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Environmental Fate of Turfgrass Herbicides

Environmental Fate of Turfgrass Herbicides. Tim R. Murphy The University of Georgia Crop and Soil Sciences. Public Concerns. Health Quality of Life Environment Nuclear and Toxic Waste Chemicals vs. Natural Right-to-Know. Cause cancer Not well tested Harm animals Last forever.

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Environmental Fate of Turfgrass Herbicides

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  1. Environmental Fate of Turfgrass Herbicides Tim R. Murphy The University of Georgia Crop and Soil Sciences

  2. Public Concerns • Health • Quality of Life • Environment • Nuclear and Toxic Waste • Chemicals vs. Natural • Right-to-Know

  3. Cause cancer Not well tested Harm animals Last forever Not “natural” Used carelessly Contaminate water Any amount is dangerous “Public Concerns” About Chemicals

  4. Turf Herbicide Concerns • Last forever • Contaminate water • Affect human health • Sterilize soil • Use is not needed • Kill all desirable organisms • Degrade the environment

  5. “For the price of a green lawn, we are poisoning our children.” Family Circle magazine, 1991

  6. Fate of Herbicides Applied to Turf • Water solubility - the extent to which a pesticide will dissolve in water • Sorption by clay colloids and organic matter • Adsorption - binding of a herbicide to the surface of a soil particle . • Absorption- Penetrates into plant tissue • Microbial degradation - influenced by herbicide concentration, temperature, moisture, pH, oxygen, microbial population

  7. Fate of Herbicides Applied to Turf • Chemical degradation and photodecompositionHydrolysis, oxidation, reduction, and photodecomposition under field conditions • Volatilization and evaporation - Loss due to an increase in temperature, vapor pressure, and wind movement. • Plant uptake and metabolism -roots, shoots, leaves

  8. Environmental Fate of Herbicides

  9. Herbicide Fate in the Soil • Herbicide Chemical Characteristics • Soil Physical-Chemical Characteristics

  10. Herbicide-Chemical Properties • Ionic State (cation, anion, basic or acidic) • Water Solubility • Vapor pressure • Hydrophobic/hydrophilic • Partition coefficient • Chemical, photochemical, microbial sensitivity

  11. Soils - Solid Phase • Sand - 0.2 to 2.0 mm • Silt - 0.002 to 0.2 mm • Clay - < 0.002 • Organic matter - decaying plant and and animal residue

  12. Soils - Colloidal Phase • Consists of clay and organic matter • Huge surface area • Negatively charged • Anions (-charge) repelled • Cations (+charge) attracted • Primarily responsible for binding herbicides

  13. Soils - Gas & Liquid Phase • Gas - oxygen, carbon dioxide, others • Liquid - water (with dissolved molecules, ions, etc.)

  14. Soils - Living Phase • Microorganisms - bacteria, actinomycetes, fungi • Algae • Vertebrates and Invertebrates • Microorganisms degrade herbicides

  15. Microbial Degradation • Higher with high microbial populations • May use as food source, or just degrade the herbicide • Faster under warm, moist conditions • Slower under cool, dry conditions

  16. Herbicide Dissipation • Dosage • Affinity for binding • Water solubility, Leaching • Microbial and chemical degradation • Volatilization • Photodecomposition • Plant Uptake and Metabolism

  17. Herbicide Adsorption • Soil texture • coarse, sandy soils have few binding sites • Permeability • highly permeable soils low in CEC have few binding sites • Soil OM and clay content • increase binding • Excessive moisture interferes with binding

  18. Soil FactorsCation Exchange Capacity (CEC) • soils ability to adsorb positively charged compounds • fine-textured, high-organic matter soils have larger CEC’s than coarse, low-organic matter soils paraquat

  19. Soil FactorsOrganic Matter and Texture • most important for soil applied herbicides • Indirectly influences all processes that affect herbicides!! • the greater the organic matter and clay content, the greater adsorption of herbicides

  20. 5 4.5 4 3.5 3 Rate (kg/ha) 2.5 2 1.5 1 0.5 0 0.8 1.9 3.9 6.4 11 18 OM (%) Amount of atrazine required to reduce giant foxtail growth by 50% at varying OM levels. Parochetti 1973

  21. Water Movement • Surface runoff • Leaching • Capillary action

  22. Factors That Affect Leaching

  23. Relative Movement of Herbicides

  24. Mobility of Preemergence Herbicides in Soil

  25. Mobility of Postemergence Herbicides in Soil

  26. Volatility Volatility- physical change of a liquid or solid to gas.

  27. Volatility • Related to vapor pressure • Increases at high air temperatures • Increases under high soil moisture conditions • Higher on coarse textured, sandy soils

  28. Preemergence Herbicide Water Solubility and Relative Volatility

  29. Postemergence Herbicide Volatility

  30. Photodecomposition Photodecomposition- Breakdown of the herbicide by sunlight (primarily UV portion).

  31. Herbicide Persistence - Soil Usually expressed as the half-life (t1/2).

  32. Herbicide ½ Life Amount of time it takes a herbicide to reach one-half (t1/2) of the originally applied concentration. Expressed in days, wks, months, yrs.. 1.0 lb. Ai/acre0.5 lb. Ai/acre

  33. Preemergence Herbicides – Avg. t-1/2

  34. Preemergence Herbicides – Avg. t-1/2

  35. Postemergence Herbicides – Avg. t-1/2

  36. Postemergence Herbicides – Avg. t-1/2

  37. Postemergence Herbicides – Avg. t-1/2

  38. Herbicide Degradation

  39. Herbicide Persistence (75% degradation) B B B B E E E E E

  40. Herbicide Leaching Potential Index • HLP – developed by Warren and Weber, NCSU • Factors considered include: • Binding ability • Persistence (t-1/2) • Application rate • Amount that penetrates turf canopy and reaches soil • Soil pH, O.M., type

  41. HLP Index • Low potential for leaching - > 10.1 • Moderate potential - 1.0 to 10.0 • High potential - < 1.0

  42. HLP Index – Preemergence

  43. HLP Index – Postemergence

  44. Soil Leaching Potential - SLP • Texture, O.M. and pH have greatest impact on herbicide leaching • Clays retard movement, sands increase • High O.M. retards, low O.M. increases • Acidic pH increases degradation • Neutral to alkaline pH decreases degradation, and can increase movement potential

  45. SLP • S, LS, SL, L, SiL, L: 10 • SCL, CL, SiCL: 6 • SiC, SC: 3 • C or muck: 1 S= sand, L = loam, Si = silt, C = clay

  46. SLP • Can be calculated for each soil type • Based on texture and pH 0 to 91 cm • Based on O.M. in upper 15 cm • High soil leaching potential: > 131 • Moderate: 90 to 130 • Low: < 89

  47. Herbicide Selection with HLP/SLP Matrix

  48. Best Management Practices - BMPS • Use herbicides with low HLP Indices on high SLP soils • Train employees on proper application techniques • Spot treat if possible • Follow label • Be aware of any water advisory statements

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