Roundup Ready vs. Liberty Link
Soybeans
Daniel Stephenson, Ph.D.Daniel Stephenson, Ph.D.
Weed Scientist
LSU AgCenter
Got to understand the herbicide
first!
• Not just Roundup Ready vs. Liberty Link
• Not just Ignite vs. Roundup PowerMax or • Not just Ignite vs. Roundup PowerMax or
Touchdown Total or generic glyphosate
• GLYPHOSATE vs. GLUFOSINATE
Glyphosate vs. Glufosinate
• Both are non-selective herbicides
• Broad-spectrum annual and perennial broadleaf
and grass weed control
• Chemical structures
HO C CH CH2 CH2 P O ║ ║
O O
CH3
−NH4
+
NH2
HO C CH2 NH CH2 P O NH3 CH ║ ║
O O
OH CH3
CH3
− +Glyphosate isopropylamine salt
Glufosinate ammonium salt
Glyphosate
• Mode of action:
• Inhibits enolpyruvyl shikimate-3-phosphate (EPSP)
synthase
• EPSP inhibition depletes
• aromatic amino acids tryptophan, tyrosine, and phenylalanine
• All needed for protein synthesis or biosynthetic pathways leading
to plant growth
• Symptomology:
• Foliar chlorosis and necrosis within 4-7 days for highly
susceptible plants and within 10-20 days for less
susceptible plants.
• Chlorosis 1st in immature leaves and growing points.
Glyphosate
• Absorption and translocation:• Moderately absorbed through cuticle. WHY NIS IS NEEDED!
• Symplast translocation with accumulation in
• Underground tissues
• Immature tissues
• Meristems
• Behavior in soil
• Rapidly and tightly absorbed to soil
• No soil-activity
• Degraded microbially in soil and water
Glufosinate
• Mode of action:
• Inhibits glutamine synthetase and production of glutamine
• Glutamine synthetase inhibition
• Affects the enzyme that converts glutamate and ammonia to
glutamine
• Accumulation of ammonia destroys cells and inhibits photosystem • Accumulation of ammonia destroys cells and inhibits photosystem
I and II reactions.
• Ammonia reduces the pH gradient across the cell membrane when
can uncouple photoposphorylation.
• Symptomology:
• Chlorosis and wilting within 3-5 days. Necrosis in 7-14
days. Rate of symptoms increased by bright sunlight, high
humidity, and moist soil.
Glufosinate
• Absorption and translocation:• Requires a 6 hour rain-free period for max activity
• Xylem or phloem movement limited
• Behavior in soil
• Weakly absorbed to soil• Weakly absorbed to soil
• No soil-activity
• Degraded rapidly microbially in soil and water
Compare MOA’s
• GLYPHOSATE• Inhibits amino acid
biosynthesis
• Chlorosis and necrosis 10-20
days
• Symptoms seen in
• Immature leaves
• GLUFOSINATE• Inhibits glutamine synthetase
activity with ammonia build-
up
• Chlorosis and necrosis 3 to 14
days
• Symptoms seen in• Immature leaves
• Growing points
• Good absorption and
translocation
• Symptoms seen in
• Foliage primarily
• Poor absorption and
translocation
paraquat
No absorption/translocation
What it touches, it hurts
glyphosate
absorption/translocation needed
to kill the plant
glufosinate
Little to no A&T. Coverage crucial.
Works better with high temps and humidity
glyphosate
glufosinate
paraquat
RR vs. LL Soybean• Amounts of herbicide
• Glyphosate
• Soybean cracking to R2 = 2.25 lb ae/A
• 3 applications of 22 oz/A of Roundup PowerMax or 32 oz/A of a generic 4 lb glyphosate
• Maximum in-crop application = 1.54 lb ae/A
• 44 oz/A of Roundup PowerMax or 66 oz/A of generic 4 lb glyphosate
• Glufosinate
• Limited to # of applications
• 2, 22 oz/A applications of Ignite = total/year of 44 oz/A/year
• 1, 29-36 oz/A application = total/year of 36 oz/A/year
• Difference?
• Greater rate and # of glyphosate applications available – RESISTANCE!
• Have to utilize additional herbicides besides Ignite because of limitation in
rate and # of applications.
RR vs. LL Soybean Research
St. Joseph, LA – Northeast Res. Station
• 2 x 3 x 3 factorial arranged in a randomized complete block
design
• 4 replications
Alexandria, LA – Dean Lee REC
RR vs. LL Soybean Research
Trial Information
Roundup Ready variety Pioneer 94M80
Liberty Link variety S080120
Seeding rate 123,500 seed/Acre
Planting date April 30th
Emergence date May 4th
Row spacing 38-in single-row
Harvest date August 9th
RR vs. LL Soybean Research• Factor 1 – Soybean variety/herbicide tolerance trait:
– Roundup Ready (Roundup PowerMax @ 22 oz/A)
– Liberty Link (Ignite @ 22 oz/A)
• Factor 2 – timing of 1st application:
– 10 d after emergence DAE– 10 d after emergence DAE
– 15 DAE
– 20 DAE
• Factor 3 – timing of sequential application:
– 10 d after 1st application (DA 1st applic.)
– 15 DA 1st applic.
