Transcript WITH ADJUVANTS

AGR 3102
Principles of Weed Science
Herbicide
Muhammad Saiful Ahmad Hamdani
Unit 6 – Topics Covered
Herbicides:
Adjuvants
Why do not all agrochemicals go in?
Well some do quite easily, others not at all.
1.
Differences in plant leaf shape & structure
Can be flat, thin, long, round, or needles.
Can also be horizontal, vertical or intermediate angle.
All these shapes and structures can affect herbicide
penetration into leaves.
2.
Existence of leaf cuticle and wax
Thickness of wax and cuticle affect the entrance of a
herbicide into a leaf.
A leaf with a thin cuticle allows the spray solution good
contact with the leaf surface.
On a leaf with a thick waxy surface, the spray solution tends
to stand up in droplets.
3.
Existence of trichomes/hairs
Hairs on the leaf surface tend to keep the spray
solution from entering.
The herbicide droplets stand up on the hair and do not
contact the leaf surface.
• Also other deposits like dust,
inorganic and organic compounds,
water,
microorganisms
• All these things affect herbicides retention &
absorption.
• How to overcome this problem???
• How to break/reduce all these barriers/obstacles???
• How to make herbicides work efficiently???
WITH ADJUVANTS
Adjuvants
• Definition:
“any substance in other formulation (in our case, it’s
herbicide) or added to the spray tank to enhance or
modify that formulation performance or application
characteristics”
• Some people call spray additives.
• Main functions:
1) improve ease of application/handling
2) enhance product efficacy (increase foliar adhesion
and cover, uptake or translocation of herbicides)
Formulation vs. Spray Adjuvants:
• Formulation adjuvants
Those included in the formulated herbicide
product by the herbicide manufacturer.
• Spray adjuvants
Added to the mixing tank primarily to improve
herbicide performance, aid in mixing, reduce
drift, reduce foaming, etc. Commonly used with
post-emergence herbicides.
• Our focus will be on spray adjuvants.
Numerous types (or functions) of adjuvants:
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Acidifiers
Humectants
Buffering agents
Nitrogen fertilizers
Colorants, dyes
Penetrants
Compatibility agents
Spreaders
Crop oils
Stabilizers
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Dispersing agents
Stickers
Drift inhibitors
Surfactants
Emulsifiers
UV absorbents
Antifoaming agents
Water conditioners
Wetting agents
• For simplicity, categorized into 2 basic groups:
1. Activator adjuvants:
Spray adjuvants used to enhance the biological
efficacy of herbicides.
• What they do: result in more herbicide being deposited,
adhered, retained, penetrated & absorbed into the
weeds.
• What they overdo: can, and often do, result in more
herbicide also being absorbed by the crop.
• Consequence: while increasing weed control, can also
increase crop injury by the herbicide.
• Examples:
Surfactants
• Derived from surface active agent
• Reduce water surface tension and improve
dispersion of the spray
• 2 groups: non-ionic type; organo-silicones.
• They are good dispersing agents, stable in cold
water, and have low toxicity to both plants and
mammals.
• Surface tension is so reduced that the spray
solution can penetrate the stomata on the leaf
surface.
Surfactants affect droplet spread
This has implications for uptake.
When the surface tension of a liquid is reduced by
adding other chemicals, it can flow through very tiny
spaces, such as the stomata on leaf surfaces.
Final slide…video clip???
This discovery revolutionised the weed control sector
Stickers
• Cause the herbicide to adhere to the plant
foliage.
• Reduces the possibility that rain will wash it
off before the herbicide can penetrate.
• Many blended with wetting agents so that
they both increase the spray coverage and
provide better adhesion action.
Crop Oils
• Crop oil concentrates, and methylated
seed oils, like surfactants, improve the
spreading of the herbicide solution.
• Being oil instead of water, they keep the
leaf surface moist longer than water.
• Allow more time for the herbicide to been
absorbed, thus increasing the amount that
will enter the plant.
Penetrants
• In general, penetrants make herbicides
“hotter” than it normal condition.
• Improve cuticular penetration by softening,
plasticizing, or dissolving cuticular waxes;
allowing herbicide to move underneath.
• Penetrants are often a complex mixture of
surfactant and oils (paraffinic petroleum or
modified vegetable).
- penetrant
+ penetrant
2. Utility/Spray Modifier Adjuvants:
Spray adjuvants used to modify the
physical characteristics of the spray
mixture.
• Long story short: they improve ease of
application/handling of the herbicides.
• Examples:
Drift Inhibitors
• Drift inhibitors or thickeners are used to control
drift.
• These may be powders, granules, or liquids that
cause the spray solution to be more
cohesive/thickened; less subject to wind shear
as it leaves the nozzles
• Also reduce the amount of very small spray
droplets.
Antifoaming Agents
• Air gap filling or mechanical agitation
in partially full tanks = excessive foaming.
• Foaming: interfere with herbicide flow and spray
• Antifoaming agents: silicone containing
products.
• They cause rupture of the air bubbles and
breakdown of surface foam.