Effective Pesticide Application

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Effective Pesticide Application

• Reeves Petroff
• Pesticide Education Specialist
• MSU Extension
• http//MTPESTICIDES.org

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A Basic Understanding of
Effective Pesticide Application
Should not be Confusing !

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Or Painful !

but it can be!!
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The Pesticide Application Process
The Spray Solution Atomization Transport
to Target Impaction / Deposition
Post-Impact Drop Behavior
Spreading, Retention, Penetration,
Translocation
Contact Action
Systemic Action
Biological Effect
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Spray Solution - Water

• Primary diluent
• Large percentage of spray solution volume
• Can have a negative influence on pesticide
  performance.

pH Minerals
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Acidity / Alkalinity (pH)
Affects a. The chemical stability of some
pesticides b. The dissociation and subsequent
penetration of weak-acid herbicides c. The
physical stability of the formulation upon
dilution
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Chemical Stability of Pesticides as related to pH
Many pesticides are unstable under alkaline
conditions that is pH levels above 7.0 Alkaline
hydrolysis. Stability is usually referenced in
terms of half-life.
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What is Meant by the Term Half-Life?
It is the time required for degradation to 50
of the original amount of the pesticide
It is used as a standard to describe the
relative stability of a pesticide.
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Examples of Stability relative to pH
Insecticides Bendiocarb Carbaryl Dimethoate Tr
ichlorfon
Half-Life 45 min pH 9 3.2 hrs pH 9 48 min pH
9 63 min pH 8
Fungicides Captan Iprodione
8.3 hrs pH 7 2 min pH 10 lt 1 hr pH 9
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Example of Instability
Alkaline Hydrolysis produced by high pH
Dimethoate

S (CH3O)2 - P - S -
CH2CONHCH3 S
(CH3O)2 - P - OH
H - S - CH2CONHCH3
At high
(alkaline) pH, OH_ ions attack the
molecule here
Producing
Molecules that are inactive as insecticides
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Chlorpyrifos

S N
(CH3O)2 - P - O Cl
Cl
Cl
N
S
OH Cl (CH3O)2 - P - OH
Cl Cl

At high
(alkaline) pH, OH_ ions attack the
molecule here

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Examples of pH and Stability
Herbicides Clodinafop Diclofop Flumiclorac
Half-Life 2.5 hrs pH 9 12 hrs pH 9 6 min pH
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pH also affects the Ohio group of herbicides
Weak Acids - OH
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Examples of Weak-Acid Herbicides
Clethodim (Select) Clopyralid (Curtail) Dicamba
(Banvel, Clarity) Endothal Fluazifop (Fusilade)
Glyphosate (Round Up, Accord,
Ranger, Glyphos) Imazamox (Raptor) Imazapyr
(Arsenal) Imazethapyr (Pursuit) MCPA Amine
Metsulfuron-Methyl (Ally, Escort) Paraquat Pic
loram (Tordon) Sethoxydim (Poast) 2,4-D Amine
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Dissociation of a Herbicide Molecule to an
ionic form at Alkaline pH
Picloram (Tordon)
At low pH At high pH
Neutral Molecule
Ionic Molecule

O C-OH
O C-O_
N
N
CL
CL
CL
CL
CL
CL
NH2
NH2
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Dissociation of a Herbicide Molecule to an
ionic form at Alkaline pH
2,4 - D
At low pH At high pH Neutral
Molecule Ionic Molecule

CL
CL
CL
O OCH2C-O_
O OCH2C-OH

CL
CL
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Dissociation of a Herbicide Molecule to an
ionic form at Alkaline pH
CL
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The effect of pH on Weak-Acid herbicides
Want Neutral or uncharged whole molecule Dont
want Charged or Ionic form
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Movement of Ionizable (Weak-Acid) Herbicides
Weak-Acid herbicides in an acid environment are
not ionized and can freely cross plant membranes,
upon entering the alkaline phloem (high pH) they
will become ionized. This traps the pesticide
in the phloem and will subsequently be
transported to active sites within the plant.
Vascular Bundle
Non-ionized pesticides freely cross plant
membranes
Leaves
pH 5 Xylem
150 cm / hr
Phloem 90 cm / hr
pH 8
Roots
Non-ionized pesticides freely cross plant
membranes
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Movement of Non-Ionized Herbicides
Once inside the plant, Non-Ionized herbicides
such as atrazine can move freely between xylem
and phloem, the xylem moves more rapidly than the
phloem so the net movement is in the direction of
xylem.
Vascular Bundle
Leaves
Xylem 150 cm / hr
Phloem 90 cm / hr
Roots
Non-ionized pesticides freely cross plant
membranes
Start
Source Nufarm
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Another Point To Ponder
The leaf surfaces of several weed species are
alkaline (high pH) Causes dissociation of
weak-acid herbicides resulting in reduced uptake
The condition is generally limited to
broadleaf weeds
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Surface pH of Weed Leaves
Dicotyledons
Velvetleaf Redroot Pigweed Catchweed
Bedstraw Tall Morningglory Pale Smartweed Common
Groundsel Teaweed (Prickly Sida) Wild
Mustard Black Nightshade
8.5 - 8.75 8.1 - 8.2 7.6 - 7.75 8.0 - 8.2 7.5 -
7.6 7.75 - 7.8 8.3 - 8.6 8.4 8.2
Monocotyledons
(most are nearly neutral at pH 7.0)
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Management of Leaf Surface pH
High leaf surface pH can be managed by
utilizing spray solutions that have been
acidified. Acidified spray solutions can easily
and effectively neutralize or even lower the pH
level.
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Elements of the Management of Water / Spray
Solution pH

• Know the water pH
• Know the susceptibility of pesticide
• Use acidifiers or adjuvants with acidification
  properties to adjust the pH level. Know that some
  things (copper containing fungicides) should NOT
  be acidified.
• Sulfonyl ureas??

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Hard Water
Ca, Mg, Zn NA, K ,
Mn Fe , Fe , Al
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Antagonistic Effects of Hard Water on Glyphosate
Molecules
Glyphosate and the cations will form a strong
complex which is physically large. This can
prevent or hinder uptake of the herbicide into
the plant, effectively reducing herbicide
activity.
O
O
O


-
Mg,
O P - CH2 NH2 CH2 C -
O P - CH2 NH2 CH2 C
-

O
O
Ca,
Sodium and Potassium (least effect) Calcium,
iron, magnesium and copper have most effect
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The Effect of Calcium on
Herbicide uptake by Setaria faberi
Untreated
Glyphosate (no Calcium)
Glyphosate CaCl2
Nicosulfuron (no Calcium)
Nicosulfuron CaCl2
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Dirt and other stuff
Dust Reduces the wettability
and coverage of applied spray. Mineral
composition of dust may antagonize some
herbicides. Organic matter may bind to some
herbicides. Clay constituency can neutralize
some herbicides. Exudates Some weeds called
Halophytes (Velvetleaf and Lambsquarter) have
salt or chalk glands which exude calcium
deposits onto the surface.
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Water Conditioning Strategies to Prevent
Antagonism of Weak-Acid herbicides
Removal of antagonistic ions by Ammonium
Sulfate Conditioning Acidification to reduce
the number of negatively charged herbicide ions,
or to select for the ionic charge with the least
potential for antagonism.
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The Pesticide Application Process
The Spray Solution Atomization Transport
to Target Impaction / Deposition
Post-Impact Drop Behavior
Spreading, Retention, Penetration,
Translocation
Spray Drift
Contact Action
Systemic Action
Biological Effect