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Getting the Most Out of Glyphosate
Dallas PetersonDepartment of Agronomy
K-State Research & Extension
Glyphosate IssuesProduct 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 ProductsMany glyphosate products Different concentrations, formulations, and adjuvant requirementsNeed to read labels carefully and follow rate and adjuvant recommendationsKSU 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 ProductsTrade name Salt lb ai/gal lb ae/gal 0.75 lb ae/ARoundup Original IPA 4 3 1 qtRoundup Original MAX K 5.5 4.5 22 ozRoundup WEATHERMAX K 5.5 4.5 22 ozTouchdown DA 3.75 3 1 qtTouchdown Total K 5 4.2 24 ozTouchdown HiTech K 6 5 19 ozDurango IPA 5.4 4 26 ozGlyphomax XRT IPA 5.4 4 26 ozMost 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 FactorsEnvironment
TemperatureHumidityDrought Stress
Rainfree Interval Time of Day
Spray VolumeWater QualityWater ConditionersDustWheel Tracks
Roundup Application Time of DayMaterial and Methods
Roundup rate: 1 pt/A
Application Stages: P: 4-8 inch velvetleaf and Palmer amaranthLP: 6-12 inch velvetleaf and Palmer amaranth
Application time of day: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 Palmer amaranth VelvetleafTime of Day Post LP Post LP
--------------(% control)-------------
6:00 am 96 85 96 47 10:00 am 99 100 99 99 1:30 pm 100 100 99 99 5:00 pm 100 99 97 97 9:00 pm 99 88 95 47
LSD 3 9
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 dewlight influence on physiological interactionsplant leaf orientation
Late postemergence glyphosate applied with spray volumes of 5, 10, and 20 gpa, Manhattan, KS 2000.
5 gpa 10 gpa 20 gpa
0
20
40
60
80
100
5 gpa 10 gpa 20 gpa
Spray Volume
% C
ontr
ol
LSD=5
Oat control 2 WAT with a reduced rate of glyphosate as influenced by spray volume, Manhattan, KS 2001.
AMS Replacements with Glyphosate in Hard Water
5% v/v Liquid AMS(2% w/w, or 17 lb/100gal)
0.5% v/vAMS Replacement
AMS Replacements with GlyphosateMaterials & Methods
Spray Volume: 15 gpa
Water Hardness: 103 Total Hardness as CaCO3
~6 grains/gal
Application: 7/12/05, 89F, 55% RH
Velvetleaf: 6-12” 5-10 leaf
Sorghum: 16” V6
Corn: 20” V6
Sunflower: 12-16” 8-10 leaf
Weed control with glyphosate plus AMS replacement adjuvants at 4 WAT, Manhattan, KS (MS200508).
Treatment
Rate
Velvet- Leaf
Sorghum
Corn
Sun-flower
---------------(% control)-------------- Roundup WMax +: 8 oz +: None 40 60 52 73 AMS 2 % w/w 77 90 83 92 Class Act NG 2.5% v/v 72 90 82 90 Alliance 1.25% v/v 65 83 77 90 Choice 0.5% v/v 30 47 42 60 Request 0.5% v/v 37 58 50 75 Speedway 0.5% v/v 42 50 50 85 Blendmaster 1% v/v 43 57 53 80 US 500 0.25% v/v 33 50 47 70 Citron 2.2 lb/100G 37 40 40 78 N-Tank 0.5% v/v 62 68 67 90 LSD (10%) 7 9 7 7
Weed control with glyphosate plus AMS replacement adjuvants at 4 WAT, Manhattan, KS , 2006 (MS200606).
Treatment
Rate
Velvet- Leaf
Sorghum
Corn
Sun-flower
---------------(% control)-------------- Roundup WMax +: 8 oz +: None 0 0 0 3 AMS 2 % w/w 50 67 70 85 Class Act NG 2.5% v/v 30 73 68 78 Alliance 1.25% v/v 17 57 57 43 Choice WM 0.5% v/v 3 0 0 5 Request 0.5% v/v 8 0 7 7 Flame 0.5% v/v 5 2 3 10 Cayuse Plus 0.5% v/v 10 5 3 7 Loadout 0.5% v/v 3 3 3 7 Citron 2.2 lb/100G 3 3 5 3 N-Tank 0.5% v/v 30 22 37 23 LSD (10%) 10 9 10 11
Weed control with glyphosate plus AMS replacement adjuvants at 9 DAT, Tribune, KS 2006 (0613Fall).
