Optimizing Herbicide Performance

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Optimizing Herbicide Performance

• David Jordan
• North Carolina State University

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Optimizing Herbicide Performance

• Optimize the things you can control
• Minimize the risk of things you cannot control
• Know what you have and what works best on what
  you have
• Know whether you have resistant biotypes

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Preplant Burndown or Incorporated and
Preemergence Performance

• Must have water for activation
• Must spread risk so that you get some activation
  of herbicides not incorporated
• Overlapping PREs (2 wks ahead, at planting, with
  POST in season)

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Optimizing Herbicide PerformancePostemergence
Herbicides

• Weed size
• Herbicide rate
• Nozzle selection
• Spray volume
• Adjuvant selection
• Water quality
• Compatibility
• Mixing interval

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Need to spray at this time!
Might get lucky at this time
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We have to use comprehensive systems of PRE and
POST herbicides. Roundup Ready, LibertyLink, and
conventional systems have a place and all three
can be very effective. BUT, it takes multiple
applications of different modes of action in all
three systems to get us where we need to be
because of resistance!
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• Spray Nozzles
• Application technique is very important.
• An excellent herbicide program can fail due to
  poor application.
• Nozzle selection and proper operation are
  critical components of herbicide application.

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Nozzles
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• Factors affecting nozzle flow rate
• Orifice size
• Pressure
• Specific gravity of spray solution
• Viscosity of spray solution primarily concerned
• with drift control agents (no conversion
  factors)
• Effect of increase in viscosity of spray
  solution
• Nozzle flow rate Decrease
• Spray angle of nozzle Decrease
• Droplet size Increase
• example in next slide
• principal behind drift control agents

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Results from Research in North Carolina with
Drift Control Agents

• Glyphosate
• Glufosinate
• 2,4-D
• Dicamba

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• Importance of Droplet Size
• Droplet size affects coverage
• Smaller droplets better coverage
• Droplet size not critical for PPI or PRE
• Droplet size important for POST
• Droplet size affects potential for spray drift
• Smaller droplets greater drift potential

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• Spray Droplet Size
• Expressed as VMD (volume median diameter)
• VMD of 200 um means 50 of spray volume composed
  of droplets lt 200 um and 50 of volume composed
  of droplets gt 200 um

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Effect of droplet size on spray coverage
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Spray volume (GPA) equal in both cases.
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• Importance of Droplet Size
• Droplet size affects coverage
• Smaller droplets better coverage
• Droplet size not critical for PPI or PRE
• Droplet size important for POST
• (reason POST herbicide labels often specify type
  of nozzle to use, or not to use)

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• AI TeeJet air injection spray tips
• Produce tapered flat fan pattern
• Large, air-filled droplets
• Promoted for drift management
• Available only as110-degree angle
• Designated as AI
• Output rated as GPM at 40 PSI
• Nomenclature
• AI 11002 VS

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Spraying Systems Greenleaf
Technologies
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• AI TeeJet air injection nozzles
• Used for broadcast applications
• Recommended pressure 30-115 PSI pressure
  affects droplet size
• Promoted for drift management good for
  soil-applied and systemic POST
• 4. Typically 20-inch boom mounting
• 5. Recommend 30 to 50 overlap
• 6. Suggested minimum height,
• 20-inch spacing 15 to 18 inches

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Types (or functions) of Adjuvants
Surfactants Nitrogen fertilizers Spreaders Disp
ersing agents Stickers Compatibility agents Crop
oils Foaming agents Wetting agents Foam
suppressants Emulsifiers Buffering
agents Penetrants Acidifiers Stabilizers Drift
control agents Humectants Dyes, colorants Water
conditioners UV absorbents Some overlap
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Basic Types of Spray Adjuvants Activator
adjuvants enhance biological efficacy
of the pesticide Utility/spray modifier
adjuvants modify physical characteristics of
spray mixture
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Activator Adjuvants (enhance biological efficacy
of the pesticide) Surfactants Crop oils Ammonium
fertilizers
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Ionic Classes of Surfactants 1. Nonionic - no
charge 2. Anionic - negatively charged 3.
Cationic - positively charged 4.
Amphoteric - positively or negatively charged,
depending on pH Types 2, 3, 4 primarily are
formulation adjuvants. Type 1 commonly used by
growers.
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• Organo-Silicone Surfactants
• Tremendous capacity to reduce surface tension
• Excellent droplet spreading
• Sometimes called super wetters
• Typically blended with non-ionic surfactants
• Used at much lower rates than non-ionic
  surfactants
• NIS 0.25 by volume
• OSS 0.05 by volume
• Expensive

