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?
