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Managing glyphosate-resistant Palmer amaranth in conventional and strip-till cotton

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Managing glyphosate-resistant Palmer amaranth in conventional and strip-till cotton. Culpepper, York, MacRae, Whitaker. Conservation Tillage is Very Important To the Southeast. Objective. Determine the impacts of conservation tillage on the management of glyphosate-resistant Palmer amaranth.

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slide1

Managing glyphosate-resistant Palmer amaranth in conventional and strip-till cotton

Culpepper, York, MacRae, Whitaker

objective
Objective
  • Determine the impacts of conservation tillage on the management of glyphosate-resistant Palmer amaranth.
slide6

Materials and Methods

Plot size

GA = 4 rows by 35-45 feet

NC = 4 rows by 25-30 feet

Split Plot/Factorial Design

7 herbicide systems

2 tillage practices

slide7

Herbicide Systems*

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

slide8

PRE

POST

Prowl H20

2.5 pt/A

Dual Mag.

1 pt

WeatherMax

22 oz/A

Cotoran

2 pt/A

Staple LX

1.7 fl oz

Staple LX

1.7 fl oz

Reflex

1 pt/A

Layby

Direx 2 pt + MSMA 2 lb

Herbicides and Rates

slide9

Percent glyphosate-resistant Palmer amaranth control at harvest. Five locations, GA & NC.*

82 a

77 ab

74 ab

70 b

64bc

56

c

40 d

Prowl

Prowl

+Reflex

+Cotoran

+Staple

+Cotoran

+Reflex

WeatherMax + Dual

WeatherMax + Staple

Direx + MSMA directed over entire trial area.

slide10

Seed Cotton Yield. Five locations, GA & NC.*

1563 a

1413 a

1416 a

1335 a

1040 b

972 bc

724 c

Prowl

Prowl

+Reflex

+Cotoran

+Staple

+Cotoran

+Reflex

WeatherMax + Dual

WeatherMax + Staple

Direx + MSMA directed over entire trial area.

slide11

Tillage Systems

Conventional: no weeds or residue

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

slide15

Percent glyphosate-resistant Palmer amaranth control at harvest. Tillage main effects.*

*

*

*

*An asterisk denotes control greater in strip-till production.

slide16

Number of Palmer amaranth (sq yd) infesting the non-treated control 21 to 28 DAP.

*

*

*

*An asterisk denotes less pigweed in strip-till production.

slide20

Seed Cotton Yield as Impacted by Tillage. Georgia and North Carolina. 2006-2007.

*

*

*

*An asterisk denotes significantly higher yields in strip-till production.

slide21

Conclusions Experiment 1

  • Heavy residue improved control.
    • A. Reduced pigweed emergence
    • B. Slowed pigweed emergence and growth
  • Heavy residue would likely benefit areas not infested with resistance by reducing selection pressure.
slide22

Conclusions Experiment 1

  • 3. Heavy residue would likely put more selection pressure on ALS chemistry (Staple) controlling those plants escaping residual herbicides.
slide23

Experiment 2: Materials and Methods

Herbicide systems (1st rainfall 17 DAP)

None or

Prowl + Reflex, RU + Staple, Direx + MSMA

Cover crop options

rye controlled 2 or 4 wk before planting

wheat controlled 2 or 4 wk before planting

no cover

slide24

Materials and Methods

Liter Produced (at planting)

wheat 4 WBP (knee high): 59,895 lb/A of liter

wheat 2 WBP (waist high): 66,429 lb/A of liter

rye 4 WBP (waist high): 68,607 lb/A of liter

rye 2 WBP (head high): 96,921 lb/A of liter

slide25

Percent reduction in Palmer emergence by cover crops without herbicides. 42 DAP.*

57 a

53 ab

40 b

38 b

*Compared to the no cover conventionally tilled system.

slide26

Percent Palmer amaranth control at harvest with herbicide programs. Macon County, GA. 2007.

87 a

81 a

79 ab

68 bc

59 c

slide27

Conventional tillage

Prowl + Reflex PRE

RU + Staple POST

Direx + MSMA layby

slide28

Knee high wheat

Prowl + Reflex PRE

RU + Staple POST

Direx + MSMA layby

slide29

Waist high wheat

Prowl + Reflex PRE

RU + Staple POST

Direx + MSMA layby

slide30

Cotton yield as impacted by cover crop residue. Macon County, GA . 2007.*

835 a

820 ab

780 ab

700 b

500 c

slide32

Conclusions Experiment 2

  • Heavy residue improved control.
    • A. Reduced pigweed emergence
    • B. Slowed pigweed emergence and growth
  • Heavy residue would likely put more selection pressure on ALS chemistry (Staple) controlling those plants escaping residual herbicides.
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