Getting the Most Out of
Glyphosate
Dallas Peterson
Department of Agronomy
K-State Research & Extension
Glyphosate Issues
Product Confusion & Appropriate Rates
Factors that Affect Performance
AMS Requirements and Replacement Products
Application Timing and Yield Protection
Expanded Crop Uses
Weed Shifts and Glyphosate Resistant Weeds
New Glyphosate Products
Many glyphosate products
Different concentrations, formulations, and adjuvant
requirements
Need to read labels carefully and follow rate and
adjuvant recommendations
KSU research: few or no differences among most
glyphosate products when applied at same acid
equivalent rates and with recommended adjuvants.
Active Ingredient (a.i.)
vs. Acid Equivalent (a.e.)
Glyphosate acid is the active form of glyphosate in plants.
Nearly all glyphosate products formulated as salts, ie.
isopropylamine (IPA), diammonium (DA), or potassium (K).
Salt portions of formulated molecules have different weights.
Active ingredient weight includes the salt part of the molecule,
while acid equivalent weight does not.
Acid equivalent weight provides a better comparison of the
herbicidal component of the different glyphosate salts.
Glyphosate Products
Trade name
Salt
lb ai/gal
lb ae/gal 0.75 lb ae/A
Roundup Original
IPA
4
3
1 qt
Roundup Original MAX
K
5.5
4.5
22 oz
Roundup WEATHERMAX
K
5.5
4.5
22 oz
Touchdown
DA
3.75
3
1 qt
Touchdown Total
K
5
4.2
24 oz
Touchdown HiTech
K
6
5
19 oz
Durango
IPA
5.4
4
26 oz
Glyphomax XRT
IPA
5.4
4
26 oz
Most Generics
IPA
4
3
1qt
Surfactant Requirements with Glyphosate
Some glyphosate products always recommend using
surfactant, some indicate the addition of surfactant
is optional, while other products do not need
additional surfactant.
READ THE LABEL.
KSU generally recommends adding a source of
ammonium sulfate to all glyphosate applications, to
condition the water carrier.
Application Factors
Environment
ƒ
ƒ
ƒ
Temperature
Humidity
Drought Stress
Rainfree Interval
Time of Day
Spray Volume
Water Quality
Water Conditioners
Dust
Wheel Tracks
Roundup Application Time of Day
Material and Methods
Roundup rate: 1 pt/A
Application Stages:
P:
¾ LP:
¾
4-8 inch velvetleaf and Palmer amaranth
6-12 inch velvetleaf and Palmer amaranth
Application time of day:
¾
6 am, 10 am, 1:30 pm, 5 pm, 9 pm
The influence of application time of day on
Roundup performance, Manhattan, KS, 1999.
Application
Time of Day
6:00 am
10:00 am
1:30 pm
5:00 pm
9:00 pm
LSD
Palmer amaranth
Velvetleaf
Post
LP
Post
LP
--------------(% control)------------96
99
100
100
99
85
100
100
99
88
3
96
99
99
97
95
47
99
99
97
47
9
Late Postemergence - 6 am
Late Postemergence - 10 am
Late Postemergence - 9 pm
Application Time of Day
Weed control with Roundup was less when
applied pre-dawn or post sundown than during
the middle of the day.
Possible reasons:
presence of dew
¾ light influence on physiological interactions
¾ plant leaf orientation
¾
Leaf Orientation During the day and at Night
Velvetleaf
Day:
Night:
Palmer amaranth
5 gpa
10 gpa
20 gpa
Late postemergence glyphosate applied with spray volumes of 5,
10, and 20 gpa, Manhattan, KS 2000.
Oat control 2 WAT with a reduced rate of
glyphosate as influenced by spray volume,
Manhattan, KS 2001.
