Cover Crops for Management of Glyphosate-Resistant Palmer Amaranth

in Cotton

Mike Marshall and Colton SandersClemson University

Palmer Amaranth (Amaranthuspalmeri)

• grows faster than other pigweeds (up to 1-2” per day!!)

• Very competitive• prolific seed producer

– Up to 450,000 seeds/plant

Untreated

Glyphosate 22 oz/A

Glyphosate 44 oz/A

EPSP Synthase Inhibitor (Roundup) Herbicide

Normal Use Rate

Untreated

Thifensulfuron 0.33 oz/A

Thifensulfuron 0.66 oz/A

ALS-Inhibitor (Harmony) Herbicide

Normal Use Rate

Current Glyphosate and ALS-Resistant Palmer Amaranth Distribution in SC

Newberry

Greenwood

Williamsburg

Georgetown

Clarendon

Bamberg

Allendale

Orangeburg

Dorchester

Barnwell

Lancaster ChesterfieldMarlboro

DillonDarlington

Hampton

Jasper

Beaufort

Edgefield

McCormick SumterRichland

Florence

Marion

Cherokee

Lee

Lexington

Charleston

Abbeville

Pickens

GreenvilleSpartanburg

York

Oconee

Union Chester

Anderson Laurens

KershawFairfield

Horry

Saluda

Calhoun

Aiken

Berkeley

Colleton

Fall Planted Cover Crops for Weed Suppression

Cover Crop for Weed Suppression

Cover Crop Rolled and Terminated Prior to Planting

Crop Emergence

Effect of Residue Cover on Weed Seed Soil Bank Reduced light

reaching soil surface Reduced temperature

fluctuations in the upper soil profile

Release of chemicals inhibit germination of small seeded weeds

Cover Crop Residue Effects on Soil Moisture on Summer Crops

Fall Planted Cover Crops for Weed Suppression

Objectives

To determine efficacy of fall plantedcover crops on glyphosate-resistantPalmer amaranth populations in cotton.

To determine impact of selectedherbicide programs in conjunction withfall cover crops on cotton growth andyield.

Materials and Methods Field experiments were conducted on

growers fields and at Edisto Research andEducation Center (EREC) located nearBlackville, SC.

Cover crop mixture (rye, oats, turnip, vetch,radish, and clover) was seeded at 70 lb/Abetween October and December 2012, 2013,and 2014 in half of the field. The rest wasleft unplanted (weedy winter cover).

Cover crops/weedy cover sections wereterminated with glyphosate and 2,4-D andValor (preplant) approximately 20 daysbefore planting.

Materials and Methods (cont) Cotton variety ‘Phytogen Widestrike 499’ was

planted at 3.8 seed/ft row mid-May of eachyear.

Preemergence (PRE) herbicides were appliedafter planting followed by POST1 (APT1) at2-3 lf cotton, POST2 (APT2) at 6-8 lf cotton,and LAYBY at 18-20 inch cotton.

Palmer amaranth populations were collectedusing of 1.0 m2 quadrat at APT1, APT2, andat LAYBY.

Palmer amaranth population data and seedcotton yield data were analyzed usingANOVA.

Herbicide Programs with Cover/No Cover

Treatment 1: (High Input RR program; Using Widestrike Cotton)

Burndown: Roundup (22 oz/A) + 2,4-D (1 qt/A) +Valor (2 oz/A) [30 preplant]PRE: Reflex (1 pt/A) + Diuron (1 pt/A) + Paraquat (2 pt/A) [~4 weeks after preplant]EPOST: Roundup (22 oz/A) + Warrant (3 pt/A) [2 weeks after PRE]MPOST: Roundup (22 oz/A) + Warrant (3 pt/A) [2 weeks after EPOST]Layby: MSMA (2.67 pt/A) + Diuron (1 pt/A) [2-3 weeks after MPOST]

Treatment 2: (Low Input LL program; Using Widestrike Cotton)

Burndown: Roundup (22 oz/A) + 2,4-D (1 qt/A) [30 preplant]PRE: Reflex (1 pt/A) + Diuron (1 pt/A) [4 weeks after preplant]EPOST: Liberty (29 oz/A) + Dual Magnum (1.3 pt/A) [2 weeks after PRE]MPOST: Liberty (29 oz/A) [2 weeks after EPOST]Layby: MSMA (2.67 pt/A) + Diuron (1 pt/A) [2-3 weeks after MPOST]

