depends on the physico-chemical
properties of the active ingredient to be formulated and of the inert
materials to be used in the formulation.
3. • A formulation is a mixture of active ingredient (principally
responsible for herbicidal effects) + carriers/solvents +
adjuvantsis called “ Technical material ” and is used for weed
control.
• The pure and concentrated form of a.i. or herbicide poses problems
in field use for various reasons.
• Therefore, no commercial or marketed product is manufactured
containing 100 % a.i..
• Hence they are mixed with inert carriers or solvents to obtain form
that can be used safely by the farmers.
• A formulation is a must for a herbicide or pesticide before it is
sold in the market.
4. Formulated product should possess
(a) required chemical stability (stable
active ingredient),
(b) retain desirable physical properties
like suspendability (of wettable
powders, no flocculation,
sedimentation or creaming),
(c) stability of emulsifiable concentrates
(no separation of contaminants present
in the colloidal system), and
(d) stable particle size (to maximize
biological activity, flow ability,
adhesivity, deposition on plant surface,
suspendability etc.).
5. 1) The formulation of herbicide makes the handling of toxic a.i.
convenient and safe.
2) It reduces the chance of direct contamination/exposure of
herbicide by humans and other animals.
3) It ensures greater bio-availability through better retention,
penetration and absorption of herbicide in the plant canopy.
4) It imparts greater efficiency/benefit with minimum risk.
5) In increases the shelf/storage life of a herbicide.
6) It reduces environmental pollution.
7) It saves resources and reduces price.
Why formulation?
6. TYPES OF FORMULATIONS
A)Dry Formulations
1. Granule (G)
2. Pellet (P)
3. Wettable Power (WP or W)
4. Soluble Powder (SP)
5. Water Dispersible Granule or Dry Flowable (WDG or DF)
B) Liquid formulations
1. Water-soluble concentrate (WSC)
2. Emulsifiable concentrate (E or EC)
3. Flowable or aqueous suspension (F, L or AS)
7.
8.
9. 1. Granules (G) usually contain < 10% a.i. and in rare cases upto
20% a.i. of herbicide in particular solid carriers suitable for direct
field application.
The technical active ingredient is mixed with or coated on, inert
carrier material of appropriate particle size.
The herbicide granules vary in size from 0.04 mm to 1.0 mm in
diameter.
Herbicide granules smaller than 0.04 mm are not used because they
drift easily with wind. Most carriers disperse into water.
Granules have no different problems and little foliage injury.
Mobility of herbicide within granules is an important aspect of
bioactivity.
Eg: Butachlor 5%GR, Ethyl ester 5%G
10.
11. 2. Pellets (P) or tablets (TB): Pellets are
similar to granules but tend to be more
uniform in size and shape. Pellets provide
a high degree of applicator safety.
Pellets are applied in the dry form, and
contain a small amount of active ingredient
(usually 10 to 20 percent by weight)
combined with inert carrier. Pelleted
formulations may be applied by hand or
mechanically, and are used for soil
treatment.
Ex.: Spike 20P (Tebuthiuron)
Pellets and tablets frequently are used for
spot applications.
12. 3) Wettable Powder (WP or W): Wettable powders are finely
ground solids, typically mineral clays, which forms suspension on
mixing with water. They provide an effective way to apply an
active ingredient in a water spray that is not readily soluble in
water. These dry preparations look like dust, contain a high percent
active ingredient (usually 50 percent or more) and are mixed with
water for application.
Wettable powders form a suspension rather than the true solution
when added to water. Good agitation (mixing) is needed in the spray
tank to maintain the suspension.
WP in general contains active ingredient + carrier (China clay) +
wetting/dispersing/suspending agent.
Ex : Atrazine 50 per cent WP, Simazine 50 per cent WP
13. 4. Soluble powder (SP): This is a dry formulation that contains a high
percent (usually above 50 percent) active ingredient. Soluble powders
look like wettable powders but they form a true solution when added
to water. Soluble powders are nonabrasive to equipment. Inhalation
hazard is a characteristic of this formulation.
