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Environmental Fate of Turfgrass Herbicides

Tim R. Murphy
The University of Georgia
Crop and Soil Sciences

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TABLE OF CONTENTS

Environmental Fate of Turfgrass Herbicides Public Concerns "Public Concerns" About Chemicals Turf Herbicide Concerns Family Circle Magazine Quote Theoretical Rate Needed for Weed Control Fate of Herbicides Applied to Turf Fate of Herbicides Applied to Turf Environmental Fate of Herbicides Herbicide Fate in the Soil Herbicide-Chemical Properties Soils - Solid Phase Soils - Colloidal Phase Soils - Gas & Liquid Phase Soils - Living Phase Microbial Degradation Herbicide Dissipation Herbicide Adsorption Soil Factors: Cation Exchange Capacity (CEC) Herbicide Particles in Soil Soil Factors: Organic Matter and Texture Amount of atrazine required to reduce giant foxtail growth by 50% at varying OM levels. Water Movement Factors That Affect Leaching Relative Movement of Herbicides Mobility of Preemergence Herbicides in Soil Mobility of Postemergence Herbicides in Soil Volatility Volatility Preemergence Herbicide Water Solubility and Relative Volatility Postemergence Herbicide Volatility Photodecomposition Herbicide Persistence - Soil Herbicide 1/2 Life Preemergence Herbicides - Avg. t-1/2 Preemergence Herbicides - Avg. t-1/2 Postemergence Herbicides - Avg. t-1/2 Postemergence Herbicides - Avg. t-1/2 Postemergence Herbicides - Avg. t-1/2 Herbicide Degradation Herbicide Persistence (75% degradation) Herbicide Leaching Potential Index HLP Index HLP Index - Preemergence HLP Index - Postemergence Soil Leaching Potential - SLP SLP SLP Herbicide Selection with HLP/SLP Matrix Best Management Practices - BMPS BMPS (continued) SU Herbicide Lateral Movement SU Herbicide Lateral Movement SU Herbicide Lateral Movement SU Herbicide Lateral Movement SU Herbicide Lateral Movement Kerb Can SU Herbicides Move? 0 Residue Ain’t Possible!!! Risk Communication Facts georgiaturf.com

SLIDE CONTENTS

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 “Public Concerns” About Chemicals Cause cancer Not well tested Harm animals Last forever Not “natural” Used carelessly Contaminate water Any amount is dangerous Turf Herbicide Concerns Last forever Contaminate water Affect human health Sterilize soil Use is not needed Kill all desirable organisms Degrade the environment “For the price of a green lawn, we are poisoning our children.” Family Circle magazine, 1991 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 Fate of Herbicides Applied to Turf Chemical degradation and photodecomposition Hydrolysis, 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 Environmental Fate of Herbicides Herbicide Fate in the Soil Herbicide Chemical Characteristics Soil Physical-Chemical Characteristics Herbicide-Chemical Properties Ionic State (cation, anion, basic or acidic) Water Solubility Vapor pressure Hydrophobic/hydrophilic Partition coefficient Chemical, photochemical, microbial sensitivity 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 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 Soils - Gas & Liquid Phase Gas - oxygen, carbon dioxide, others Liquid - water (with dissolved molecules, ions, etc.) Soils - Living Phase Microorganisms - bacteria, actinomycetes, fungi Algae Vertebrates and Invertebrates Microorganisms degrade herbicides 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 Herbicide Dissipation Dosage Affinity for binding Water solubility, Leaching Microbial and chemical degradation Volatilization Photodecomposition Plant Uptake and Metabolism 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 Soil Factors Cation 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 Soil Factors Organic 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 Amount of atrazine required to reduce giant foxtail growth by 50% at varying OM levels. Parochetti 1973 Water Movement Surface runoff Leaching Capillary action Factors That Affect Leaching Relative Movement of Herbicides Mobility of Preemergence Herbicides in Soil Mobility of Postemergence Herbicides in Soil Volatility Volatility - physical change of a liquid or solid to gas. Volatility Related to vapor pressure Increases at high air temperatures Increases under high soil moisture conditions Higher on coarse textured, sandy soils Preemergence Herbicide Water Solubility and Relative Volatility Postemergence Herbicide Volatility Photodecomposition Photodecomposition - Breakdown of the herbicide by sunlight (primarily UV portion). Herbicide Persistence - Soil Usually expressed as the half-life (t1/2). 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/acre 0.5 lb. Ai/acre Preemergence Herbicides – Avg. t-1/2 Preemergence Herbicides – Avg. t-1/2 Postemergence Herbicides – Avg. t-1/2 Postemergence Herbicides – Avg. t-1/2 Postemergence Herbicides – Avg. t-1/2 Herbicide Degradation Herbicide Persistence (75% degradation) E E E E B B B B E 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 HLP Index Low potential for leaching - > 10.1 Moderate potential - 1.0 to 10.0 High potential - < 1.0 HLP Index – Preemergence HLP Index – Postemergence 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 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 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 Herbicide Selection with HLP/SLP Matrix 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 BMPS (continued) Consider mixing/loading pads, with spill containment Do not mix or apply within 100 ft. of a well head Prevent back-siphoning Calibrate sprayer Establish buffer (non-treated areas) SU Herbicide Lateral Movement Griffin, GA Lateral runoff facility 5% uniform slope Wobbler irrigation heads 1.25 inches per hour Tifway bermudagrass 0.5 inch clip height SU Herbicide Lateral Movement Plots 25 ft. long Lower 10 ft. fall-seeded with perennial ryegrass Upper 15 ft. not overseeded January 22, 2004, applied to dormant bermuda Monument at 0.33 and 0.56 oz./acre Manor at 0.5 oz./acre TranXit at 2.0 oz./acre Kerb at 2.0 lbs./acre SU Herbicide Lateral Movement Before application Applied 2.5 inches irrigation (2 hrs), 37% saturation Waited ~ 1hr, until foliage dried Applied herbicides Waited ~ 1hr, until foliage dried Applied 2.5 inches irrigation (2 hrs) Applied 0.5 inch irrigation water 24 HAT SU Herbicide Lateral Movement WHAT HAPPENED?? Kerb – moved 8 ft. (76% injury) Monument 0.33 oz. – 0.7 ft (3%) Monument 0.56 oz. – 3 ft. (14%) Manor 0.5 oz. – 0.7 ft. (1) TranXit 2.0 oz – 0.6 ft. (1) NOTE: No significant injury occurred until 48 DAT KERB Kerb Great for Poa Hell on ryegrass Can SU Herbicides Move? Yes, if: Surface film of water present at application Irrigation or rainfall immediately after application Not watering after foliage has dried Dew re-suspends and can cause tracking (prevent by watering in) Improperly adjusted irrigation heads 0 Residue Ain’t Possible!!! 1 ppm = one second in 12 days 1 ppb = one second in 32 years 1 ppt = one second in 32,000 years 1 ppq = one second in 32,000,000 years 1.0 lb. Ai/acre = 1.0 ppm in upper 3 inches Risk Communication “Everything is Poison. There is nothing without poisonous properties. The dose differentiates a remedy from a poison.” Philippus Aureolus Theophrastus Bombastus von Hohenheim 1493-1541 Better known a Paracelsus Facts 30 yrs added to lifespan in 20th century 8 yrs added since use of pesticides only 37% of land farmed in 1950 is cultivated today Dennis Avery, Hudson Institute, Wall Street Journal, August 12, 1999 deer, turkey, geese populations increasing in GA Thank you very much!! georgiaturf.com