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Crop Oil Adjuvants 1. Crop Oil a. Misnomer as
the origin of the oil is not from plants. It
is a derivative of paraffin-based petroleum
oil. Also called phytobland oil. b. Consist
of oil plus 1 to 2 surfactant to aid in
mixing in water. c. Promote penetration of
pesticide through waxy plant
cuticle. d. Delay droplet drying time e. No
longer used for herbicide applications
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Crop Oil Adjuvants 2. Esterified Seed
Oils a. Produced by reacting fatty acids from
seed oils with an alcohol to form esters.
b. Methyl or ethyl esters then combined with
a surfactant. Typically make methyl esters,
and product referred to as methylated seed oil
(MSO). c. MSO often boosts herbicide activity
more than a COC or POC. d. Not commonly used
in NC, but labels of certain products specify
an MSO. Osprey and Option are examples of
herbicides requiring MSO.
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• Ammonium Fertilizer as an Adjuvant
• Most commonly used are ammonium sulfate (AMS)
• and urea-ammonium nitrate (UAN).
• Less commonly used is ammonium polyphosphate
• (10-34-0).
• Ammonium ion thought to be largely responsible
  for
• beneficial effect on herbicide performance.

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• Ammonium Fertilizer as an Adjuvant
• AMS typically recommended at 2.5 to 4 lb/A or
• 8.5 to 17 lb/100 gal spray solution.
• UAN typically recommended at 2 to 4 qt/A.
• Labels which recommend use of an ammonium
• fertilizer usually specify the fertilizer in
  addition to
• NIS or COC. Fertilizer does not replace other
• adjuvants
• Several products on market that contain AMS
• surfactant drift control agent.

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• Alleviation of Hard Water Antagonism of
• Glyphosate with Ammonium Fertilizer
• Hard water contains cations such as Ca2
• and Mg2. Reduces efficacy of glyphosate.
• These cations compete with isopropylamine
• in formulated glyphosate isopropylamine
• salt for association with glyphosate anion.
• Resulting salt, such Ca-glyphosate, is not
• absorbed well.

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• Alleviation of Hard Water Antagonism of
  Glyphosate with Ammonium Fertilizer
• Hard water contains cations such as Ca2 and
• Mg2. Reduces efficacy of glyphosate.
• These cations compete with isopropylamine in
• formulated glyphosate isopropylamine salt for
• salt for association with glyphosate anion.
• Resulting salt, such Ca-glyphosate, is not
• absorbed well.
• Ammonium ion, if added to tank and agitated
  before adding glyphosate, may precipitate Ca and
  Mg ions, ultimately increasing weed control.

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Primary Utility/Spray Modifier
Adjuvants 2. Defoaming agent Definition a
material that eliminates or suppresses foam in
the spray tank Commonly called
defoamers American Society for Testing and
Materials
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• pH of Spray Solutions
• Can affect degradation rate in solution
• Can affect solubility and polarity of
• ionizable herbicides (more polar, or
• less lipophillic, when ionized)

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• Alkaline hydrolysis
• Some insecticides degrade rapidly in high pH
  water can even degrade in spray tank
• Generally not a problem with herbicides we
  basically do not worry about water pH when
  spraying herbicides
• pH can affect water solubility of some
  herbicides, which potentially could affect
  absorption

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Adjuvant Selection Can Be Very Confusing!
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• Adjuvant Selection Can Be Very Confusing
• Hundreds of products available
• Multiple-component adjuvants
• No governmental regulation
• Very limited unbiased testing
• High profit item for distributors
• Herbicide manufacturers reluctant
• to recommend specific brands
• Exaggerated claims, testimonials,
• high pressure sales

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Selecting an Adjuvant 1. Read herbicide
label. A. If label specifically says to not use
adjuvant, then dont use one. B. If label
does not mention using adjuvant, follow
personal experience, or seek advice of
herbicide sales rep or extension. C. If
specific brand of adjuvant recommended on
herbicide label, use it if possible. D. If
herbicide label recommends only a type of
adjuvant, use recognized name brand
from reputable distributor. Compare on basis
of active ingredient and cost.
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Selecting an Adjuvant 1. Read herbicide
label. 2. Consider previous weather conditions,
crop status, weed species, and weed size. 3. Go
slowly with the premium adjuvants.
Costly, probably no more efficacious than
standard adjuvant. Conduct your own trials.
Consider a water analysis. 4. Watch out for
the snake oil man. If claims sound too good to
be true, there is high probability they are not
true.
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• Time in Tank
• Glyphosate and water quality
• Compatibility