Treatment
Rate
Sorghum
Corn
Sunflower
---------(% control)---------- Roundup WMax +: 8 oz +: None 56 74 84 AMS 2 % w/w 83 90 89 Class Act NG 2.5% v/v 80 87 90 Alliance 1.25% v/v 83 78 90 Choice WM 0.5% v/v 63 69 85 Request 0.5% v/v 60 73 85 Flame 0.5% v/v 69 84 86 Cayuse Plus 0.5% v/v 69 86 86 Loadout 0.5% v/v 68 78 86 Citron 2.2 lb/100G 69 80 86 N-Tank 0.5% v/v 83 86 87 LSD (10%) 16 11 5
Weed Control and Yield Protection
Weed PressureWeed Control StrategyTiming of Weed ControlLevel of Weed Control
Soybean yield as influenced by time of weed removal, 1998.(Peterson&Regehr)
0
5
10
15
20
25
30
35
Weed Free 22 DAP 27 DAP 31 DAP 35 DAP No Removal
Herbicide Application Timing (Days after Planting)
Soyb
ean
yiel
d (B
u/A
) Glyphosate, sequential
Glyphosate, single
Soybean Stage /Weed SizeV1/<4” V2/<12” V4/<24” V5/<30”
Critical Period of Weed ControlGrowth Stage or critical period to remove weeds from a crop before significant yield loss occurs.Highly variable and dependent on:
Weed Species PresentWeed PopulationsTime of Weed Emergence Relative to Crop EmergenceCrop Management Practices
– fertility, row spacing, population, etcEnvironmental Conditions
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. AfricaGoosegrass: 1997 - Malaysia Horseweed/marestail: 2000 - East and SE US.
probably in KansasCommon Ragweed: 2004 - MissouriPalmer Amaranth: 2005 - Georgia, TennesseeWaterhemp: 2005 - MissouriJohnsongrass: 2006 - ArgentinaGiant Ragweed: 2006 - Ohio, IndianaLambsquarters?
Continuous soybeans for many years, RR soybeans with at least one application of glyphosate since 1996Waterhemp also ALS and PPO resistant, but not triazineresistant
Glyphosate-Resistant Waterhemp Biotype in NW MOKevin Bradley, University of Missouri
Kevin Bradley, University of Missouri
Susceptible Moderately Tolerant Resistant
Common Waterhemp Biotype Response to 0.75 lb ae Glyphosate/A
WeatherMax 88 oz at 1 inch
WeatherMax 88 oz at 4 inch
WeatherMax 88 oz at 12 inch
Glyphosate Resistant Palmer Amaranth Stanley Culpepper, University of Georgia
0 3 12 24 486Roundup WeatherMax oz/A
Sus.
WMax: oz/A
Res.
Stanley Culpepper, University of Georgia
Glyphosate Resistant Palmer Amaranth in Georgia
Current Glyphosate Resistance Evaluations at KSU
Common Waterhemp (2 populations)Marestail (2 populations)Giant Ragweed (2 populations)Kochia
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 MethodsS 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.
4499331.12“
84100662.25“3
1.5
0.750.38
(lb/a)ae
Rate Biotype
(% control)
6LSD (5%)9610088“
6010044“
348822“01511Roundup WMax + AMS
(oz/a)StevensFinney ProductHerbicide
Kochia biotype response to glyphosate , 2 WAT.
085331.12“
30100662.25“3
1.5
0.750.38
(lb/a)ae
Rate Biotype
(% Mortality)
14LSD (5%)8510088“
010044“
02522“0011Roundup WMax + AMS
(oz/a)StevensFinney ProductHerbicide
Kochia biotype response to glyphosate , 4 WAT.
76100331.12“
100100662.25“3
1.5
0.750.38
(lb/a)ae
Rate Biotype
(% control)
LSD (5%)10010088“
9210044“
4210022“03211Roundup WMax + AMS
(oz/a)StevensFinney ProductHerbicide
Kochia biotype response to glyphosate , 4 WAT.
45100331.12“
100100662.25“3
1.5
0.750.38
(lb/a)ae
Rate Biotype
(% Mortality)
LSD (5%)10010088“
7510044“
010022“0011Roundup WMax + AMS
(oz/a)StevensFinney ProductHerbicide
Glyphosate Resistant Kochia?(2 WAT)
Finney Co.
0.75 lb(22 oz)
0.38 lb(11 oz) Untreated
Stevens Co.
1.5 lb(44 oz)
3 lb(88 oz)
Roundup WMax:
2.25 lb(66 oz)
Glyphosate Resistant Kochia?(5 WAT)
Finney Co.
0.75 lb(22 oz)
0.38 lb(11 oz) Untreated
Stevens Co.
1.5 lb(44 oz)
3 lb(88 oz)Roundup WMax:
2.25 lb(66 oz)
1.13 lb(33 oz)
SummaryA 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.
Best defense against developing glyphosate resistant weeds:
Avoid continuous, exclusive use of glyphosate for weed control
Crop rotation, especially with non RR cropsRotate and/or tankmix herbicides with different sites of action, within and across yearsInclude 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=1Weed Science Society of America: www.wssa.net/K-State Research & Extension: www.oznet.ksu.edu/