Treatment 3: (High Input LL program; Using Widestrike CottonVariety)

Burndown: Roundup (22 oz/A) + 2,4-D (1 qt/A) +Valor (2 oz/A) [30 preplant]PRE: Reflex (1 pt/A) + Diuron (1 pt/A) + Paraquat (2 pt/A) [4 weeks after preplant]EPOST: Liberty (29 oz/A) + Staple (2.5 oz/A) [2 weeks after PRE]MPOST: Liberty (29 oz/A) + Dual Magnum (1.0 pt/A) [2 weeks after EPOST]Layby: MSMA (2.67 pt/A) + Diuron (1 pt/A) [2-3 weeks after MPOST]

Effect of Cover Crops on Palmer Amaranth Populations – 2012-2103

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

1 2 3 4 5 6

POST1 POST2 LAYBY

<-- No Cover Crop -->

Palm

er A

mar

anth

pop

ulat

ions

/Acr

e

Treatment

LSD (0.05) = 2024

<--- Cover Crop --->RR LL LLRR LL LL

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

1 2 3 4 5 6

POST1 POST2 LAYBY

Treatment

<--- Cover Crop --->

<-- No Cover Crop -->

Effect of Cover Crops on Palmer Amaranth Populations – 2013-14

LSD (0.05) = 3203

RR LL LLRR LL LL

Cotton Yield – 2012-2013

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

1 2 3 4 5 6

Seed

Cot

ton

Yiel

d (lb

/A)

LSD (0.05) = 396

Treatment

Cotton Yield – 2013-2014

0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

1 2 3 4 5 6

LSD (0.05) = 452

Seed

Cot

ton

Yiel

d (lb

/A)

Treatment

Burndown:Roundup (22 oz/A) + 2,4-D (1 qt/A) +Valor (2 oz/A) [30 preplant]PRE: Reflex (1 pt/A) + Diuron (1 pt/A) + Paraquat (2 pt/A) [4 weeks after preplant]EPOST: Liberty (29 oz/A) + Staple (2.5 oz/A) [2 weeks after PRE]MPOST: Liberty (29 oz/A) + Dual Magnum (1.0 pt/A) [2 weeks after EPOST]Layby: MSMA (2.67 pt/A) + Diuron (1 pt/A) [2-3 weeks after MPOST]

EREC - Cover

Burndown:Roundup (22 oz/A) + 2,4-D (1 qt/A) +Valor (2 oz/A) [30 preplant]PRE: Reflex (1 pt/A) + Diuron (1 pt/A) + Paraquat (2 pt/A) [~4 weeks after preplant]EPOST: Roundup (22 oz/A) + Warrant (3 pt/A) [2 weeks after PRE]MPOST: Roundup (22 oz/A) + Warrant (3 pt/A) [2 weeks after EPOST]Layby: MSMA (2.67 pt/A) + Diuron (1 pt/A) [2-3 weeks after MPOST]

EREC - Cover

Glyphosate POST fb Glyphosate POST

EREC – No Cover

EREC Cotton Strip Plotsw and w/o cover cropCotton without rye cover crop.

Cotton with rye cover crop.

Summary Overall, fall seeded cover crops appeared

to reduce early season emergence ofPalmer amaranth from the soil seed bank.

Postemergence Liberty based systems withresidual herbicides provided consistentlybetter Palmer amaranth control in thesestudies.

In-season cotton crop response was notobserved with the herbicide programs inthese studies.

Summary (cont) Seed cotton yields were not affected by

the cover crop or herbicide programs. A combination of cover crop and

aggressive herbicide program reducedthe Palmer amaranth emergence.

Interseeding System – Wheat/Cotton

Interseeding System System involves

planting skip row wheat

Blocking every 5th seed tube on a grain drill (7.5 in spacing)

Plant w/narrow row unit planter ~3 wks before wheat harvest

Interseeding System Wheat is

harvested Summer crop

has a 3 wk head start over double crop practice

Straw residue left helps suppress weeds

Interseeding ResultsCotton 2014

Weed Suppression in InterseededCotton

Narrow row interseeded Soybeans

Interseeded Peanuts

Acknowledgements

NRCS – National CIG grant program NRCS – SC CIG grant program SC Cotton Board SC Cotton and Soybean Growers

Questions?