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Pesticide Properties

Pesticide Properties. soil surface. offsite. Runoff: movement of material away from application location over soil surface. Leaching: the downward movement of material into the soil profile with soil water. Factors Affecting Pesticide Runoff. Soil infiltration rate

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Pesticide Properties

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  1. PesticideProperties

  2. soil surface offsite Runoff: movement of material away from application location over soil surface

  3. Leaching: the downward movement of material into the soil profile with soil water

  4. Factors Affecting Pesticide Runoff • Soil infiltration rate • precipitation or irrigation rate is greater than what the soil or media can absorb • Pesticide solubility and/or adsorption characteristics • material may be carried off-site in runoff water or, if bound tightly to soil particles, it can be carried with sediment in runoff water

  5. Pesticide Properties • Solubility (ppm) • Adsorption (Koc) • Persistence or half-life (T1/2) • affected by biotic and abiotic factors • microbes • photodecomposition • pH • others

  6. Solubility • Amount of material that can be dissolved • Reported in ppm or mg/l (same thing) • The higher the number, the more soluble the herbicide • glyphosate (isopropyl amine salt) (Roundup) 900,000ppm • atrazine (Aatrex) 33ppm • oryzalin (Surflan) 3ppm

  7. Adsorption • The process by which a material associates with a surface (“stickiness”) • Reported as a Koc value • If pesticide is not adsorbed at all Koc=0 • Pesticides with a low Koc are more likely to leach all other things being equal

  8. General Classification for Koc Values • Koc>1,000= pesticide attaches strongly to soil; unlikely to move unless soil erosion occurs. • Koc< 500 tend to move with water; high potential to leach or move off-site with surface water runoff. • 500<Koc<1000 potential to move depends on other cultural or environmental factors.

  9. Adsorption • Soil organic matter and clay content will increase adsorption • Examples average Koc • glyphosate (isopropyl amine salt) (Roundup) 24,000 • atrazine (Attrex) 100 • oryzalin (Surflan) 600

  10. Pesticide Persistence

  11. Soil Properties • Texture proportions of sand, silt, and clay • Permeability how well water is absorbed • Organic Matter Content affects adsorption

  12. Organic component Organic Matter Lower Adsorption Higher Adsorption

  13. Scheduling • Most herbicide that is lost from runoff or leaching is at the first watering event • Apply only enough water to “activate” herbicide for 1st irrigation • Better to pulse water or subirrigate from Wilson et al. 1994

  14. Reducing Pesticide Leaching • USE IPM • Follow the label • Select pesticides which have a low solubility and high adsorption rate • Check irrigation systems for output and uniformity • Use drip or micro-sprinklers • Herbicides: For first irrigation after application apply only enough water to move herbicide to active zone

  15. Reducing Surface Runoff • Don’t overirrigate • Use vegetative buffer strips • Use as close a pot spacing as possible • Place containers on gravel or fabric

  16. Greatest Chance of Runoff • Pesticide • High adsorption (high Koc) • Persistent (long half-life) • Soil • Fine or easily eroded • High soil moisture • Management • Over-irrigation • Lack of filter strips or buffers • Nursery bed surface (gravel<fabric<plastic)

  17. Aquatic Toxicity • Select product with lowest toxicity to aquatic organisms • High LC50 (concentration that is lethal to 50% of tested population) • Usually in ppm • Acephate LC50 =730, Diazinon LC50 =0.09 (based on rainbow trout exposure)

  18. VISIT OUR WEB SITE www.ipm.ucdavis.edu

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