100
LSD=5
% Control
80
60
40
20
0
5 gpa
10 gpa
Spray Volume
20 gpa
AMS with Glyphosate in Soft Water
Without AMS
With AMS
AMS Replacements with Glyphosate in Hard Water
5% v/v Liquid AMS
(2% w/w, or 17 lb/100gal)
0.5% v/v
AMS Replacement
AMS
Replacements
with
Glyphosate
AMS Replacements with Glyphosate
Materials & Methods
Spray Volume: 15 gpa
Water Hardness: 103 Total Hardness as CaCO3
~6 grains/gal
Application: 7/12/05, 89F, 55% RH
¾
Velvetleaf:
6-12”
5-10 leaf
¾
Sorghum:
16”
V6
¾
Corn:
20”
V6
¾
Sunflower:
12-16”
8-10 leaf
Weed control with glyphosate plus AMS replacement
adjuvants at 4 WAT, Manhattan, KS (MS200508).
Treatment
Rate
Roundup WMax +:
8 oz +:
None
AMS
2 % w/w
Class Act NG
2.5% v/v
Alliance
1.25% v/v
Choice
0.5% v/v
Request
0.5% v/v
Speedway
0.5% v/v
Blendmaster
1% v/v
US 500
0.25% v/v
Citron
2.2 lb/100G
N-Tank
0.5% v/v
LSD (10%)
VelvetSunLeaf
Sorghum Corn
flower
---------------(% control)-------------40
77
72
65
30
37
42
43
33
37
62
7
60
90
90
83
47
58
50
57
50
40
68
9
52
83
82
77
42
50
50
53
47
40
67
7
73
92
90
90
60
75
85
80
70
78
90
7
Weed control with glyphosate as influenced by AMS
No AMS
17 lb AMS/100 Gal
Low Rate AMS
Replacement
Weed control with glyphosate plus AMS replacement
adjuvants at 4 WAT, Manhattan, KS , 2006 (MS200606).
Treatment
Rate
Roundup WMax +:
8 oz +:
None
AMS
2 % w/w
Class Act NG
2.5% v/v
Alliance
1.25% v/v
Choice WM
0.5% v/v
Request
0.5% v/v
Flame
0.5% v/v
Cayuse Plus
0.5% v/v
Loadout
0.5% v/v
Citron
2.2 lb/100G
N-Tank
0.5% v/v
LSD (10%)
VelvetSunLeaf
Sorghum Corn
flower
---------------(% control)-------------0
50
30
17
3
8
5
10
3
3
30
10
0
67
73
57
0
0
2
5
3
3
22
9
0
70
68
57
0
7
3
3
3
5
37
10
3
85
78
43
5
7
10
7
7
3
23
11
Weed control with glyphosate plus AMS replacement
adjuvants at 9 DAT, Tribune, KS 2006 (0613Fall).
Treatment
Roundup WMax +:
None
AMS
Class Act NG
Alliance
Choice WM
Request
Flame
Cayuse Plus
Loadout
Citron
N-Tank
LSD (10%)
Rate
Sorghum Corn Sunflower
---------(% control)----------
8 oz +:
2 % w/w
2.5% v/v
1.25% v/v
0.5% v/v
0.5% v/v
0.5% v/v
0.5% v/v
0.5% v/v
2.2 lb/100G
0.5% v/v
56
83
80
83
63
60
69
69
68
69
83
16
74
90
87
78
69
73
84
86
78
80
86
11
84
89
90
90
85
85
86
86
86
86
87
5
Applicator Tracks
Glyphosate + AMS
Low Rate
Full Rate
Weed Control and Yield Protection
Weed Pressure
Weed Control Strategy
Timing of Weed Control
Level of Weed Control
Late Roundup Application
Late Roundup Application
Late Roundup Application
Early season weed competition with soybeans.
Glyphosate
4 WAP
Soybean yield as influenced by time of weed removal, 1998.
