University of Tennessee

Dr Tom Mueller

2019 IFCA Convention

January 28, 2019

Peoria, IL

Environmental Fate of Herbicides and

Atrazine Degradation in Illinois

Most of the soils from Illinois used

in this research

were provided by Mark Bernards,

Western Illinois University

Disclaimer• Views and Ideas expressed in this presentation do not

represent the views of the University of Tennessee

• Mention of a product does not constitute endorsement of that product to the exclusion of other similar products

Outline of talk (30 minutes only)• Introduction

• Adsorption

• Degradation Processes• Chemical• Biological

• Factors affecting biological degradation

• Quantifying degradation

• Leaching, surface runoff (not covered, due to brevity)

• Enhanced Atrazine degradation in IL soils

• Questions (if time is available)

4

Thomas C Mueller

Department of Plant Sciences

University of Tennessee

Knoxville, TN

Some slides used courtesy of Dr.

Scott Senseman

Herbicide Behavior in Soils

5

Introduction

• Farmers do not like to use PREs• Rainfall needed to activate

• If persistent, can reduce flexibility in crops

• Cost more money, but do not always work

• But, using PREs targets the weeds at their most vulnerable growth stage (germination)

• Some PREs have no confirmed resistance (yet)

Herbicide Adsorption to Soil• Adsorption

• Factors that affect adsorption

• What is a Kd?• Memorable demonstration

• CEC factors

Chemical and Biological Degradation

• Terminology• Degradation – Breakdown of an organic compound

• Metabolites – Degradation products formed as a result of metabolic functions

• Sometimes called “daughter” metabolites…

• Important in product registrations….

8

Biological Degradation• Dominant mechanism for degradation

• Involves microbial organisms (microbes) possessing enzymes that catalyze chemical reactions

• Microorganisms• Bacteria – Most numerous

• Actinomycetes – 5 to 20% of total bacteria

• Fungi – Less numerous

• Other – Plants, vertebrates, invertebrates

9Adapted from Paul and Clark, 1989.

Factors Affecting Biological DegradationTemperature

10Paul and Clark, 1989.

Factors Affecting Biological DegradationMoisture

11Paul and Clark, 1989.

Quantifying Degradation

12

Take your observed

data and get a half-

life or DT 50

Bigger number

means herbicide

lasts longer

IL1

Days after Treament

0 10 20 30 40

Atr

azin

e in s

oil

(pp

b)

0

500

1000

1500

2000

2500

DT50 = 12.7

What is Slow or Fast Degradation?

• Very Short < 5 days

• Short - 10 to 30 days

• Moderate - 30 to 90 days

• Long – 90 to 180 days

• Very long > 180 days

13

Based on J.B. Weber. 1993.

Herbicide degradation comments

• “New” EPA registrations usually require “short” herbicide half-life

• Carryover issues more pronounced in northern climates (frozen soils over winter)

• Major environmental factor that changes year to year is soil moisture

• Drought can increase persistence

Herbicide leaching

Herbicide leaching

• For weed control, a small amount of “leaching” is often needed for weed control

• Factors affecting leaching into soil depths• A. heavy rainfall soon after application

• B. low CEC soil

• C. high water solubility of herbicide

Herbicide Surface Runoff

• Factors affecting herb runoff• A. heavy rainfall soon after application

• B. sloping topography

• C. high soil erosion (herbicide moves with soil)

• D. higher herbicide use rates

Herbicide in Soils

• Farmers do not like to use PREs• Rainfall needed to activate

• If persistent, can reduce flexibility in crops

• Cost more money, but do not always work

• But, using PREs targets the weeds at their most vulnerable growth stage (germination)

• Some PREs have no confirmed resistance (yet)

Herbicide in Soils

•Questions?

