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Published byAshley Harvey Modified over 9 years ago
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Pesticides in the Environment Environmental Fate of
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What is Pesticide Environmental Fate? How and where a pesticide enters the environment How long it lasts Where it goes.
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Pesticide Losses at Application Method of application 55% 45% Rate Timing Number of applications Placement
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Pesticide Characteristics Chemical characteristics determines behavior Four main characteristics: –Solubility –Adsorption –Half-life (aka. Persistence) –Volatility
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Solubility Amount of chemical that can be dissolved into a solution Parts per million (PPM) > 30 ppm = high tendency to leach or runoff. Tordon = 400- 430 2,4-D = 890 Assert = 1370 Ally/Escort –1750 (pH 5) – 2790 (pH 7) –213,00 (pH 9) Paraquat = 7000 Roundup = 12,000
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Runoff vs. Leaching
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Adsorption Binding Organic matter More organic matter = more binding by less- soluble pesticides
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Measuring Adsorptivity - K oc organic carbon partition coefficient - universal index how tightly a pesticide will bind to the organic matter in the soil.
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Adsorptivity and Solubility Less water-soluble pesticides More adsorbed Less likely to leach or runoff
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K oc of Common Pesticides Banvel – 2 Stinger – 6 Pursuit – 10 Tordon – 16 2,4-D – 20 Assert – 35 to 66 2,4-D Ester – 100 MCPA – 110 Broadstrike - 700 Methyl Parathion – 5100 Lorsban - 6070 Treflan – 7000 Roundup – 24,000 Buctril – 10,000 Capture – 216,500 Paraquat – 1,000,000
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Generally, solubility and adsorption are inversely related As solubility increases; absorption decreases Always the exception: Roundup and paraquat. Both are highly water soluble but bind very tightly to soil.
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Solubility & Adsorption Some things to ponder Read the label! –Look for restrictions based on soil type. Example – Tordon restriction on loamy sand to sandy soils. Calibrate! Calibrate! Calibrate! Do not over apply Know the soil type in the area you are spraying. Conduct a soil test….
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Texturing your soils
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Even a jar test will give you an idea!
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Degradation –Microbes (#1) –pH (#2) –Sunlight –Rate applied Degraded over time to produce CO 2, H 2 O, N, P, Su, Expressed as “half-life.” Time required for that substance to degrade to one-half its previous concentration. Persistence (Residual)
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Malathion - 1 2,4-D - 10 Banvel – 14 Ally, Amber – 30 Stinger - 40 Assert – 45 Roundup - 47 Tordon – 180 Spike - 360 Paraquat – 1000 Degradation values of some common pesticides (1/2 life in days)
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Pesticide Drift Physical drift caused by small droplets –Improper nozzles –Improper pressure Chemical drift –Volatilization
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Comparison of Micron Sizes (approximate) 2000 m 850 m 420 m 300 m 150 m 100 m #2 Pencil lead paper clip staple toothbrush bristle sewing thread human hair
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Driftability of Spray Droplets of Varying Sizes 10 feet Crosswind @ 3 mph 20 20 50 50 100 150 8 ft 22 ft. 48 ft. 178 ft. 1065 ft. 8 ft 22 ft. 48 ft. 178 ft. 1065 ft. \
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Nozzle Drop Size Classes Very Fine to Fine < 200 um Medium to Coarse – 200 to 450 um Very Coarse > 450 um
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Tip Spray Selection by Drop Size Turbo TeeJet Flat-fan
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Evaporation of Droplets Wind High Relative Humidity Low Temperature Low Relative Humidity High Temperature Fall Distance
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Evaporation and Deceleration of Various Size Droplets* Droplet Diameter (microns) Terminal Velocity (ft/sec) Final Drop diameter (microns) Time to evaporate (sec) Deceleration distance (in) 20.0470.3<1 50.25171.83 100.913379 1501.75016 2002.4672925 *Conditions assumed: 90 F, 36% R.H., 25 psi., 3.75% pesticide solution
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Strategies to Reduce Drift Avoid adverse weather conditions Consider using buffer zones Consider using new technologies: –drift reduction nozzles –drift reduction additives –shields, electrostatics, air-assist Increase drop size Increase flow rates - higher application volumes Use lower pressures Use lower spray (boom) heights
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Turbo Drop Nozzle Greenleaf Technologies Air Induction (AI) Venturi pressure reduction chamber Droplets are filled with air and expand when leaving tip Better coverage $10.00
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LI 700 R-11 Tallow Amine Water Adjuvant Influence on Spray Pattern (Note Uniformity of Pattern) Source: FRI New Zealand
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Volatility Conversion of a liquid or solid to a gas Lower vapor pressure = lower volatility 2,4-D ester = 13 mPa Banvel = 4.5 mPa Banvel SGF = 1.6 mPa Tordon = 0.082 mPa Roundup = 0.010 mPa
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Volatility is also affected by: Weather –High temperatures 2x more 2,4-D ester volatilizes at 80 o than 70 o –Low humidity = more volatilization –Air Inversions
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Protecting Water Resources
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Protect your wells!
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Protecting Water Resources Practice IPM Environmental considerations Well Locations? Calibrate and use only what is needed Mix and load carefully Prevent back-siphoning Consider the weather Select, store and dispose of pesticides carefully
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