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Georgia:

Ten Questions and Answers About Liberty-Link Soybeans

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By Jared R. Whitaker, Extension Agronomist – Soybean and Cotton, University of Georgia, Statesboro and Eric P. Prostko, Extension Agronomist – Weed Science, University of Georgia, Tifton

January 19, 2009 - The increasing threat of herbicide-resistant weeds, particularly glyphosate- and ALS-resistant Palmer amaranth (Amaranthus palmeri), has caused soybean growers in Georgia to consider weed management strategies other than Roundup-Ready. In 2009, Liberty-Link soybeans were made commercially available to aid this effort. This publication provides growers with current information about the use of the Liberty-Link soybean system in Georgia.

Text Box: Bayer CropScience
What are Liberty-Link soybeans?

Liberty-Link soybeans are genetically modified soybeans that have resistance to topical applications of glufosinate. Glufosinate is the active ingredient in Ignite herbicide. The use of Ignite on conventional or Roundup-Ready soybeans will result in severe crop injury or plant death (Figure 1). The resistance gene for glufosinate was obtained from soil bacte­rium (Streptomyces species.)

Figure 1. Ignite injury on conventional or RR soybean variet­ies.

 

Are there Liberty-Link soybean varieties adapted for production in Georgia?

In 2009, the commercial availability of Liberty-Link soybeans was limited. It is anticipated that this will rapidly change as the desire to plant Liberty-Link soybeans in the Southeast increases. However, the agronomic performance of the available Liberty-Link soybean varieties has not yet been adequately documented in Georgia. Refer to the latest edition of the UGA Soybean Variety Performance Tests for cur­rent information about Liberty-Link soybean variet­ies. UGA variety test results can be obtained online at www.swvt.uga.edu.

Figure 2. Liberty-Link soybean varieties resistant to Ignite should be contained in seed bags identified with this logo.

In 2009, the following Liberty-Link soybean varieties were included in these tests: SS LL511N, SS LL595N, Halo 4:65, Halo 4:94, Halo 5:25, and Halo 5:65. Liberty-Link soybean varieties should be sold in seed bags that contain the appropri­ate identification label (Figure 2).

How does Ignite compare to Roundup?

Based upon the chart below, Ignite is not neces­sarily a direct substitute or replacement for Roundup.

 

Roundup

Ignite

Mode of Action

EPSP
synthase
inhibitor

Glutamine
synthetase
inhibitor

Speed of Action

slow

Intermediate-fast

Translocated in plant

yes

limited

Broadleaf Weed Control

annual morningglory (Ipomoea species)

Fa

G-E

Florida beggarweed

G-E

G

Florida pusley

F

P-F

horseweed (marestail) ALS-resistant glyphosate-resistant

G
G
P

G
G
G

Palmer amaranth ALS-resistant glyphosate-resistant

E

E
P

F-G
F-G
F-G

sicklepod

G-E

G-E

smallflower morningglory

G

G-E

tropical spiderwort (Benghal dayflower)

F

P-F

Grass/Sedge Weed Control

broadleaf signalgrass

E

G

crabgrass species

E

F-G

crowfootgrass

E

G

fall panicum

E

G

goosegrass

E

P

johnsongrass (seedling)
johnsongrass (rhizome)

E
G-E

G
P-F

nutsedge (purple) nutsedge (yellow)

F-G

F

P
P

Texas millet (panicum)

E

G

aAbbreviations: E = excellent (≥ 90% control); G = good (80- 89% control); F = fair (70-79% control); P = poor (≤ 69% control).

 

Can the Liberty-Link soybean system be used to help manage the ALS- and glyphosate­resistant Palmer amaranth (Figure 3) prob‑lems in Georgia?

Yes, but application timing will be critical! Ignite is most effective on Palmer amaranth when applied before plants reach 3 inches in height. Applications made in warm temperatures (>70N F), high humidity and bright sunlight will improve the performance of Ignite. Ignite does not provide residual weed control. Ignite is rain-fast in four hours.

Figure 3. Glyphosate-resistant Palmer amaranth in soybeans, Macon County, Georgia.

Is a residual herbicide needed with the Liberty-Link system?

