Palmer amaranth, benghal dayflower, and broadleaf signalgrass response to glufosinate applied alone or mixed

with 2,4-D, or dicamba

J.E. Chafin, A.S. Culpepper, and

L.B. Braxton

University of Georgia

Department of Crop and Soil Sciences

January 2010

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

Glyphosate 3 lb

Pyrithiobac 0.25 lb

Biotypes with multiple resistance to glyphosate and ALS herbicides are becoming more common across Georgia.

0

20

40

60

80

100

Before (2004) After (2008)

88

26

% a

cres

25 2000

45

*Average of Macon, Taylor, Sumpter, Schley, and Dooly counties

Glufos. (Ignite)

systems

Cultivation Hand weeding

0

Impact of GR Palmer amaranth in Georgia counties with severe infestations.*

Acres (%) treated with at least two

residual herbicide

Dryland Conservation Tillage

Prowl + Reflex PRE

Roundup + Dual POST

Direx + MSMA PD

Prowl + Reflex PRE

Ignite + Dual POST

Direx + MSMA PD

Glufosinate 0.42 lb on 5 in. Palmer amaranth

“The challenge is making applications of glufosinate to target plants less than 10 cm in height” (Coetzer et al. 2002).

Future Technology: 2,4-D or Dicamba Resistant Cotton

2,4-D resistant cotton

2,4-D sensitive cotton

Objective

• Determine the response of glyphosate- resistant Palmer amaranth to glufosinate, 2,4-D (Weedar), or dicamba (Clarity) applied alone and glufosinate mixed with 2,4-D or dicamba.

• Carpetweed, benghal dayflower, broadleaf signalgrass, and pitted morningglory

Hypothesis

• Tank mixtures of glufosinate + 2,4-D or dicamba will be more effective in controlling broadleaf weeds than glufosinate alone.

Trial Locations

Macon County(Glyphosate-resistant Palmer amaranth)

Chula(Palmer amaranth, carpetweed)

Sunbelt Expo(benghal dayflower, broadleaf signalgrass, pitted morningglory)

Treatments

A factorial arrangement of two “glufosinate” options

and seven “tank mix” options

Ignite Option: None or Ignite at 0.42 lbs

Tank mix option: 2,4-D, dicamba, or none

– 2,4-D (Weedar 64) .5, 0.75, 1.0 lb/ac

– Dicamba (Clarity) .25, 0.5, 1.0 lb/ac– None

Application Methods

• Backpack sprayer

• Broadcast

• Overtop

• 15 gal/Ac

• Drift Guard T-Jet 11002 VS

• Early morning application

• 7-9 inch weed

Conditions at Time of Application

• Moist/Wet

• Sunny conditions

• Air Temperature: 76-95 F

• % Relative Humidity: 56-74

Data Reported & Statistical Analysis

• Palmer amaranth control was combined over the three locations.

• Carpetweed, benghal dayflower, broadleaf signalgrass, and pitted morningglory

• Weed control at 20 d is reported; interaction means are reported.

Percent GR Palmer amaranth control at 20 d. Average 3 loc., GA, 2009.

0

20

40

60

80

100

0.5 lb 0.75 lb 1.0 lb1.0 lb 0.25 lb 0.5 lb

2,4-D dicamba

69 cd

77 bc

73 bcd

79 b

65 d

77 bc

90 a

Glufos-inate

Herbicide applied alone

Non-treated glufosinate

12 DAT

2,4-D at 0.75 lb

12 DAT 24 DAT

dicamba 0.5 lb

12 DAT 24 DAT

0

20

40

60

80

100

69 cd

77 bc

Glufos-inate

0.5 lb

73 bcd

79 b

65 d

77 bc

90 a

0.75 lb 1.0 lb1.0 lb 0.25 lb 0.5 lb

2,4-D dicamba

91 a 92 a 96 a91 a 91 a

96 a

= control when mixed with Ignite

Percent GR Palmer amaranth control at 20 d. Average 3 loc., GA, 2009.

glufosinate glufosinate + 2,4-D 0.75 lb

12 DAT

glufosinate glufosinate + dicamba 0.5 lb

12 DAT

0

20

40

60

80

100

66 b 58

b

Glufos-inate

0.5 lb

99 a

63 b 55

b57 b

60 b

0.75 lb 1.0 lb1.0 lb 0.25 lb 0.5 lb

2,4-D dicamba

Percent carpetweed control at 20 d. Chula, GA, 2009.

2,4-D 0.5 lb at 10 DAT

0

20

40

60

80

100

Glufos-inate

0.5 lb 0.75 lb 1.0 lb1.0 lb 0.25 lb 0.5 lb

2,4-D dicamba

99 a 99 a 99 a 99 a 99 a 99 a

= control when mixed with Ignite

Percent carpetweed control at 20 d. Chula, GA, 2009.

66 b 58

b

63 b 55

b57 b

60 b

99 a

Benghal dayflower infesting Roundup Ready cotton

0

20

40

60

80

100

Glufos-inate

0.5 lb 0.75 lb 1.0 lb1.0 lb 0.25 lb 0.5 lb

2,4-D dicamba

Percent benghal dayflower control at 20 d. Sunbelt Expo, GA, 2009.

91 a

98 a

98 a

68 c

84 b

93 a

68 c

0

20

40

60

80

100

Glufos-inate

0.5 lb 0.75 lb 1.0 lb1.0 lb 0.25 lb 0.5 lb

2,4-D dicamba

97 a 94 a

= control when mixed with Ignite

Percent benghal dayflower control at 20 d. Sunbelt Expo, GA, 2009.

91 a

98 a

98 a

68 c

84 b

93 a

68 c

0

20

40

60

80

100

Glufos-inate

0.5 lb 0.75 lb 1.0 lb1.0 lb 0.25 lb 0.5 lb

2,4-D dicamba

Percent broadleaf signalgrass control at 20 d. Sunbelt Expo, GA, 2009.

96 a

0 b0 b0 b0 b0 b0 b

0

20

40

60

80

100

Glufos-inate

0.5 lb 0.75 lb 1.0 lb1.0 lb 0.25 lb 0.5 lb

2,4-D dicamba

93 ab

92 ab

= control when mixed with Ignite

Percent broadleaf signalgrass control at 20 d. Sunbelt Expo, GA, 2009.

91 ab

91 ab

88 b

92 ab

96 a

Pitted morningglory controlled 97 to 99% by all treatments

Everman et al. noted greater than 90% control with glufosinate applied POST on pitted morningglory.

Conclusions-Palmer amaranth

• Glufosinate alone only provided 73% control

• 2,4-D alone provided 69-79% control

• Dicamba alone provided 69-90%

• Tank mixtures of glufosinate+2,4-D or dicamba at least 91% control

• Glufosinate alone provided 99% control

• 2,4-D alone provided 58-66%

• Dicamba alone provided 55-60%

• All rates of glufosinate+2,4-D or dicamba provided 99% control

Conclusions-Carpetweed

Conclusions- Benghal dayflower

• Glufosinate alone provided 63% control

• 2,4-D provided 91-98% control; combinations with glufosinate could not improve control

• Dicamba control ranges from 68-93% but when combined with glufosinate control ranges from 93-97%

Conclusion-Broadleaf signalgrass

• Glufosinate alone provided 96% control and no control with 2,4-D or dicamba alone

• 2,4-D mixed with glufosinate, control ranged from 88-91%; at 1 lb/ac of 2,4-D the control was 8% less than glufosinate alone

• Dicamba mixed with glufosinate provided 92-93% control

Future Research

2,4-D resistant cotton

2,4-D sensitive cotton