Management Systems for Glyphosate-Resistant Palmer Amaranth J.R. Whitaker, A.C. York, and A.S. Culpepper

Palmer Amaranth

Back: untreated Front: glyphosate-only program

Weathermax 22 oz POST-1 Weathermax 22 oz POST-2 Weathermax 22 oz POST-3

Glyphosate-resistant Palmer amaranth has been documented in several cotton-producing states North Carolina Tennessee South Carolina Arkansas Georgia

No PRE POST 1 (1-2-leaf): WM 22 oz/A+ Dual Magnum 1 pt/A POST 2 (6-leaf): WM + Staple 1.8 oz/A Lay-by: WM + Valor 1 oz/A

Experiment 1 (Materials and Methods) Conventional tillage Study site: Mt. Olive, NC in 2007 Treatments differed only in PRE application RCBD w/ 4 replications Means from weed control and yield were separated by Fisher’s Protected LSD (p=0.05)

Mt. Olive Location High PA infestation ~1/3 Pop GR-resistant Non-treated Check WM 22 oz/A Mt. Olive Location High PA infestation 150/yd2 ~1/3 Pop GR-resistant No Staple resistance WM 22 oz/A + 2.5 oz/A Staple LX

Experiment 1 (Treatments) 5 preemergence herbicides alone: Cotoran 2 pt/A Prowl H2O 2.1 pt/A Reflex 1 pt/A Reflex 1.5 pt/A Direx 1.6 pt/A Staple 1.8 oz/A No PRE

PRE Combinations Reflex 1 pt/A + Prowl H2O 2.1pt/A + Direx 1.6 pt/A + Cotoran 2 pt/A + Staple 1.8 oz/A Direx 1.6 pt/A + Prowl H2O 2.1pt/A + Reflex 1 pt/A Staple 1.8 oz/A + Direx 1.6 pt/A

Experiment 1 (Treatments) All plots received same herbicide regiment for remainder of season: Post 1 (2-leaf cotton): Sequence 2.5 pt/A (glyphosate + s-metolachlor) Post 2 (5-leaf cotton): Touchdown Total 34 oz/A Lay-by (12” cotton): Suprend 1.25 lb/A + MSMA 6.6 2.4 pt/A

Palmer amaranth control (Individual herbicides) AB BC 90 CD D 84 78 71 68 E % Control E 51 44 No PRE Cotoran Prowl Reflex 1 pt. Direx Reflex 1.5 pt. Staple 60 days after Layby

Palmer Amaranth control (Direx combinations) BC 95 BC C 85 78 70 % Control Direx Direx + Prowl Direx + Reflex Direx + Staple 60 days after Layby

Palmer amaranth control (Reflex combinations) BCD BC 95 DE E 88 84 85 76 71 % Control Reflex 1 pt. Reflex 1.5 pt. Reflex1 + Cotoran Reflex1 + Direx Reflex1 + Prowl Reflex1 + Staple 60 days after Layby 1Reflex 1 pt/A

Palmer amaranth control (Staple Combinations) 95 95 90 % Control Staple Staple + Direx Staple + Reflex 60 days after Layby

Cotton in Mt. Olive on August 2, 2007

Yield (Individual herbicides) +94% A A A A +70% +60% +60% +60% +61% B Seed Cotton Yield lb/A 670 lbs No PRE Direx Staple Prowl Cotoran Reflex 1 pt. Reflex 1.5 pt.

Yield (Direx combinations) + 33% B B B 1040 lbs + 0% Seed Cotton Yield lb/A - 12% Direx Direx + Prowl Direx + Reflex Direx + Staple

Yield (Reflex combinations) AB AB AB 1290 lbs AB R1 + 12% R1.5 + 0% R1 + 2% R1.5 - 10% 1030 lbs B R1 - 7% R1.5 - 18% R1 - 21% R1.5 - 31% Seed Cotton Yield lb/A Reflex 1 pt. Reflex 1.5 pt. Reflex1 + Cotoran Reflex1 + Direx Reflex1 + Staple Reflex1 + Prowl 1Reflex 1 pt/A

Yield (Staple Combinations) AB + 31 % B + 8 % 1060 lbs Seed Cotton Yield lb/ A Staple Staple + Reflex Staple + Direx

Experiment 2 Management systems in no-till cotton Study conducted during 2007 in Mt. Olive, NC Treatments in factorial arrangement (RCBD) with 3 replications

Factorial Arrangement of Treatments 2 Preplant options (26 days before planting): Roundup Weathermax (WM) 22 oz/A + 2,4-D 0.5 pt/A WM + 2,4-D 0.5 pt/A + Valor SX 2 oz/A 2 PRE options: WM WM + Reflex 1 pt/A 3 Early POST options (2-leaf cotton): WM + Dual Magnum 1 pt/A WM + Staple LX 2.5 oz/A

Materials and Methods All plots received: WM 22 oz/A (6-leaf cotton) Lay-by application of Direx 2 pt/A + MSMA 6.6 2 pt/A (12” cotton) Weed control data arcsine square root transformed and subjected to ANOVA with partitioning appropriate for factorial treatment design (p=0.05) Means for main effects and interactions were separated with Fisher’s Protected LSD (p=0.05)

Palmer amaranth control 14 Days After Planting (Pre-plant Palmer amaranth control 14 Days After Planting (Pre-plant*PRE interaction) A B C 97 93 81 % Control D WM WM + Reflex WM WM + Reflex PRE: Preplant: WM + 2,4-D WM + 2,4-D + Valor

Palmer amaranth control (30 Days After Lay-by) 96 93 % Control WM + 2,4-D WM + 2,4-D + Valor Pre-plant Main Effect

Control 30 Days After Layby (PRE*Early POST) 99 99 96 95 92 85 % Control WM WM WM + Dual WM + Staple WM + Dual WM + Staple Early POST PRE WM WM + Reflex

Yield (Pre-plant main effect) B + 15 % 1530 lbs Seed Cotton Yield (lb/A) WM + 2,4-D + Valor WM + 2,4-D

Palmer amaranth control (30 Days After Lay-by) 96 93 % Control WM + 2,4-D WM + 2,4-D + Valor Pre-plant Main Effect

Palmer amaranth control 14 Days After Planting (Pre-plant Palmer amaranth control 14 Days After Planting (Pre-plant*PRE interaction) A B C 97 93 81 % Control D WM WM + Reflex WM WM + Reflex PRE: Preplant: WM + 2,4-D WM + 2,4-D + Valor

Yield (Pre-plant main effect) B + 15 % 1530 lbs Seed Cotton Yield (lb/A) WM + 2,4-D + Valor WM + 2,4-D

Yield (Preemergence Main Effect ) B + 9 % 1580 lbs Seed Cotton Yield (lb/A) WM WM + Reflex

Yield (Early POST Main Effect ) AB B + 16 % + 7 % 1530 lbs Seed Cotton Yield (lb/A) WM WM + Dual WM + Staple

Conclusions (1st Experiment) Any PRE better than nothing Most effective individual PREs were Direx, Staple, and Reflex Combinations of Staple + Direx or Staple + Reflex are best PRE options

Conclusions (2nd Experiment) Applied alone, Reflex more effective that Valor, both are best Staple POST somewhat better than Dual Magnum (if no ALS resistance) The most effective system was: Valor preplant, fb Reflex PRE, fb WM + Staple POST, and residual Lay-by

Other Systems Preplant PRE POST Lay-by Valor Direx WM + Staple LX Residual Lay-by None Reflex 1.5 pt/A WM + Dual Magnum Reflex 1 pt/A + Direx Reflex 1 pt/A + Staple Staple + Direx