Proceedings of the
2007 CPM Short Course and MCPR Trade Show
December 4 – 6, 2007
Minneapolis Convention Center
Do not Reproduce or Redistribute Without Written Consent of the Author(s)
Improving Glyphosate Performance
Calvin G. Messersmith
Professor Emeritus
Plant Sciences Department
North Dakota State University
Fargo, North Dakota USA
Acknowledgments
• Dr. Brad Ramsdale
– Nebraska College of Technical Agriculture-Curtis
• Dr. John Nalewaja
– Professor Emeritus, North Dakota State University
• Dr. Zenon Woznica
– Visiting Scientist, Poznan (Poland) Agricultural
University
• Dr. Jingkai Zhou
– Former Research Assoc., North Dakota State Univ.
Major factors affecting glyphosate
efficacy
• Chemical and physical characteristics of
glyphosate
– Water solubility
– Antagonistic cations in spray water and environment
• Application factors
– Spray volume
– Sprayer nozzles
– Adjuvants
• Ammonium sulfate
• Surfactants
Glyphosate acid
O
H
O
-
H
HO - C - CH2 - N - CH2 - P - OH
OH
• pKa – 1st phosphonic –
•
Carboxylate –
•
2nd phosphonic •
Amine -
0.8
2.3
6.0
11.0
+
Glyphosate acid
O
H
O
-
HO - C - CH2 - N - CH2 - P - OH
OH
• Sources of ions that affect glyphosate
– Glyphosate formulation
– Soil – many + and - charges
– Spray water – Ca+2, Mg+2, Na+
– Plant factors: surface Ca+2 , stress
H+
Water solubility of various salts
• Glyphosate salts
– Acid
– Ammonium
– Calcium
– Isopropylamine
– Potassium
– Sodium
160 g/L
300 g/L
30 g/L
500 g/L
900 g/L
500 g/L
Water solubility of various salts
• Glyphosate salts
– Acid
– Ammonium
– Calcium
– Isopropylamine
– Potassium
– Sodium
160 g/L
300 g/L
30 g/L
500 g/L
900 g/L
500 g/L
~1 lb/gal
3 lb/gal
4.5 lb/gal
Reaction of cations with glyphosate
K
O
H
O
HO - C - CH2- N - CH2- P - O
OH
CH3
+
H3KN - CH
+
CH3
+
Absorption of glyphosate by plants
Glyphosate salt
Acid
Isopropylamine
Ammonium
Sodium
Calcium
Potassium
LSD (0.05)
% 14C absorbed
49
59
44
18
1
?
5
Nalewaja, J.D., B.L. deVilliers, and R. Matysiak. 1996. Surfactant and salt
affect glyphosate retention and absorption. Weed Res. 36:245-247.
Solubility and absorption of glyphosate
Glyphosate salt
Solubility
% 14C absorbed
Acid
160 g/L
49
Isopropylamine
500 g/L
59
Ammonium
300 g/L
44
Sodium
500 g/L
18
Potassium
900 g/L
?
Calcium
30 g/L
1
LSD (0.05)
5
Reaction of cations with glyphosate
K
O
H
O
HO - C - CH2- N - CH2- P - O
OH
CH3
+
H3KN - CH
+
CH3
+
Glyphosate acid
O
H
O
-
HO - C - CH2 - N - CH2 - P - OH
OH
• Sources of ions that affect glyphosate
– Glyphosate formulation
– Soil – many + and - charges
– Spray water – Ca+2, Mg+2, Na+
– Plant factors: surface Ca+2, stress
H+
Glyphosate is adsorbed to soil
• Glyphosate is immediately inactivated
upon contact with soil (or dirty water)
• Glyphosate efficacy is reduced by dust on
weed leaves (Zhou et al. 2006. Weed Sci. 54:1132-1136)
Treatment
Plant without dust
Plant with dust
Control
81%
60%
Glyphosate acid
O
H
O
-
HO - C - CH2 - N - CH2 - P - OH
OH
• Sources of ions that affect glyphosate
– Glyphosate formulation
– Soil – many + and - charges
– Spray water – Ca+2, Mg+2, Na+
– Plant factors: surface Ca+2, stress
H+
Sources of cations in sprayer tanks
• Spray carrier water
– Ca+2; also other divalents cations - Mg+2, Fe+2
– Na+1; also other monovalent cations
• Adjuvants
– (NH4)2SO4 fertilizer
Glyphosate salts
– Isopropylamine+1, K+1, diammonium (2 NH4+)
Reaction of cations with glyphosate
Ca
2+
O
H
CH3
O
HO - C - CH2- N - CH2- P - O
+
H32N+ - CH
Ca
OH
CH3
+
CH - NH3
CH3
CH3
O
H
O
O - P - CH2- N - CH2- C - OH
OH
Glyphosate acid
O
H
O
-
HO - C - CH2 - N - CH2 - P - OH
OH
• Sources of ions that affect glyphosate
– Glyphosate formulation
– Soil – many + and - charges
– Spray water – Ca+2, Mg+2, Na+
– Plant factors: surface Ca+2, stress
H+
Water solubility of various salts
• Glyphosate salts
–
–
–
–
–
–
Acid
Ammonium
Calcium
Isopropylamine
Potassium
Sodium
160 g/L
300 g/L
30 g/L
500 g/L
900 g/L
500 g/L
• Other salts
–
–
–
–
Ammonium sulfate
Calcium sulfate
Potassium sulfate
Sodium sulfate
760 g/L
2 g/L
120 g/L
200 g/L