– 20 DA 1st applic.
barnyardgrass
At harvest – Variety x 1st applic. timing
AA A
B
C
D
goosegrass
At harvest – Variety x 1st applic. timing
A A A
B
C
D
Palmer amaranth
At harvest – Variety x 1st applic. timing
A A A
B
C
D
entireleaf morningglory
At harvest – Variety x 1st applic. timing
A A AABB
C
Soybean yield
A
B
glyphosate 10 DAE fb 20 DAE
glyphosate 10 DAE fb 25 DAE
glyphosate 10 DAE fb 30 DAE
glufosinate 10 DAE fb 20 DAE
glufosinate 10 DAE fb 25 DAE
glufosinate 10 DAE fb 30 DAE
Photo taken July 7th
glyphosate 20 DAE fb 30 DAE
glyphosate 20 DAE fb 35 DAE
glyphosate 20 DAE fb 40 DAE
glufosinate 20 DAE fb 30 DAE
glufosinate 20 DAE fb 35 DAE
glufosinate 20 DAE fb 40 DAE
Photo taken July 7th
Summary• Barnyardgrass, goosegrass, and Palmer amaranth
– Control equal for 10, 15, or 20 DAE 1st application of glyphosate
– In Liberty Link soybean, make 1st application 10 DAE
• Entireleaf morningglory
– Control equal for all 1st application timings of glyphosate– Control equal for all 1 application timings of glyphosate
– 10 = 15 DAE > 20 DAE with glufosinate
• Soybean yield
– No herbicide application timing effect
– Roundup Ready variety > Liberty Link variety
– Amount of grass = amount of soybean entering combine at harvest
• HARVEST EFFICIENCY!!!!!!
Co-application with Ignite 17 DAT
St. Joseph, LA – barnyardgrass
42 DA sequential application
ab
a
bcbc a
a aa a
cbcbc
dc
b b b
a
St. Joseph, LA – tall morningglory
42 DA sequential applicaton
ab
c
d
a
bca
bc
a
cdd
ab b
bcd
dd bcd
St. Joseph, LA – 42 DA sequential
application
• hemp sesbania and redroot pigweed
–All treatments provided >95% control.–All treatments provided >95% control.
–No differences among any factors.
St. Joseph, LA – Soybean yield
b
aa
a
b
b
Weed Mgnt. in Narrow-Row Crops
• Weed control greater when soybean seeded in 19- to 51-cm
rows compared to 76-cm rows (De Bruin and Pederson 2008; Ethridge et al. 1989;
Hock et al. 2006; Knezevic et al. 2003)
• Required weed-free period for maximum yields was 4 to 8 wk
less for cotton seeded in 53-cm rows compared to 79- and less for cotton seeded in 53-cm rows compared to 79- and
106-cm rows (Rogers et al. 1976)
Considerations & Objective
• Soybean planting pattern in Louisiana varies from 19- to 102-
cm.
• Limited to two applications of glufosinate in soybean in
Louisiana.Louisiana.
• Can reducing the soybean row spacing allow a producer to
delay their sequential application of glufosinate?
Materials and Methods
• 4 x 5 factorial arranged in a randomized complete block with 4 replications
• Factor 1: Planting pattern
• 7.5-in, 15-in, 38-in single-row, and 38 in twin-row
• Factor 2: Ignite application (22 oz/A) timing
• Nontreated• Nontreated
• 10 DAE
• 10 fb 20 DAE
• 10 fb 30 DAE
• 10 fb 40 DAE
• All treatments applied with a tractor-mounted compressed air sprayer with
flatfan nozzles calibrated to deliver 15 gpa at 37 psi.
Sequential applications
Barnyardgrass, Browntop Millet, Goosegrass
42 d after sequential application
LSD (0.05) = 6
Palmer amaranth
42 d after sequential application
LSD (0.05) = 11
What about PRE’s?
• Investigated:
– Authority MTZ
– Boundary
– Prefix
– Metribuzin 75 DF– Metribuzin 75 DF
– Valor SX
– Etc……..
• Which one should you use in RR or LL soybean?
– Strengths and weakness of PRE and POST system need to
be matched!
PRE herbicides in soybean
14-21 DAT
What about PRE’s?
• Glyphosate– Strong on grass & most broadleaves
– Weaker on mg’s, spod, sesbania
– RESISTANCE!
• PRE’s that provide
broadleaf control
and mitigate Res.
• Glufosinate
– Strong on broadleaf weeds
– Weaker on grass and pigweeds
– Limited # of applications
• PRE’s that provide
grass and broadleaf
control to extend
applic. window.
Entireleaf morningglory, Hophornbeam copperleaf,
& Sicklepod
42 d after sequential application
EMG & HBCL
LSD (0.05) = 2
Spod
LSD (0.05) = 3
Summary• In Roundup Ready soybean
– 1st application 15-20 DAE
– Sequential application 10 to 20 DA 1st application
• In Liberty Link soybean
– 1st application 10 DAE– 1 application 10 DAE
– Sequential application 10 to 15 DA 1st application
• Addition of Flexstar to Ignite will help on grasses and pigweed
• Grass and pigweed still tough in narrow-row LL soybean
• Match PRE and POST systems!
Summary• barnyardgrass, browntop millet, and goosegrass
• Little differences between planting patterns
• Sequential applications needed
• In general, control decreased with increasing sequential DAE
• Palmer amaranth
• With one application (10 DAE) wide-rows > narrow-rows
• Sequential application at 20 DAE > 30 > 40
My advice. Know what your
getting into.
THANKS & QUESTIONS?
• Thanks to the Louisiana Soybean and Feed Grain
Research and Promotion Board for funding this research.
• Daniel Stephenson
– Dean Lee - Alexandria
– Cell: (318) 308-7225
– Office: (318) 473-6590
– Email: [email protected]