Ex: 2, 4-D sodium salt 80%, Dalapon, TCA, etc.
5) Water-Dispersible Granule or Dry Flowable (WDG or DF):
WDG are another improvement over wettable formulations and they
contain smaller beads/granule which when added to water form
suspension.
Dry flowables are manufactured in the same way as wettable powders
except that the powder is aggregated into granular particles. They are
mixed with water and applied in a spray exactly like a wettable powder.
14. • During the mixing and loading process, dry flowables pour more
easily from the container and because of their larger granule size,
reduce inhalation hazard to the applicator.
• As the WDG are made of very fine particles (2-3 microns), they do
not choke spray nozzle. They give uniform distribution and
penetration into target surface.
• It is one of the latest formulations in great demand in many
developed countries.
• This dry formulation usually contains 70 to 90 percent active
ingredient.
• Constant agitation is required.
• Ex: Diuron 80 (Karmex)
15.
16.
17.
18.
19. B) Liquid Formulations
Liquid formulations do not exhibit the variety of physical forms
possible with dry formulations. However, liquid formulations differ
markedly in the nature of their characteristics that influence
selection, rate and method of application and environmental impact.
1.Water-Soluble Concentrate (WSC)/Soluble concentrates
(SC)/Soluble liquids (SL): This soluble contains about 85 % a.i.,
which can be dissolved in water and forms true solution. These
herbicides usually have an amine (ammonium salt) or mineral
salt in the molecule that enables water solubility. These
formulations are essentially non-volatile.
20. • Solvents and stabilizers are added to have mixture with
desired spray properties.
• Some types of solution concentrates are oil soluble.
• The herbicide must be soluble in a small quantity of
concentrated solvent to make packaging and shipment of the
formulation economical.
• It must also be completely and rapidly soluble in the carrier at
all temperatures and concentrate: carrier ratios that might occur
in the field.
Ex: Paraquat dichloride 24% SL
22. 2. Emulsifiable concentrates (EC): EC are usually clear solution
and form emulsion when added to water before spraying and the
resultant turns/ appears milky white. Emulsion is a heterogenous
medium of two liquids (stable or unstable) held together by a third
chemical called emulsifier or emulsifying agent, which helps to
mix a.i. with water.
Formulations of this type are highly concentrated and relatively
inexpensive; easy to handle, transport, and store; require little
agitation (will not settle out or separate) and are not abrasive to
machinery or spraying equipment.
Ex : Alachlor 50% EC, Butachlor 50% EC, Pendimethalin 30% EC,
Oxyfluorfen 24 % EC, Propanil 35% EC.
23.
24. 3) Flowable or Aqueous Suspension (F, L or AS)
The formulation has the same major characteristics as a
wettable powder it forms a suspension when added to water,
and it enables the application of water-insoluble herbicides in
water. They seldom clog spray nozzles and they need only
moderate agitation. Example: Diuron 4L
25. Dust (D) : A dust is a finely ground herbicide combined with an
inert or inactive dry carrier (ash, chalk, talc or clay). Usually has low
a.i.. Herbicides are not used in dust forms for fear of their drift
hazards, which may be intense.
Fumigants: Fumigants are volatile chemicals applied into confined
spaces or into the soil to produce a gas that will destroy weeds and
act as a soil sterilant. Ex: Vapam or Metham (Dithiocarbomate
group), EPTC (Eptam) (Thiocarbomate group), Diallate (Avadex)
26. ADJUVANTS
An adjuvant is an additive (usually in relatively low amounts compared to the
carrier) that improves or enhances application, performance, safety,
storage, or handling of an active ingredient.
Adjuvants include materials such as:
1. Surfactants- Surface Acting Agent/Reduces Surface Tension (spreaders,
stickers, emulsifiers, wetting agents), which increase surface contact, reduce
runoff and increase penetration through leaf cuticle
2. Anti-drift agents
3. Color and/or odor additives to discourage ingestion
4. Anti-freeze or other stabilizing chemicals to promote storage.
Many herbicides already contain adjuvants as part of their formulations.