A national survey of the effect of previous atrazine use on enhanced

atrazine degradation in US soils •Thomas C. Mueller

•University of Tennessee, USA

Thanks from Mueller

Alinna Umphres Ethan Parker

Cooperating States• 16 states

Soil Processing• Catalogued in upon receipt

• Stored at ~4C until use

• Soils saturated, allowed to drain

• ~ 5 g placed into 20 mL vials

• Each subsample fortified with atrazine in water

• Allowed to statically equilibrate at 22C

• -1, 0, 3, 7, 14, 21, 28, 42 DAT

Champaign County

Top graph has > 5 years history of atrazine use

bottom graph has no atrazine use

IL12

Days after Treament

0 10 20 30 40

Atr

azin

e in

so

il (p

pb

)

0

500

1000

1500

2000

2500

DT50 = 3.4

IL13

Days after Treament

0 10 20 30 40

Atr

azin

e in

so

il (p

pb

)

0

500

1000

1500

2000

2500

DT50 = 26.9

Carroll County

IL14

Days after Treament

0 10 20 30 40

Atr

azin

e in s

oil

(pp

b)

0

500

1000

1500

2000

2500

DT50 = 17.8

IL15

Days after Treament

0 10 20 30 40

Atr

azin

e in s

oil

(pp

b)

0

500

1000

1500

2000

2500

DT50 = 2.9

McDonough/Henderson County

IL16

Days after Treament

0 10 20 30 40

Atr

azin

e in

so

il (p

pb

)

0

500

1000

1500

2000

2500

DT50 = 11.6

IL11

Days after Treament

0 10 20 30 40

Atr

azin

e in s

oil

(pp

b)

0

500

1000

1500

2000

2500

DT50 = 2.1

Pike County

IL10

Days after Treament

0 10 20 30 40

Atr

azin

e in s

oil

(pp

b)

0

500

1000

1500

2000

2500

DT50 = 1.6

IL9

Days after Treament

0 10 20 30 40

Atr

azin

e in s

oil

(pp

b)

0

500

1000

1500

2000

2500

DT50 = 0.7

Douglas County

IL8

Days after Treament

0 10 20 30 40

Atr

azin

e in s

oil

(pp

b)

0

500

1000

1500

2000

2500

DT50 = 20.3

IL7

Days after Treament

0 10 20 30 40

Atr

azin

e in s

oil

(pp

b)

0

500

1000

1500

2000

2500

DT50 = 5.2

Washington County

NoHisDT50/HisDT50 =Enhancement Factor (EF)

IL1

Days after Treament

0 10 20 30 40

Atr

azin

e in

so

il (p

pb

)

0

500

1000

1500

2000

2500

DT50 = 12.7

IL 2

Days after Treament

0 10 20 30 40

Atr

azin

e in

so

il (p

pb

)

0

500

1000

1500

2000

2500

DT50 = 0.8

EF <1.7

EF 1.7-3.5

EF >3.5

Soil Sample Sites

Concluding Thoughts

➢Using atrazine many times reduces its

persistence in soil

➢Weed control from atrazine residual

expected to be less

➢POST atrazine still effective

➢Add tank-mix partners

Concluding thoughts

➢PREs must be used.

➢No rainfall, no PRE activity

Acknowledgments• This research was largely funded by the Tennessee Ag

Experiment Station

• Technical assistance by Alinna Umphres and Ethan Parker and several student workers

• Always read and follow all label instructions for all crop protection products

August 5-8, 2019

Fort Collins, CO

Lory Student Center

Colorado State University

Fort Collins, CO 80523-8033

970-491-0229

Sponsored byTennessee Weed Science

Society

Tennessee Weed Science Short Course On Herbicide Modes of Action

and Resistance in WeedsIn Colorado

www.tnwss.org

2019 TN short course Speakers

Steve Duke,USDA-ARS

Dale L. ShanerTodd A. Gaines , Colorado State University.

Patrick J. Tranel, University of Illinois

Franck Dayan, Colorado State University

Peter Sikkema,University of Guelph

Questions?