Cecil Tharp
MSU Pesticide Education Program
Bozeman, Montana
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That pesticide didn’t have any residual. I need to reapply every few weeks.
That chemical doesn’t work at the labeled rates. I need
to double or triple the rates!
My pests are resistant to this chemical!
They are full of it! That pesticide doesn’t work!
Water
Primary diluent
New Term
Why water quality is important!
• 1 pint or 1 quart per acre
• 30 GPA application volume
• 99% and 93% of spray solution
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pH
Hardness
TDS
Turbidity
Alkalinity
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Is the measure of the concentration of
hydrogen ions (H+) and hydroxide ions (OH-)
in a solution.
Scale is logarithmic from 0 - 14
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Hydrogen predominates (acidic < 7)
Hydroxide predominates (alkaline > 7)
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Dissociation is the breaking down of a complex molecule into simpler units.
Efficacy often goes down when molecules are dissociated. Plants often won’t
absorb the chemical as well. At times this may totally inactivate the pesticide.
 pH 6 – 7 is ideal for most pesticides but it can vary.
Weak Acid Herbicides are the most susceptible to alkaline (high ph)
dissociation
 Roundup® (glyphosate)
 Pursuit® (ammonium salt of imazethapyr)
 Liberty® (glufosinate ammonium).
 2-4D salt
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At pH > 7, many organophosphate, pyrethroid,
or carbamate insecticides can break-down in a
matter of hours or minutes
‘Oxamyl’
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Some pesticides are vulnerable to breaking
down in a low pH solution.
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Sulfonyl urea (SU) herbicides (Escort, Ally) tend to
break down more rapidly when the pH is < 6 (acid
hydrolysis).
This is more common in forested mountain
areas of western MT.
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Consult the LABEL to see if there
are any warnings about water pH.
Know the pH of your water
source.
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Purchase a “pocket pH meter” and
use it or other testing kits which are
widely available.
Forestry Suppliers $55.95
Science Lab.Com $79.97
If > 8 or < 6 you may need to add
buffering agent
Use spray solution ASAP
Add acidifier if needed
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Total Dissolve Solids (TDS) is the measure of
all dissolved mineral cations and anions.
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Generally in Montana, hardness (cations only) is
used to measure ionic water quality concerns related
to pesticide performance.
Gives water it’s taste
Positive Charge (cations)
Negative Charge (anions)
Calcium (Ca++)
Magnesium (Mg++)
Sodium (Na+)
Sulphate (SO4-)
Chloride (Cl -)
Bicarbonate (HCO3-)
How is TDS measured?
Calcium =
666 ppm
Sulphate =
2434 ppm
Magnesium =
234 ppm
Chloride=
32 ppm
Sodium =
130 ppm
Bicarbonate =
346 ppm
TOTAL = 3842 ppm.
TDS > 500 mg/L (ppm) is salty to taste
Types Of Water
 Drinking water <500 TDS (EPA)
 Fresh Water : <1,000 TDS
 Brackish : 1,000-5,000 TDS
 Highly Brackish : 5,000-15,000 TDS
 Saline : 15,000-30,000 TDS
 Sea Water : 30,000-40,000 TDS
 Brine : 40,000-300,000+ TDS
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Hardness is the concentration of multi-valent
cations (positively charged ions from minerals)
Cations bind with negatively charged pesticide
molecules
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Positively charged pesticide molecules are converted
to a negative charge when they are broken into
smaller units from hydrolysis.
pH and hardness work together to reduce efficacy
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Forms insoluble salts
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WHO Hardness Classification Chart
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If the sum of the concentration (ppm) for the
cations exceeds 150 ppm action should be
considered:
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2,4-D amine (> 150 ppm)
 totally deactivated at 500 ppm)
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Dicamba (> 150 ppm)
Glyphosate (> 150 ppm)
Clopyralid (>150 ppm)
sethoxydim ‘Poast’ (>150 ppm)
Imazethapyr ‘Pursuit’ (>150 ppm)
Reduces efficacy of many
surfactants
Scale may plug sprayer
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Add an adjuvant containing sulfate or organic
acids as they bind with hard minerals
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non-ionic surfactants increase efficacy
Add ammonium sulfate (8.5 – 17 lb / 100 gallons)
Alkalinity or
Bicarbonate
Waters
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Associated with sodium
> 500 ppm & high pH
Affects 2,4-D
Affects “dim” herbicides
• Poast - sethoxydim
• Select – clethodim
• Achieve -tralkoxydim
Bicarbonate Waters
- Solution • Use maximum allowed rate
• Apply during optimal growth stage
• Adjuvants
- Non-ionic Surfactant (NIS)
- Acidifiers/buffers
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Turbid water, or water containing suspended
solids, soil, or organic matter can reduce
effectiveness of postemergence herbicides.
Measured in Nephelometric Turbidity Units
(mg/L)
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Many pesticides bind to soil
particulates (high soil sorption
potential)
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Glyphosate (24,000 KOC)
Permethrin (100,000 KOC)
Bifenthrin (240,000 KOC)
Paraquat (1,000,000 KOC)
Diquat
Harbors microbes which can further
break down pesticides
Particulates can clog filters and
nozzles
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Drop a quarter to the bottom
of a 5 gallon bucket.
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If you can’t see the quarter then
the water must be treated or not
used.
Locate an alternative water
source
Install inline filters
Make sure intakes are not at
bottom of tanks
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Check the water pH
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If greater than 7.5 consider buffering agents
 Especially if your pesticide is an organophosphate,
carbamate, or a weak acid herbicide (product label pH
warnings!)
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Test the hardness of your water
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If less than 6.0 (not likely) and using SU’s
If over 150 ppm then consider adding adjuvants or
alternative water source especially if using 2,4-D,
glyphosate, dicamba, clopyralid
Test the turbidity of your water
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If water is murky consider an alternative water source.
Adjuvants
• Additives to improve performance
• Acidifiers
• Buffers
pH
• Conditioners
• Ammonium Sulfate (AS)
• Non-ionic surfactants (NIS)
Hard
Water
www.herbicide-adjuvants.com
1. Test the water
2. Reduce Water
Volume
3. Use maximum
allowed rate
4. Spray ASAP
after mixing
5. Adjuvants
Wilbur Ellis testing kits
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Great Falls Field Office (406-727-4500)
Dillon Field Office (406-683-5355)
Billings Field Office (406-248-1176)
Navigate to Purdue University Water Quality
webpage at
http://www.ppp.purdue.edu/Pubs/PPP-86.pdf
Gemplers.com
Cecil Tharp
Pesticide Education Specialist
406-994-5067
ctharp@montana.edu
www.pesticides.montana.edu