Spray deposit characteristics
Glyphosate concentration
Glyphosate was more phytotoxic when
applied in one concentrated drop than nine
dilute drops of equal size
Cranmer and Linscott
Weed Science 1990 and 1991
Spray deposit characteristics
Droplet Spread
Glyphosate absorption was greater with
adjuvants that left a pile deposit
Nalewaja and Matysiak
4th International Symposium on Adjuvants for Agrochemicals. 1995
Spray deposit characteristics
Spray Water Quality
Glyphosate- + IPA+ or K+
Ca++
Na+
Droplet
drying
Glyphosate – Ca
Low solubility & poor absorption
Glyphosate- + IPA+ or K+ or Na+
Spray deposit characteristics
(NH4)2SO4 Can Overcome Antagonism
Glyphosate- + IPA+ or K+
Ca++
Na+
2 NH4+ + SO4- Droplet
drying
CaSO4
Precipitates before glyphosate-Ca
Glyphosate- + NH4+ or IPA+ or K+ or Na+
Wheat leaf surface with residual of glyphosate
(source: Nalewaja et al., 1992)
Glyphosate +
Tween 20
Wheat leaf surface with residual of glyphosate
(source: Nalewaja et al., 1992)
Glyphosate + Tween 20
+ calcium chloride
Wheat leaf surface with residual of glyphosate
(source: Nalewaja et. al., 1992)
CaSO
4 crystal
CaSO
4
Glyphosate + Tween 20 +
calcium chloride +
ammonium sulfate
Plant stress affects glyphosate efficacy:
velvetleaf seedlings
Zhou et al. 2007. Weed Sci. 55:240-244
Source
of stress
None
Percent control
No adjuvant
84
Surf. & AMS
93
Cold
68
80
Drought
46
67
Flooding
50
68
Objective
• To evaluate the potential to reduce glyphosate
rates by decreasing spray volume
• To evaluate relationships among spray volume,
adjuvants, formulations, spray water quality,
and sprayer nozzles for glyphosate efficacy
Reasons for using very low herbicide
rates in experiments
The herbicide rate selected should provide control on the linear portion
of the bioassay curve between about 30% and 70% control
70%
Control %
•
30%
Herbicide rate
Herbicide Treatment 2
Herbicide Treatment 1
Diagram of three-species treatments
Wheat
Oat
Barley
Herbicide Efficacy Research
- Reduced herbicide rates
- Solid seeded assay species
- wheat, barley, oat, proso millet
- All-terrain-vehicle (ATV) sprayer
Experimental Design
- Randomized complete block
- 4 replicates
- Multiple years or locations
- Control evaluated visually
Spray water quality of two sources
CaCO3
Ca++
Mg++
Na+
K+
Soft
Hard
------ mg/L -----110
1550
30
230
8
238
59
146
6
51
Glyphosate with hard water
Roundup Custom® + 0.5% oxysorbic surfactant
100
% control
90
80
70
LSD (0.05) = 9
60
50
40
30
20
10
0
0.5 oz/A
1.0 oz/A
2.0 oz/A
Glyphosate Rate
No AMS
0.5% w/v
1% w/v
Combined over 2 years and 3 grass species
2% w/v
Conclusions from previous slide
• Ammonium sulfate at 0.5% w/v was sufficient to
overcome the antagonism from Ca and other
ions
• Efficacy of glyphosate at low rates in hard water
is enhanced by adding ammonium sulfate
– Ca+2 is precipitated as CaSO4
– Glyphosate-NH4 is an effective herbicide
• Glyphosate at high rates in hard water includes
enough glyphosate to allow some
(glyphosate)2Ca to form and still have extra
glyphosate to provide adequate control
Glyphosate with soft water
Roundup Custom® + 0.5% oxysorbic surfactant
100
90
80
LSD (0.05) = 7
% control
70
60
50
40
30
20
10
0
0.5 oz/A
1.0 oz/A
2.0 oz/A
Glyphosate Rate
No AMS
0.5% w/v
1% w/v
Combined over 2 years and 3 grass species
2% w/v
Conclusions from previous slide
• Efficacy of glyphosate at very low rates in
soft water is enhanced slightly by adding
ammonium sulfate at 0.5% w/v, but the
commercial formulation contains adequate
glyphosate and surfactant to optimize
glyphosate efficacy at medium to high
glyphosate rates
• Ammonium sulfate at 2% w/v may be
slightly antagonistic at low spray volumes
in soft water
Spray volume - Grass species
% control
Roundup Ultra® + 0.5% v/v surfactant
100
90
80
70
60
50
40
30
20
10
0
LSD (0.05) = 11
2.0 oz/A
2.5 gal/A
1.0 oz/A
5 gal/A
10 gal/A
0.5 oz/A
20 gal/A
Combined over oat and wheat, 1 location
Conclusions from the previous slide
• Efficacy of glyphosate at all rates that provide
less than complete control is greatest at very low