Some of these formulations can be used directly whereas others need to be
applied in conjunction with one or more adjuvants. There are over 3,000
adjuvants available for use.
28. a) Surface application: Soil active herbicides are commonly
applied to the surface of the soil, where they may either left
undisturbed or incorporated into the soil physically. When left on the
surface, the applied herbicide should be able to move into lower 3.5 to
4 cm depth of soil under the influence of rain or irrigation water to kill
the germinating weeds. Eg. Substituted triazines, urea and anilide
herbicides.
Methods of Application of Soil-Active Herbicides
29. b) Sub-Surface Layering
It is the application of an herbicide in a concentrated band, about 7-
10 cm below the soil surface.
The technique has proved effective
in controlling perennial weeds like
Cyperus rotundus and Convolvulus
arvensis. Eg Carbamate and
nitralin herbicides.
The immediate use of the technique
is probably in orchards and
vineyards, besides certain wide-row
crops like sugar beet and tobacco.
30. c) Band Application
The band application of a herbicide constitutes its application to a
restricted band along the crop rows, leaving an untreated band in the
inter-rows. The band application of herbicides is primarily a cost
saving device since it reduces the quantity of herbicide in the ratio
of the treated band width to the crop row width.
Banded herbicide carrot plot at mid-season
31. d) Soil Fumigation: Herbicides used for fumigation are called as
fumigants. There are other soil-applied herbicides which must be
incorporated into the soil to prevent their rapid volatilization and/or
photodecomposition losses. Depending upon the nature of the soil
fumigant, it can be applied either
(1) by soil injection (chloropicrin)
(2) by releasing it under sealed, plastic covers (methyl bromide) or
(3) by direct soil surface application (Metham).
Soil fumigation under sealed plastic covers
32. v) Herbigation
Application of herbicides with irrigation water both by surface and
sprinkler systems. In India farmers apply fluchloralin for chillies
and tomato, while in western countries application of EPTC with
sprinkler irrigation water is very common in lucerne.
33. i) Blanket /Broadcast Application: Blanket (or over-the-top) it is
uniform application of herbicides to standing crops with disregard to the
location of the crop plants. Only highly selective herbicides are applied
by this method.
e.g. 2,4-D in wheat, rice , MCPB in pea, 2,4-DB in Lucerne, and
picloram in sugarcane
Methods of Application of Foliage-Active Herbicides
Blanket application
34. ii) Directed Spraying: It is the application of herbicides on weeds in
between rows of crops by directing the spray only on weeds avoiding
the crop. This could be possible by use of protective shield or hood.
For example, spraying glyphosate in between rows of tapioca using
hood to control Cyperus rotundus.
Post-emergence directed spray in cotton
35.
36. iii) Band treatment: Band application usually means treating a
narrow strip directly over or in the crop row. The space between the
rows is not chemically treated, but is usually cultivated for weed
control. This method reduces the chemical cost.
iv) Spot treatment: Spot treatment is treatment of a restricted area,
usually to control an infestation of a weed species requiring special
treatment.
It is usually done on small areas having serious weed infestation to
kill it and to prevent its spread. Rope wick applicator and
Herbicide glove are useful here. Soil sterilant treatments are
often used on small areas of serious perennial weeds to prevent their
spread.
38. v) Protected Spraying: Non-selective herbicides can be employed to
obtain selective weed control in distantly planted vegetables and
ornamentals either by covering the non-target plants before application
of the herbicide with plastic or metallic covers or by spraying herbicide
underneath a hooded or shielded sprayer. This method is called protected
spraying. This is expensive and laborious. However, farmers are using
this technique for spraying glyphosate to control weeds in jasmine,
cassava, banana.
39.
40.
41.
42. Combinations of Herbicides: Often two or more herbicides are
applied mixed with the following possible aims :
a) To broaden the spectrum of weed control,
b) To get synergistic action,
c) To prevent rapid detoxification of active herbicide, and
d) To improve herbicide safety.
Not all herbicide combinations are compatible.
Herbicide Rotation: It is the practice of following a systematic,
rotational sequence herbicide use in the same field.
