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Dara Park, Ph.D., Clemson University

Carrier Water Quality Influences Pesticide Efficacy

Dara Park darap@clemson.edu

Clemson Landscape Professional CERTIFICATION

¨  COMING THIS FALL ¨  Completely online ¨  MODULES:

ü  General information ü  Tree care ü  Water ü  Herbaceous plants & shrubs care ü  Plant identification ü  Turfgrass ü  IPM ü  Calibrations and Maintenance ü  Low Impact Development Strategies

¨  darap@clemson.edu

Learning Objectives LO1: What influences water composition? LO2: Common water quality issues that influence pesticide efficacy. LO3: How to measure pH.

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What influences water quality

FACTORS •  Mineralogy •  Climate •  Weathering Management practices!

• Use of acid-forming N fertilizers • Application of chemicals • Soil disturbance • Irrigation practices

Minerals influences water chemistry •  Naturally occurring due to release of Ca, Mg, Fe and HCO3 from carbonate-rich sedimentary rock.

Sources of components

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Sources of components

What influences water quality?

•  Reliance on lower quality water sources due to increased pressure on potable water sources

Increased Use of Alternative Water

•  Pathogens •  Elevated nutrient concentrations • Heavy metals •  Suspended solids • Dissolved organic matter

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Common Issues with Water Quality and Pesticide Efficacy

•  pH •  Hardness (presence of Ca, Mg and Fe) •  Alkalinity •  Iron •  Turbidity

What is pH?

•  AKA Per hydrogen, Power of the hydrogen, potential of hydrogen

• Concentration of H+ ions in water • Water equilibrium: H2O <=> H+ + OH-

Measure of the [H+] and [OH-]

Logarithmic scale: pH of 6 is 10X more H+ than pH=7

pH of 5 is 100X more H+ than pH=7

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<< acidic << >> alkaline >>

neutral = 7

Examples of a pH litmus strips.

Example of a pH meter.

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Common pH’s

Driven by biological activity: •  photosynthesis •  aerobic respiration •  anaerobic respiration

Diurnal changes in water pH

May June July Aug pH: 6.5 7.2 7.8 8.5

Example of seasonal change in water pH

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Example: Hydric pine flatwoods

Plant community influences pH

Where to purchase meters & litmus strips •  Many pool and aquarium stores sell pH kits.

•  Online: www.forestry-suppliers.com www.coleparmer.com www.amazon.com www.fishersci.com www.benmeadows.com

Monitoring pH • Most turfgrasses want soil pH ~5.5-6.5 • Optimum pH is species dependent

•  If out of range, indicates other problems • Nutrient availability • Hardness • Bicarbonates • Salinity

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pH effect on element availability

Pesticides and pH •  Most pesticides are stable at pH 4 to 6. • Some pesticides “decompose” pH > 7.

-alkaline hydrolysis

Pesticides and pH: alkaline hydrolysis Postemergent herbicides are weak acids: release H+ ions in water

• Glyphosate (Roundup) • Bentazon (Basagran) • Carbamates • 2,4-D (amine form)

• Partially dissociate when mixed with high pH water • The part that does not dissociate is readily absorbed by leaves • The part that is dissociated is – charged and can bind with cations.

•  antagonize most of the time • Work best at pH of 4-6 Exception: Sulfonylurea herbicides: Certain herbicides are susceptible to acid hydrolysis Keep the pH above 6.0

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Alkaline hydrolysis • Loss of pesticide efficacy: pesticide is chemically denatured. -examples:

-Dylox insecticide (half-life 4 days in pH 8.0) -Polyoxin D (Endorse) fungicide -Thiophanate methyl (Cleary’s 3336)

Always refer to product MSDS and label for

pH stability information.

Always check the MSDS…

…and the label.

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Case Study

0

2

4

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8

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4 5.5 7 8.5 10 Untr.Water Carrier pH

Dol

lar

Spot

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Bellewood GC, creeping bentgrass (~fairway), July 11, 2006.

b b b b

Banner MAXX @ 0.5 fl oz/M

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a

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5 7 9 Untr.Water Carrier pH

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Rutgers, creeping bentgrass (~green), July 19, 2007.

b b b

Banner MAXX @ 1 fl oz/M

a

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0

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4 5.5 7 8.5 10 Untr.Water Carrier pH

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pot

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)

Bellewood GC, creeping bentgrass (~fairway), July 11, 2006.

d d d

b

Daconil Ultrex @ 1.8 oz/M

ab a

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5 7 9 Untr.Water Carrier pH

Dol

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(#

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Rutgers, creeping bentgrass (~green), July 19, 2007.

b b b

Daconil Ultrex @ 3.2 oz/M

a

•  A way to compare how long pesticides take to break down. •  A half-life is the period of time it takes for one-half (50% hydrolysis) of the amount of pesticide in the water to degrade.