(Peterson&Regehr)
Soybean yield (Bu/A)
35
Glyphosate, sequential
30
Glyphosate, single
25
20
15
10
5
0
Weed Free
22 DAP
27 DAP
31 DAP
35 DAP
No Removal
Herbicide Application Timing (Days after Planting)
V1/<4”
V2/<12”
V4/<24”
Soybean Stage /Weed Size
V5/<30”
Critical Period of Weed Control
Growth Stage or critical period to remove weeds
from a crop before significant yield loss occurs.
Highly variable and dependent on:
Weed Species Present
¾ Weed Populations
¾ Time of Weed Emergence Relative to Crop Emergence
¾ Crop Management Practices
– fertility, row spacing, population, etc
¾ Environmental Conditions
¾
Often 3 to 4 WAP with heavy weed pressure
Hard to Control Weeds with Glyphosate
Naturally Tolerant Species:
Prairie cupgrass, tumble windmillgrass, yellow
nutsedge, annual spurges, wild buckwheat,
lambsquarters, Russian thistle, velvetleaf,
morninnglory, waterhemp
Glyphosate Resistant Weeds
Glyphosate Resistant weeds?
Annual ryegrass:
1996 - Australia, California, South
America,S. Africa
Goosegrass:
1997 - Malaysia
Horseweed/marestail: 2000 - East and SE US.
probably in Kansas
Common Ragweed: 2004 - Missouri
Palmer Amaranth:
2005 - Georgia, Tennessee
Waterhemp:
2005 - Missouri
Johnsongrass:
2006 - Argentina
Giant Ragweed:
2006 - Ohio, Indiana
Lambsquarters?
Glyphosate-Resistant Waterhemp Biotype in NW MO
Kevin Bradley, University of Missouri
Continuous soybeans for many years, RR soybeans with at
least one application of glyphosate since 1996
Waterhemp also ALS and PPO resistant, but not triazine
resistant
None
Kevin Bradley,
University of Missouri
1 pt
1 qt
2 qt
1 gal
(Rate of 3# ae glyphosate/A)
2 gal
Common Waterhemp Biotype Response to 0.75 lb ae Glyphosate/A
Susceptible
Moderately Tolerant
Kevin Bradley, University of Missouri
Resistant
WeatherMax 88 oz at 1 inch
Glyphosate Resistant Palmer Amaranth
Stanley Culpepper, University of Georgia
WeatherMax 88 oz at 4 inch
WeatherMax 88 oz at 12 inch
Glyphosate Resistant Palmer Amaranth in Georgia
Sus.
WMax:
0
3
6
12
Roundup WeatherMax oz/A
Res.
Stanley Culpepper,
University of Georgia
24
48 oz/A
Glyphosate-resistant Palmer amaranth: Stanley Culpepper, Georgia, 2005.
Current Glyphosate Resistance
Evaluations at KSU
Common Waterhemp (2 populations)
Marestail (2 populations)
Giant Ragweed (2 populations)
Kochia
Glyphosate Resistant Marestail Assay
Sumner Co.
Miami Co.
Check
Glyphosate Rate: 1 pt
1 qt
1.5 qt
0
Glyphosate Resistant Marestail Assay
Sumner Co.
Miami Co.
Check
Glyphosate Rate: 1 pt
1 qt
1.5 qt
0
Glyphosate Resistant Giant Ragweed Assay
R?
S
Rate: 8X
4X 3X 2.5X 2X
1.5X 1X
1/2X 1/4X 0X
Differential Waterhemp Response to Glyphosate
Glyphosate Resistant Kochia?
Poor control of a wandering row of kochia with
glyphosate was observed in a field of Roundup
Ready cotton in Stevens county, KS in the
summer of 2007.
Kochia seed was collected from the uncontrolled
plants in the cotton field in Stevens county and
from an uncropped area in Finney county in the
fall of 2007.
Greenhouse experiments were conducted to
compare the efficacy of glyphosate at various
rates on the two kochia populations.
