Taproot ofPalmer Amaranth

Allen 2009

Living with Palmer amaranth in Georgia cotton

Georgia counties confirmed to be infested with glyphosate-resistant Palmer amaranth.

2004 – 1 county

2005 – 2 counties

2006 – 7 counties

2007 – 10 counties

2008 – 18 counties

What makes Palmer a super weed?

1. Herbicide resistance?

2. Growth rate?

3. Large stature?

4. Competitive ability?

5. Reducing harvest efficacy?

6. Seed production?

7. Rapid spread?

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

450,000

500,000

230 K

25028 K

309 K

Giant ragweed

450 K

Number of Seed Produced per PlantNumber of Seed Produced per Plant Glyphosate-Resistant Weeds in USGlyphosate-Resistant Weeds in US

Ragweed = Harrison et al. 2001; johnsongrass = Warwick and Black (1983); horseweed = Regehr and Bazzaz (1979); waterhemp = Nordby and Hartzler (2004); Palmer amaranth = Macrae et al (2009).

Johnson-grass

Horseweed Waterhemp Palmer amaranth

Weakness of a super weed?

1. Emergence depth!

2. Seed life longevity?

3. Light requirement for emergence.

Economic survival will depend on managing the seedbank!!!!

Progress during 2009?

1. Cover crops

2. Tillage

3. Tillage + plus cover crops

4. Herbicides

Palmer requires a significant amount of sunlight to emerge!!

Staple + Reflex + Direx PRE

Roundup WMax + Parrlay POST

Direx + MSMA Layby

No deep tillage

No cover crop

No deep tillage

Rye cover crop

Palmer amaranth response to cover crops. Macon County, GA. 2009.

Significant Residue

2009 rye emerging through 2008 rye residue

Management Program?

1. Cover crops

2. Tillage

3. Deep tillage and cover crops?

No Deep Tillage Deep Turn

No Herbicide Treatment

Number of Palmer Amaranth Plants During Early Season. Macon Co., Georgia 2008.*

Palmer amaranth seedling density

Treatments

No-Break Break

AM

AP

A d

ens

ity/m

2 to

a d

ep

th o

f 5 c

m

0

2000

4000

6000

8000

10000

12000

14000

Influence of burial depth on Palmer amaranth emergence

Depth of burial (inches)

0.5" 1" 4" 16"

Pe

rce

nt (

%)

em

erg

en

ce

0

10

20

30

40

50S-Palmer amaranthR-Palmer amaranth

Keeley et al. (1987) reported 36-44% emergence at 0-1”, 7% at 2”, and 2% at 3”.

Most Palmer amaranth emerges from top inch

Palmer amaranth seed longevity

Length of burial (months)

0 3 6 9 12 18Per

cent

(%

) of

rec

over

ed s

eed

40

50

60

70

80

90

100 SusceptibleResistant

*Data are combined over 4 burial depths: 0.5”, 1”, 4”, 16”

Staple + Reflex + Direx PRE

Roundup WMax + Parrlay POST

Direx + MSMA Layby

No deep tillage

No cover crop

Deep tillage

No cover crop

Palmer amaranth response to deep tillage. Macon County, GA. 2009.

Management Program?

1. Cover crops

2. Tillage

3. Deep tillage and cover crops?

Most Palmer amaranth emerges from top inch

Staple + Reflex + Direx PRE

Roundup WMax + Parrlay POST

Direx + MSMA Layby

No deep tillage

No cover crop

Deep tillage

Rye cover crop

Palmer amaranth response to deep tillage and cover crops. Macon County, GA. 2009.

0

20

40

60

80

100

65 b

Drill Middle

per

cen

t

47 c 46 c

Reduction in Palmer emergence as affected by deep turning/cover crop residue at 16 DAP.

Macon Co., GA 2009.

Rye cover Deep turn

+ Rye cover

96 a94 a

50 c

Deep turn

Drill MiddleDrill Middle

Non-treated: 620 plant/m2.

No herbicides applied.

0

20

40

60

80

100

81 b

No deep turn

No Cover

Deep turn

No cover

Rye 7 foot when killed, rolled, planted.

Deep turn 12 inch in previous fall.

