Managing Glyphosate-Resistant Palmer Amaranth in Conventional and Strip-Till

Roundup Ready Cotton

Culpepper, Kichler, MacRae, Whitaker, York, Davis

Management Program For Glyphosate-Resistant Palmer Amaranth if Things Are Not Perfect

Strip-Till Cotton Acreage Estimates for Georgia and North Carolina

0

25

50

75

100

1997 2000 2003 2005

Strip till

% A

cres

Conservation Tillage is Very Important To the Southeast

2004 Common Horseweed Burndown Program

Photo credit: Larry SteckelPhoto credit: Larry Steckel

Hypothesis

Glyphosate-resistant Palmer amaranth will put cotton farmers out of conservation tillage production?

2006 Locations

Rocky Mount*

Macon Co.**

Materials and Methods

Split Plot Design

2 tillage practices

7 herbicide systems

Plot size

GA = 4 rows by 45 feet

NC = 4 rows by 30 feet

Herbicide Systems*

PRE POSTProwl

Roundup + Dual Mag.Prowl + CotoranProwl + StapleProwl + ReflexProwl

Roundup + StapleProwl + CotoranProwl + Reflex

*Direx + MSMA applied at layby for each herbicide program.

Herbicides and Rates

2.5 pt/AProwl H20

2 pt/ACotoran

1.7 fl ozStaple LX

1 pt/AReflex

22 oz/AWeatherMax

1 ptDual Mag.

1.7 fl ozStaple LX

PRE POST

Layby

Direx 2 pt + MSMA 2 lb

Tillage Systems

Conventional: no weeds or residue

Strip Tillage: cover controlled several weeks ahead of planting followed by Gramoxone PRE

Residues

Rocky Mount*

Macon Co.**

weeds

(little residue)

Grazed wheat

(little cover)

Thick wheat

(heavy cover)

Impact of Tillage on Locations with Little Cover*

Georgia

strip till = 67

conven = 69

North Carolina

strip till = 77

conven = 74

*Averaged over all herbicide systems.

Direx + MSMA directed over entire trial area.

Percent late-season glyphosate-resistant Palmer amaranth control. Macon Co., GA. 2006.*

0

20

40

60

80

100

GA

90 ab

+Cotoran +Reflex +Cotoran +Reflex+Staple

84 bc

WeatherMax + Dual

54 d

60

d

80 c

80 c

95 a

WeatherMax + Staple

Prowl Prowl

<25% resistant

Direx + MSMA directed over entire trial area.

Percent late-season glyphosate-resistant Palmer amaranth control. Wayne Co, NC. 2006.*

0

20

40

60

80

100

NC

91 a

+Cotoran +Reflex +Cotoran +Reflex+Staple

WeatherMax + Dual

69 b

76 b

91 a

94 a 90

a

93 a

WeatherMax + Staple

Prowl Prowl

<25% resistant

Direx + MSMA directed over entire trial area.

Seed cotton yield (lb/A). Wayne Co, NC. 2006.*

600

800

1000

1200

1400

1600

NC

1420 a

+Cotoran +Reflex +Cotoran +Reflex+Staple

WeatherMax + Dual

1160 c

1225 bc

1360 abc

1315 abc

1462 a

1536 a

WeatherMax + Staple

Prowl Prowl

Residue= 9760 lb/A

Number of plants in the non-treated control at harvest.

strip till = 8

conven = 32

# plants per sq. yard

75+% Resistant

Percent glyphosate-resistant Palmer amaranth control. Macon Co. 2006.*

Direx + MSMA directed over entire trial area.

0

20

40

60

80

100

Conv. Strip Till

0 3

30

3 13

+Cotoran +Reflex +Cotoran +Reflex+Staple

62

WeatherMax + Dual

61

WeatherMax + Staple

Prowl Prowl

75+% resistant

Glyphosate-resistant Palmer amaranth response to herbicides and tillage. Macon Co. 2006.*

0

20

40

60

80

100

Conv. Strip Till

Direx + MSMA directed over entire trial area.

0 f 3 f

30 d

73 b

3 f13 e

+Cotoran +Reflex +Cotoran +Reflex+Staple

62 c

WeatherMax + Dual

60 c

66bc 61

c

74 b

85 a

88 a

88a

WeatherMax + Staple

Prowl Prowl

Prowl + Cotoran PRE fb Roundup + Staple

Prowl + Cotoran PRE fb Roundup + Dual 4 inch fb Direx + MSMA PD

Conv Strip-Till

Prowl + Reflex PRE fb Roundup + Dual 4 inch fb Direx + MSMA PD

Conv Strip-Till

Direx + MSMA directed over entire trial area. Asterick denotes similar yield among systems.

Seed cotton yield (lb/A). Macon Co. 2006.*

0

500

1000

1500

2000

2500

3000

3500

4000

Conv. Strip Till

+Cotoran +Staple +Reflex +Cotoran+Reflex

WeatherMax + Dual

*

WeatherMax + Staple

Prowl Prowl

* * * **

Conclusions

1. Low levels of dead residue did not impact herbicidal control.

2. Heavy residue improved control.

A. Reduced pigweed emergence

B. Delayed pigweed emergence and growth

3. Heavy residue likely eliminated much of the activity of PRE herbicides placing more “pressure” on Staple POST

0 1.3 5.2 10.2 20.42.6Staple LX fl oz/A

2004

2006

0 1.3 5.2 10.2 20.42.6Staple

Wmax 0 3 12 24 486

2006

fl oz/A

fl oz/A

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