Materials and Methods
S and R biotypes of kochia were grown in the
greenhouse and treated when plants were 4 to 6
inches tall.
Kochia plants were treated with Roundup
Weather Max at 0.38, 0.75, 1.12, 1.5, 2.25 and 3
lb ae/a (11,22, 33, 44, 66, & 88 oz/A).
Weed control was visually evaluated 2 and 4
weeks after treatment.
Kochia biotype response to glyphosate , 2 WAT.
Herbicide
Roundup WMax + AMS
“
“
“
“
“
LSD (5%)
Rate
Biotype
ae
Product Finney Stevens
(lb/a)
(oz/a)
0.38
0.75
1.12
1.5
2.25
3
11
22
33
44
66
88
(% control)
15
88
99
100
100
100
0
34
44
60
84
96
6
Kochia biotype response to glyphosate , 2 WAT.
Herbicide
Roundup WMax + AMS
“
“
“
“
“
LSD (5%)
Rate
Biotype
ae
Product Finney Stevens
(lb/a)
(oz/a)
0.38
0.75
1.12
1.5
2.25
3
11
22
33
44
66
88
(% Mortality)
0
25
85
100
100
100
0
0
0
0
30
85
14
Kochia biotype response to glyphosate , 4 WAT.
Herbicide
Roundup WMax + AMS
“
“
“
“
“
LSD (5%)
Rate
Biotype
ae
Product Finney Stevens
(lb/a)
(oz/a)
0.38
0.75
1.12
1.5
2.25
3
11
22
33
44
66
88
(% control)
32
100
100
100
100
100
0
42
76
92
100
100
Kochia biotype response to glyphosate , 4 WAT.
Herbicide
Roundup WMax + AMS
“
“
“
“
“
LSD (5%)
Rate
Biotype
ae
Product Finney Stevens
(lb/a)
(oz/a)
0.38
0.75
1.12
1.5
2.25
3
11
22
33
44
66
88
(% Mortality)
0
100
100
100
100
100
0
0
45
75
100
100
Glyphosate Resistant Kochia?
(2 WAT)
Stevens Co.
Finney Co.
Roundup
WMax:
0.38 lb 0.75 lb 1.5 lb 2.25 lb 3 lb
Untreated
(11 oz) (22 oz) (44 oz) (66 oz) (88 oz)
Glyphosate Resistant Kochia?
(5 WAT)
Stevens Co.
Finney Co.
Roundup WMax:
Untreated
0.38 lb
(11 oz)
0.75 lb
(22 oz)
1.13 lb
(33 oz)
1.5 lb
(44 oz)
2.25 lb
(66 oz)
3 lb
(88 oz)
Summary
A biotype of kochia in southwestern Kansas has
developed a low level of resistance to glyphosate.
Exclusive use of glyphosate, especially at reduced
rates may result in increased tolerance by weeds.
Producers should use labeled rates, tank-mix and/or
rotate herbicides with different modes of action to
manage and minimize the risk of further
development of glyphosate resistant weeds.
Volunteer glyphosate-tolerant
corn in High Plains wheat /
corn / fallow
Best defense against developing
glyphosate resistant weeds:
Avoid continuous, exclusive use of
glyphosate for weed control
¾
¾
¾
¾
Crop rotation, especially with non RR crops
Rotate and/or tankmix herbicides with different
sites of action, within and across years
Include other control tactics (cultivation,
prevention, crop competition, cultural practices)
“Use the proper rate at the proper time”
Herbicide and Weed Information on Internet
KSU Weed Management:
www.oznet.ksu.edu/weedmanagement/
Pesticide labels, supplements, and MSDS sheets:
www.cdms.net/
Kansas Department of Agriculture:
www.ksda.gov/default.aspx?tabid=1
Weed Science Society of America:
www.wssa.net/
K-State Research & Extension:
www.oznet.ksu.edu/
Dallas Peterson
Extension Weed Specialist
785-532-5776
[email protected]