Herbicide program: Direx + Reflex + Staple PRE; RU + Parrlay POST, Direx + MSMA at layby.

per

cen

t

63 c

80 b

98 a

GR Palmer amaranth control at harvest with Roundup-based systems. Macon Co., GA 2009.

No deep turn

Rye Cover

Deep turn

Rye Cover

0

700

1400

2100

1627 b

No deep turn

No Cover

Deep turn

No cover

Rye 7 foot when killed, rolled, planted.

Deep turn 12 inch in previous fall.

Herbicide program: Direx + Reflex + Staple PRE; RU + Parrlay POST, Direx + MSMA at layby.

1298 d1524 bc

2078 a

Seed cotton yield (lb/A) with Roundup-based systems. Macon Co., GA 2009.

No deep turn

Rye Cover

Deep turn

Rye Cover

Developing Integrated Programs

Makes growers nervous Easy to adopt

Potential Benefits

1.Labor, erosion, etc..

2.Prevents GR horseweed

3.Prevents GR ryegrass

4.Reduces Palmer 80%+

5.Moisture conservation

6. herbicides overtime

7.Higher yields??????

Management Program?

1. Tillage

2. Cover crops

3. Deep tillage and cover crops?

4. Herbicide programs

Dryland Conservation Tillage

Prowl + Reflex PRE

Roundup + Dual POST

Diuron + MSMA PD

Prowl + Reflex PRE

Ignite + Dual POST

Diuron + MSMA PD

Ignite 23 oz/A

APPLY 29 OZ OF IGNITE PRIOR TO 3 INCH PALMER

WATER VOLUME AND NOZZLE TYPE IS CRITICAL

No recommendation on handout for

RR dryland in conservation tillage?

1. Run aggressive RR program

2. Plant rye to produce tremendous cover

3. Hand weed!!!

Other Information

1. Burndown

2. Acetochlor

3. PPI herbicide applications

4. Palmer seedbank

Controlling 5 inch Glyphosate-Resistant Palmer amaranth at Burndown. Macon Co., GA 2008.*

0

20

40

60

80

100

0 c

87 b94 a

58 b

Roundup Parazone

1.33 pt

70 b

Parazone +

2,4-D (1.5 pt)

Parazone +

Clarity (8 oz)

Parazone +

Diuron (1.8 pt)

Palmer control at planting, burndown applied 17 d earlier. Macon Co., GA 2009.

0

20

40

60

80

100

90 b

Valor preplant

Direx preplant

99 a

Change in Valor Label?

1. Apply Valor and then run strip tillage:

7 day plant back

HOW EFFECTIVE ARE PREPLANT APPLICATIONS?

Change in Valor Label?

When you have greater than 30% crop residue:

2. Run strip tillage and then spray Valor:

Label says 21 day plant back

TREFLAN

PPIPRE

REFLEX

PPIPRE

Percent GR Palmer amaranth control 28 DAP. Macon Co., GA. 2009.

0

20

40

60

80

100

81 a

Prowl

51 b 46 b

86 a

Treflan

PRE APPLICATIONS

RAIN 12 d after planting

PRE PPI PRE PPI

Palmer control from acetochlor, S-metolachlor, and metolachlor. Macon Co., GA 2009.

0

20

40

60

80

100

50 c

acetochlor

(1.13 lb)

80 a

S-metolachlor

(Dual Mag, 0.95 lb)

metolachlor

(Parrlay, 1.3 lb)

77 a

No Palmer up at time of application. Layby of RU + Direx applied 19 d after POST.

Tobacco:Spartan + Yellow 2008

Soybean- Roundup 2008

A.C.York, 2009

Palmer amaranth seedbank – it is the key!

YEAR 1: 5 Palmer females escape

Produce 2,000,000 seeds in cotton (50% germ)

YEAR 2:

Weed program = 99.9% control

1,000 plants per acre left at harvest

400 female plants/A

160,000,000 seeds produced in cotton (50%)

YEAR 3:

Weed program 99.9% control

80,000 plants per acre left at harvest

32,000 female plants/A = 1.28 X 1010 seed/A

Integrating cover crop residue and moldboard plowing into glyphosate-resistant Palmer

amaranth management programs will be key!

QUESTIONS OR COMMENTS?