• Each half-life that passes reduces the amount of pesticide in the water one-half: 100% to 50% to 25% to 12.5%, etc.

Half-life

Chemical pH =6 pH= 7 pH=8 pH=9

Carbaryl 100-150 days 24-30 days 2-3 days 1-3 days

Captan 8 hours 10 min 2 min

Diazinon 70 days 29 days

Chlorpyrifos 35 days 22 days

trichlorfon 3.7 days 6.5 hours 63 min

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Suitability pH 3.5-6.0 Satisfactory for most spraying & can be

stored for 12-24 hrs. Not suitable for sulfonyl urea herbicides.

6.1-7.0 Adequate for immediate spraying. Short

term storage only (1-2 hrs). >7.0 Add buffer or acidifier.

What can you do? •  acids •  chelating agents •  surfactants •  ammonium sulfate

Buffering agents: will resist change in pH Spray immediately after mixing.

ALWAYS CHECK THE LABEL!

Plants can uptake cationic and anionic N chemical species.

•  Two main forms: • NO3

-

• NH4+

Roots interior rhizosphere

NO3-

HCO3- and or OH-

(nitrate ion)

H+

2H+

NH4+

NH4+

(ammonium ion)

Form of N taken up by plants influences soil pH

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Acid injection: principles

Acids that are typically used include: •  Citric •  Nitric •  Phosphoric •  Sulfuric

H+ (from acid) + HCO3- (in the water) è CO2 é + H2O

Comparison of acids Acid Amount to add for

each meq/L of alkalinity to result in water pH=5.8

Relative Cost

Relative Safety

Citric (granular) 9.1 oz /1000 gal $$$ minor

Citric (liquid) 14.5 fl oz / 1000 gal $$$ minor

Nitric 6.6 fl oz / 1000 gal $ severe

Phosphoric 8.1 fl oz / 1000 gal $$ moderate

Sulfuric 11.0 fl oz / 1000 gal $ severe

•  High mineral content (especially Ca, Mg, and Fe) in the water •  Reported as equivalent quantity of CaCO3

Water hardness

Classification Mg/l or ppm Grains / gal

Soft 0 – 17.1 0 – 1 Slightly hard 17.1 – 60 1 – 3.5 Moderately hard

60 – 120 3.5 – 7

Hard 120 – 180 7 – 10 Very hard > 180 > 10

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•  Ca and Mg bind with HCO3 to form insoluble salts •  Impacts soil pH •  Forms scales changing flow rates

Water hardness

These cations attach to – charged dissociated herbicide molecules (due to high pH) and form insoluble salt precipitates. Examples: •  Extremely hard water (600 ppm) can almost completely render 2,4-D at the low rate (4 -8 oz/A) ineffective

•  Dicamba •  Glyphosate •  Clopyralid (Lontrel)

Water hardness

Use ammonium sulfate: •  to keep pH low, •  SO4 binds up with the hard minerals

Organic acids (ex. Citric): •  a weak acid in which the conjugate base reacts with water cations. •  adds H+ ions too (lowers pH)

In both cases, add to tank before the herbicide.

Common ways to counter water hardness

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Is dilution the solution? NO

1 hard water ion can bind up ≥ 2 herbicide molecules

Instead: Decrease the volume of water used to apply •  Lower volumes means less antagonistic cations present. •  Use maximum label rates AS A LAST RESORT •  Non-ionic surfactants enhances herbicide efficacy but does not overcome the antagonism!

Common ways to counter water hardness

•  The concentration of CO32-

and HCO3- in water.

• bicarbonate (pH < 8.3, HCO3) • carbonate + bicarbonate (pH > 8.3, CO3 + HCO3)

Water alkalinity

•  Buffering capacity:

•  how well it resists or causes a change in water pH. •  measure of the ability of water to change pH of growing media •  high alkalinity will increase soil pH over time

Water alkalinity

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High alkalinity indicators

Alkalinity and pesticides

•  Certain herbicides are less effective at high concentrations (>300 ppm)

•  Example: •  2,4-D amine: >500 ppm

Alkalinity treatment options

•  Reduce water volume •  Reduce lime substrate

amendment rate •  Use an acid reacting

fertilizer •  Acid injection   •  Reverse osmosis or

deionization Alkalinity calculator – < http://extension.unh.edu/Agric/AGGHFL/Alkcalc.cfm>

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Acid injection

Bailey and Bilderback. 1998. Alkalinity. NCSU HIL #558

Iron (Fe)

•  Normal Range: 0-0.3 ppm

•  >0.2 ppm stimulate iron reducing bacteria

•  > 0.3 ppm = stains •  > 5 ppm, begin to have

films on plants

•  6th most abundant element in the universe, 4th in the earth’s crust!