It may involve either
(i) change of herbicide in the same crop or
(ii) change of crop in the same field so that a different herbicide
could be used.
43. Herbicide application techniques: Generally, herbicides are
applied in the form of solution or granules.
Pesticide applicators:
Non pressurized applicators include the water can, granular
applicator,
controlled – droplet applicator and direct contact applicators such
as rope wicks and wipers.
Hydraulic (pressurized) applicators usually need water to work.
Lever operated Knapsack sprayer, motorized or ground driven
applicators are examples.
44. Operation of the Knapsack sprayer: A spray is defined as liquid
discharged into particles and scattered as dispersed droplets.
Herbicide application is directed to soil in case of pre-planting and
pre-emergence herbicide and to foliage in case of post-emergence
herbicide. Compressed air (70-275 Kpa) forces the liquid from the
pressure chamber through the hose of the nozzle. The nozzle turns
the liquid into droplets, which aid in uniform coverage of the weed
or soil.
Selection of nozzle: Impact nozzles cause less drift problems.
They are used for residual herbicides applied to the soil. For
systemic translocated herbicides, where thorough wetting of
stems and leaves is not required, an impact nozzle or fan nozzle
is recommended.
For contact herbicides, use of a hollow cone nozzle, an impact
nozzle or a fan nozzle operated at 275 Kpa is recommended.
45. The types of nozzles shown above are even fan, standard flat
fan, deflector (x2), hollow cone and solid cone nozzles.
Impact nozzles
46. Nozzles are designed to create and direct drops of spray, which land and
form a shape or swath. Different types of nozzles create swaths
(footprints) of different shapes.
These swaths are from even fan, standard flat fan, deflector, hollow cone
and solid cone nozzles.
The first row shows the downward spray patterns of each of the nozzles.
The second row shows the 'footprint' on the ground of each nozzle.
The third row shows the volume of spray deposited across the swath.
47. Mixing: The concentrated active ingredient of a herbicide must be
mixed thoroughly with water (the carrier).
• When using a wettable powder, agitate the solution to prevent the
herbicide from settling out. Fill the spray tank about half full with
water.
• Add the measured herbicide to the tank, and then fill the tank
completely with water.
• Mix the contents of a knapsack sprayer tank by shaking it.
• Amount of water used is not critical as long as the sprayer has been
calibrated to deliver certain rate.
48. Spraying:
1) Do not spray when the wind is too strong. If you must spray when it is
windy, hold the nozzle close to the ground (within 50 cm) to prevent
the droplets from being blown away during calibration of the sprayer
and during actual field spraying. Always walk downwind so that any
spray blown off the crops is carried away from you.
2) Soil applied herbicides should not be trampled (walk backward while
spraying)
3) Use a soft material to clean the blocked nozzles. Never clean nozzle
with wire or pin.
4) A nozzle height of about 50 cm from the target to the ground is
ideal. Avoid missing strips or overlapping spray swaths.
5) While spraying maintain a constant walking speed.
49. Herbicide drift: Herbicide drift occurs when the smaller drops in
the spray are carried away from the target by the wind or when
vapour from the volatile herbicide is carried away during or after
sprayings.
Growth regulator herbicides (2,4-D, MCPA) cause the greatest drift
damage. Crops such as tomato, cotton, lettuce and tree fruits are
particularly sensitive to them.
Herbicide drift can be avoided by :
1) Spraying only when a light wind is blowing away from
susceptible crops.
2) Using the minimum pressure required for the nozzles to operate
properly.
50. 3) Holding sprayer nozzles close to the target.
4) Leaving a 10 m wide strip unsprayed between the crop and any
field where sensitive crops are growing.
5) Other weed control methods can be applied to the unsprayed
strip.
Cleaning the sprayer:
1) Clean the sprayer with clean water to remove most of the
chemical. A household detergent can be added to water for
cleaning. Pour this out and add clean water again.
2) Operate the pump for at least 10 strokes and pour out the
remaining water.
3) Repeat these procedures two or more times.