spray volumes (2.5 to 5 gal/A)
• Glyphosate efficacy is reduced at spray volumes
above about 5 gal/A
• Glyphosate rates may be reduced by about 1/3
at low spray volumes
• Probably glyphosate efficacy in higher spray
volumes is reduced because the glyphosate and
surfactant concentration in the spray droplet is
too diluted for optimum efficacy
Glyphosate and surfactant
concentrations
Spray volume
Glyphosate rate
2.5 gal/A 5 gal/A
10 gal/A
20 gal/A
(relative Glyp and surf. concentration)
2 oz/A
8x
4x
2x
1x
1 oz/A
4x
2x
1x
0.5x
0.5 oz/A
2x
1x
0.5x
0.25x
Efficacy vs. relative Glyp and surf. concentration: r = 0.83
Thus, glyphosate efficacy is greatest when the glyphosate
and surfactant concentration in the spray droplet is high
Spray Volume – Quackgrass (Elytrigia repens)
% quackgrass control
Roundup UltraMAX®
100
90
80
70
60
50
40
30
20
10
0
LSD (0.05) = 10
6 oz/A
5 gal/A
3 oz/A
10 gal/A
1.5 oz/A
20 gal/A
Combined over 2 years and treatments +/- NIS
Conclusions from the previous slide
• Efficacy of glyphosate at all rates that
provide less than complete control is
greatest at the lowest spray volume of 5
gal/A and was reduced by higher spray
volumes
• Probably glyphosate efficacy in higher
spray volumes is reduced because the
glyphosate and surfactant concentration in
the spray droplet is too diluted for optimum
efficacy
Glyphosate and surfactant
concentrations on quackgrass
Spray volume
Glyphosate rate
5 gal/A
10 gal/A
20 gal/A
(relative Glyp and surf. concentration)
6 oz/A
24x
12x
6x
3 oz/A
12x
6x
3x
1.5 oz/A
6x
3x
1.5x
Efficacy vs. relative Glyp and surf. concentration: r = 0.76
Commercial formulations
Glyphosate applied at 1 oz/A
100
LSD (0.05) = 8
90
80
Control (%)
70
60
50
40
30
20
10
0
None
AMS (1% w/v)
2.5 gal/A
None
AMS (1% w/v)
10 gal/A
Roundup Custom + NIS
Roundup Ultra
Glyphomax Plus
Glyfos X-tra
Touchdown
Roundup UltraDry
Combined over grass species and locations
Pre-orifice
Drift Guard
Spraying Systems Inc.
Recommended spray
pressures: 30 to 60 psi
Turbo TeeJet
Spraying Systems Inc.
Pre-orifice
Recommended spray pressures: 15 to 90 psi
Air-induction
(venturi) nozzles
Venturi
Air-induction
Large
exit tip
Sprayer Nozzles
% control
Glyphosate (Roundup Ultra®) at 1 oz/A
100
90
80
70
60
50
40
30
20
10
0
LSD (0.05) = 8
2.5 gal/A
Standard
TurboDrop
10 gal/A
Turbo TeeJet
Ultra-Lo-Drift
Combined over grass species and environments
Summary
• AMS at 0.5% w/v was sufficient for hard water
sources at low spray volumes
– AMS at 2% w/v may be slightly antagonistic at low
spray volumes and without antagonistic salts
• Glyphosate efficacy was greatest at spray
volumes of 2.5 or 5 gal/A.
– Rates may be reduced by 1/3 at low spray volumes
– Advantages include high glyphosate concentration
that increased absorption, overcoming antagonistic
salts, and higher concentrations of surfactant in
commercial formulations
Summary
• Commercial formulations of glyphosate that
contain surfactant provided similar grass control
• Glyphosate efficacy was similar for several driftreducing nozzles and a standard flat-fan nozzle
The bottom line
• Use clean spray water and an adequate
rate of glyphosate
• Use as low a rate of application (gal/A) as
is practical
• Add ammonium sulfate at 0.5% w/v in
most cases
• Add nonionic surfactant when glyphosate
rates are very low or spray volumes are
high
• Spray non-stressed plants, when possible
Application of these concepts to other
herbicides, especially weak acid herbicides
• Other weak acid herbicides, e.g., 2,4-D,
dicamba, MCPA,…are antagonized by cations
like Ca+2 and Na+1
• Ammonium sulfate is an adjuvant that can
overcome antagonism of cations with other weak
acid herbicides
• Most postemergence herbicides are most
effective at very low application volumes
• Most postemergence herbicides are equally
effective when applied with conventional and
drift-reducing nozzles, even at very low
application volumes
Research supported by
USDA-CSREES grants
under agreements 97-34361-3960,
98-34361-6831, and 99-34361-8432.