Iron •  Bacteria slime clog boreholes, pumps and fittings •  Rust clog nozzles, filters, and lines. •  Brown leaf coatings reduce photosynthesis

• Minimal problem for turfgrasses but is a problem for ornamentals

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Managing Iron

Dependent on type of problem that exists •  Keep pH greater than 7.0 •  Aeration, then sediment filtration •  sediment filtration, then water softener •  KMnO4 , then sediment filter •  Chlorination, then sediment and carbon filtration

Turbidity

Suspended Solids •  organic particulate matter •  fine mineral fraction •  animal and plant material

Organic matter benefits and potential problems

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Adsorption

Portion of the label of RoundUp Pro:

Certain pesticides bind with soil (ex. Many post-emergent herbicides)

Microbial degradation

•  Degradation of pesticide by microorganisms (bacteria, fungi, algae, protozoa, etc).

•  Microbial degradation is a natural process, and at most times it is beneficial to the environment. The end products are mostly CO2, H2O and other organic and inorganic matters.

Turbidity Kd and Koc: Coefficients that deescribe the binding strength of herbicides

•  The ratio of herbicide bound to the soil when mixed with a water/soil slurry. Kd: soil sorption coefficient •  Dependent on soil characteristics

Koc: soil organic carbon coefficient •  independent of soil type

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Some Koc values

Herbicide Koc (mg/L) Turbidity effect Glyphosate 24,000 Y Paraquat 1,000,000 Y 2,4-d amine 100 N Dicamba 2 N

The higher the number, the more tightly bound, less effective

Test & Manage for turbidity

Options: • Wait until clear •  Use a filter • Determine best place in water

column to withdrawal •  Blend sources •  Use an additive to precipitate

Quick test: If you can see a quarter in the bottom of a 5 gal bucket of carrier water, then should be ok.

Saline water

•  Salts in irrigation water. A problem more along

the coast. •  Atlantic Intracoastal Waterway •  Tidally influenced creeks, streams, and rivers •  Saline aquifers

•  Can be assessed as water hardness too •  All glyphosate labels recommend adding

ammonium sulfate (AMS).

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Measuring Salinity Electrical Conductivity (EC)

Normal range: 0-0.78 dS/m 1dS/m = 1mmhos /cm = 1000 µS/cm

Total Dissolved Salts (TDS) Normal range: 0-500 ppm

Case Study: Irrigating with salt water affects the biology of soil-inhabiting insects

•  Can subsurface drip irrigation with salt water affect: •  the life history of insects? •  development? •  survival rate?

•  Salt concentrations: •  fresh water ( 0.1 ds m-1) •  saline water (~5 ds m-1)

•  Insects investigated: •  ground beetles – surface predator •  scarab beetle – underground organic feeder •  billbug – underground root feeder

Saline irrigation water did not affect biology of surface feeder

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5/15/2007

5/29/2007

6/12/2007

6/26/2007

7/10/2007

7/24/2007

8/7/2007

8/21/2007

9/4/2007

9/18/2007

Sampling dates

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freshsaline

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Saline irrigation water did not affect the biology of underground OM feeder

02468101214161820

5/15/2007

5/29/2007

6/12/2007

6/26/2007

7/10/2007

7/24/2007

8/7/2007

8/21/2007

9/4/2007

9/18/2007

Sampling dates

Sca

rabs

freshsalt

Saline irrigation water affected biology of root feeders

00.20.40.60.81

1.21.41.61.82

5/15/2007

5/29/2007

6/12/2007

6/26/2007

7/10/2007

7/24/2007

8/7/2007

8/21/2007

9/4/2007

9/18/2007

Sampling dates

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freshsalt

Summary

Before applying a pesticide: •  Check the label and MSDS for water quality compatibility issues. When in doubt call the company rep. •  Always test water pH before you add pesticide •  If the carrier water needs to be adjusted, do it before adding the pesticide •  Keep a log what you do.

Same goes for the irrigation water if needing to irrigate the pesticide in!

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For More Information

Full article and tables: http://www.clemson.edu/extension/horticulture/turf/pest_guidelines/water_quality.html

For More Information

Key:✔= OK. X= Do not use. NR = Not recommended but use soon after mixing if there is no alternative. Test = Test for compatibility.