AGR 3102 Principles of Weed Science Herbicide

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AGR 3102Principles of Weed ScienceHerbicide

• Muhammad Saiful Ahmad Hamdani

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Unit 6 Topics Covered

• Herbicides
• Adjuvants

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Why do not all agrochemicals go
in? Well some do quite easily, others not at
all.
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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.
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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.
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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.
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• 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

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Adjuvants

• Definition
• any substance in other formulation (in our
  case, its 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)

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• 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.

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Numerous types (or functions) of adjuvants

• Acidifiers
• Humectants
• Buffering agents
• Nitrogen fertilizers
• Colorants, dyes
• Penetrants
• Compatibility agents
• Spreaders
• Crop oils
• Stabilizers

• Dispersing agents
• Stickers
• Drift inhibitors
• Surfactants
• Emulsifiers
• UV absorbents
• Antifoaming agents
• Water conditioners
• Wetting agents

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• 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

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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.

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• Surfactants affect droplet spread

This has implications for uptake.
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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 slidevideo clip???
This discovery revolutionised the weed control
sector
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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.

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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.

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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).

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- penetrant
penetrant
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• 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

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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.

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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.