Reeves Petroff Pesticide Education Specialist Montana State University Extension

How Chemicals Move Through Soil A Review How Water Moves Through Soil

Pesticide Characteristics Chemical characteristics of a pesticide will determine how it behaves in the environment. Four main characteristics: –Solubility –Adsorption –Half-life (aka. Persistence) –Volatility

Solubility Amount of chemical dissolved into a solution PPM > 30 ppm = high tendency to leach or runoff. Tordon = ,4-D = 890 Assert = 1370 Ally/Escort –1750 (pH 5) – 2790 (pH 7) –213,000 (pH 9) Paraquat = 7000 Roundup = 12,000 Which is the higher solubility? 50 or 500 ppm? 500 ppm Water soluble pesticides can move easily with water

Most lower solubility pesticides will bind more readily to clay and OM than those with higher solubility.

Pesticides in the Environment Environmental Fate of

What is Pesticide Environmental Fate? How and where a pesticide enters the environment How long it lasts Where it goes. BIOAVAILABILTY BIOCONCENTRATION BIOMAGNIFICATION

Fate Processes

Pesticide Losses at Application Method of application Rate Timing Number of applications Placement

Adsorption The binding of a pesticide molecule to a soil particle Clay & Organic matter!! More organic matter = more binding

Measuring Adsorptivity - K oc K oc Organic carbon partition coefficient - universal index How tightly a pesticide will bind to the organic matter in the soil.

Wet soils limit adsorption. Cool & dry is best for highly water soluble pesticides

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 Methyl Parathion – 5100 Lorsban Treflan – 7000 Roundup – 24,000 Buctril – 10,000 Capture – 216,500 Paraquat – 1,000,000

Runoff vs. Leaching

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. Point vs. Non-point contamination

Soil texture has a big influence on leaching of pesticides

More adsorptive

Even a jar test will give you an idea!

Gravity has more influence on leaching in saturated soils In dry soils, capillary action influences movement

Degradation –Microbes near soil surface – more O 2 and nutrients –pH –Sunlight –Rate applied Expressed as “half-life.” Time required to degrade 50% of existing concentration Persistence (Residual)

Malathion - 1 2,4-D - 10 Banvel – 14 Ally, Amber – 30 Stinger - 40 Assert – 45 Roundup - 47 Tordon – 180 Spike Paraquat – 1000 Degradation values of some common pesticides (1/2 life in days)

Pesticide Drift Physical drift caused by small droplets –Improper nozzles –Improper pressure Chemical drift –Volatilization

Volatility Conversion of a liquid or solid to a gas Lower vapor pressure = lower volatility 2,4-D ester = high Banvel = high Banvel SGF = moderate Tordon = low Roundup = low

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

Protecting Water Resources

Protect Sensitive Areas! Aerial Spraying100 feet Vehicle Spraying 25 feet Hand Application 10 feet

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

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

Drift

Why Interest in Drift? Spotty Pest Control Wasted chemicals Off-target damage Higher costs - $$$ Environmental impact –Water and Air Quality Public more aware of pesticide concerns! (Negative) Spraying in more populated areas? (Suburbs)

Applicator Nozzle

WHAT IS DRIFT? Movement of.. spray particles vapors off-target Less effective control Possible injury to susceptible vegetation and wildlife.

DRIFT POTENTIAL BOOM HEIGHT HIGH PRESSURE SMALL DROPLETS Drift Production Movement

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

Driftability of Spray Droplets of Varying Sizes 10 feet 3 mph 20  20  50  50  100  150   8 ft 22 ft. 48 ft. 178 ft ft. 8 ft 22 ft. 48 ft. 178 ft ft. \ HEIGHT OF SPRAY NOZZLES ABOVE TREATED SURFACES

Nozzle Drop Size Classes Very Fine to Fine < 200 um Medium to Coarse – 200 to 450 um Very Coarse > 450 um

80 means 80 o fan 03 means 0.3 gallons per minute at 40 psi (38 ½ ounces per minute) 8003 tip

87% reduction in drift prone droplets < 150 microns Low drift 0.2 gal/min flow rate - 40 psi Compared to 8002 Standard Flat-fan nozzle Low Drift Nozzles

Tip Spray Selection by Drop Size Turbo TeeJet Flat-fan

äTemperature & humidity ä Air movement (direction and velocity) äAir stability/inversions äTopography Weather and Other Factors Affecting Drift

Evaporation of Droplets Wind High Relative Humidity Low Temperature Low Relative Humidity High Temperature Fall Distance

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) < *Conditions assumed: 90 F, 36% R.H., 25 psi., 3.75% pesticide solution 7 seconds for a 100 micron size droplet to evaporate at 90 o F at 36% RH

Strategies to Reduce Drift Avoid adverse weather conditions 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

Shielded Sprayers