YES! The Liberty-Link weed control system must be used following or in combination with a residual herbicide (Figure 4). The use of residual herbicides in the Liberty-Link system will improve the control of herbicide-resistant weeds and help de­lay the development of resistance to Ignite. Residual soybean herbicides used at planting, prior to soy­bean emergence, include: Authority MTZ*, Bound­ary*, Canopy*, Dual Magnum, Envive, Intrro, Metribuzin*, Prefix, Prowl, Pursuit, Scepter, Treflan, TriCor*, and Valor. Residual herbicides that can be tank-mixed with Ignite and applied postemergence in soybean include Dual Magnum and Reflex.

Text Box: What are the optimum spray volumes and nozzle tips for use with Ignite?

Since Ignite is a contact herbicide (non-trans­located), optimum coverage is critical for success. Avoid the use of nozzle tips and spray pressures that will produce fine (<250 microns) or coarse (>350 microns) sprays. Optimum coverage with Ignite can be obtained using a minimum spray volume of 15 GPA and flat fan nozzle tips.

Does time of application influence Ignite performance?

Yes, Ignite performance can be greatly influenced by the time of application. Ignite should not be applied near twilight or dusk. The optimum time of application for Ignite is between 9:00 a.m. and 6:00 p.m.

Figure 4. Palmer amaranth control in Georgia with the Liberty-Link soybean system (2009). Top: non-treated check; Bottom: Boundary 6.5EC @ 1.5 pt/A (PRE) followed by Ignite 280 2.34SL @ 22.0 oz/A (POST). Pictures taken 54 days after planting.

Figure 5. R1 soybean growth stage. Source: Dr. Palle Pedersen, Iowa State University.

When can Ignite safely be applied to Liberty-Link soybeans?

Ignite 280 2.34SL can be applied from soybean emergence or VE up to – but not including – the bloom stage of growth or R1 (Figure 5).

*Caution: Authority MTZ, Boundary, Canopy, and TriCor contain the active ingredient metribuzin. In the past, certain soybean varieties were sensitive to this active ingredient. Contact your local county Ex­tension agent or seed dealer before using these prod­ucts on Liberty-Link soybean varieties.

What rates of Ignite can be used on Liberty-Link soybeans?

Ignite 280 2.34SL can be applied in Liberty-Link soybeans as follows:

Use Patern

1st Application

2nd Applicationa

Season
Maximum

Option 1

22 oz/A

22 oz/A

44 oz/A

Option 2

29-36 oz/Ab

none

36 oz/A

a Sequential applications should be made 10-14 days apart. b Do not apply Ignite 280 2.34SL at rates greater than 22 oz/A past the V3-V4 stage of soybean growth.

*Refer to the latest edition of the UGA Pest Management Handbook for the most current rate recommendations.

 

Are there any rotational crop concerns related to the use of Ignite on Liberty-Link soybeans?

Ignite has limited soil activity; thus, rotation re­strictions are very favorable. Labeled rotational crop restrictions for Ignite 280 2.34SL are as follows:

Rotational Crop

Plant-Back
Interval (days)

Canola, corn, cotton, rice, soybean, sugar- beets

0

Root and tuber vegetables, leafy vegeta­bles, Brassica leafy vegetables, and small grains (barley, buckwheat, oats, rye, triti­cale, wheat)

70

All other crops

180

 

References

Culpepper, A.S., A.C. York, R.B. Batts, and K.M. Jennings. 2000. Weed management in glufosinate and glyphosate-resistant soybean (Glycine max). Weed Technology 14:77-88.

Martinson, K.B., B.R. Durgan, J.l. Gunsolus, and R.B. Sothern. 2005. Time of day of application effect on glyphosate and glufosinate efficacy. On­line. Crop Management doi:10.1094/CM-2005- 0718-02-RS.

Sellers, B.A, R.J. Smeida, and W.G. Johnson. 2003. Diurnal fluctuations and leaf angle reduce glufo­sinate efficacy. Weed Technology 17:320-306.

Senseman, S.A. 2007. Herbicide Handbook. 9th Edi­tion. Champaign, IL: Weed Science Society of America. 456 pages.

Stewart, C.L., R.E. Nurse, and P.H. Sikkema. 2009. Time of day impacts postemergence weed control in corn. Weed Technology 23:346-355.