Ecology and Management of Glyphosate-Resistant Palmer Amaranth

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Herbicide-Resistant Weeds A Dilemma in Dixie
Culpepper, York, Steckel, Prostko
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What is Herbicide Resistance?
(official WSSA definition)
Inherited ability of a biotype of a weed
to survive and reproduce following exposure
to a dose of herbicide normally lethal to the
wild type.
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WeatherMax 22 oz, 2 d after application to 16
inch Palmer
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WeatherMax 33 oz/A on 3 Palmer
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Reported cases of herbicide-resistant weeds in US
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Why is Resistance Such a Big Deal Now?
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Why is Resistance Such a Big Deal Now?
Significant

• 1. ALS resistant pigweeds
• Glyphosate-resistant horseweed
• Glyphosate-resistant ragweed
• Glyphosate-resistant lambsquarters
• Glyphosate-resistant Italian ryegrass

Potentially Devastating
1. Glyphosate-resistant Palmer amaranth (pigweed)
suspected not confirmed
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ALS-resistant Amaranthus species
99
99
02
98
93
93
96
00
93
98
94
92
91
94
95
97
02
94
00
Imidazolinones, sulfonylureas,
19 states
triazolopyrimidines, pyrimidinylthiobenzoates
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Commonly Used ALS Herbicides

• Accent
• Ally/Cimarron
• Beacon
• Beyond
• Cadre
• Classic
• Envoke
• Exceed
• Express
• Finesse
• FirstRate

• Glean
• Harmony Extra
• Maverick Pro
• Osprey
• Peak
• Permit
• Pursuit
• Python
• Scepter
• Staple
• Strongarm

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2005 ALS-Resistant Pigweed Survey61 locations,
21 counties

• 2892 plants treated
• 2442 plants survived (84)

Prostko 2006
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Percent of cotton acreage planted to RR
varieties. 20061
97
98
59
100
99
99
98
83
100
97
75
98
98
97
99
66
98
1USDA, AMS. 2006. Publ. mp-cn833.
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Adoption of Roundup Ready Technology in the
US (million acres)
Soybean
96 97 98 99 00 01 02 03
04 05 06
Cotton
Corn
98 99 00 01 02 03
04 05 06
97 98 99 00 01 02 03
04 05 06
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Very Small Seeded
Approximately 1 mm
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Shields, E.J., J.T. Dauer, M.J. VanGessel, and G.
Neuman. 2006. Horseweed (Conyza canadensis)
seed collected in the planetary boundary layer.
Weed Sci. 541063-1067.

• Altitude
• (ft)
• 230
• 460

• Seeds found
• (/1000 m3)
• 3.3
• 1.7

Approximately 33 by 33 by 33 ft
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Must Start Clean!
Photo credit Larry Steckel
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Photo credit Larry Steckel
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GR Horseweed Control
Milan May 28, 2006
Burndown applied 4/3/06
Clarity 8 oz Roundup WM 22oz
2,4-D 16 oz Roundup WM 22oz
Ignite 23 oz
Roundup WM 22oz
Clarity 8 oz Roundup WM 22oz fb/Gramoxone
Inteon 40 oz Caparol 24oz
Clarity 8 oz Roundup WM 22oz fb/ Roundup WM
22oz Cotoran 24oz
LSD 12
0
20
40
60
80
100
Horseweed Control
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HORSEWEED

• Preferred Burndown Options
• Roundup ½ pt Clarity, mid March
• Roundup 2 pt 2,4-D, mid March
• With either of above, consider a residual
  herbicide with the burndown, such as Valor.
• If no residual, Gramoxone
• Cotoran or Direx at planting
• or Ignite Cotoran or Direx
• at planting.

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2004 Common Horseweed Burndown Program
Photo credit Larry Steckel
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Rapid Growth Becoming Extremely Large
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Average Number of Seed Produced per Plant
peanut - 175 cotton - 250 corn - 800
Top 4 Herbicide Resistant Weeds in US
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Multiple Generations Short Seed Dormancy
Attapulgus GA, September 2004
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Palmer Amaranth Infesting Cotton
Untreated
Glyphosate 4X rate, applied three times
Georgia, 2006
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Palmer Amaranth Infesting Cotton
Untreated
Glyphosate 4X rate, applied three times
North Carolina, 2006
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Cotton Yield vs. Palmer Competition
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Glyphosate-resistant Palmer Amaranth Found
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Palmer populations being studied for resistance.
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Resistance trait will move through pollen
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Georgia and North Carolina Recommendations
At Planting Topical (1-to 4 lf cotton) Layby Directed
Yellow Reflex Glyphosate Dual Magnum (no emerged Palmer) MSMA Diuron MSMA Layby Pro MSMA Suprend MSMA Valor
Yellow Reflex Glyphosate Staple (Palmer 1-2) MSMA Diuron MSMA Layby Pro MSMA Suprend MSMA Valor
Cultivation, Hooded Sprays, and/or Hand Weeding
Will be Required
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Prowl H20 1.75 pt Reflex 1 pt PRE WeatherMax
22 oz Dual Mag 18 DAP before Pigweed
emergence WeatherMax 22 oz Direx 1.5 pt PDIR
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Prowl H20 1.75 pt Reflex 1 pt PRE WeatherMax
22 oz Dual Mag 24 DAP with ½ Palmer WeatherMax
22 oz Direx 1.5 pt PDIR
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Prowl Reflex PRE Roundup Staple 3 inch Direx
MSMA PD
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Prowl H20 1.75 pt Reflex 1 pt PRE WeatherMax
22 oz Staple at 3 inch WeatherMax 22 oz Direx
1.5 pt PDIR
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2004
0
1.3
5.2
10.2
20.4
2.6
fl oz/A
Staple LX
2006
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1X glyphosate 1X Staple Palmer 0.5 inches when
treated
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Delay the arrival or spread of resistance
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• Resistance Management Practices
• Reduce herbicide reliance (as practical)
• 2. Diversify MOAs Multiple MOAs
• Multiple MOAs within a crop.

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DELAY glyphosate-resistant Palmer in RR cotton
fields with LIGHT Palmer infestations
At Planting Topical (1-to 4-lf cotton) Layby Directed
Yellow Glyphosate Dual Magnum or Staple MSMA or glyphosate Diuron, Layby Pro, Suprend, or Valor
Staple will not control ALS-resistant Palmer.
Sequence can be used as the glyphosate Dual
mixture. Yellow Prowl or Treflan type products.
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• Resistance Management Practices
• Reduce herbicide reliance (as practical)
• 2. Diversify MOAs Multiple MOAs
• Multiple MOAs within a crop.
• Crop rotation different MOAs

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• Resistance Management Practices
• Reduce herbicide reliance (as practical)
• Diversify MOAs Multiple MOAs
• Multiple MOAs within a crop.
• Crop rotation different MOAs
• Detect resistance early

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Glyphosate-resistant Palmer amaranth Georgia,
2005
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Detect Resistance Early
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How Bad Will Glyphosate-Resistant Palmer Amaranth
Become?
This Palmer amaranth stuff makes me glad I am 18
months from retirement. Dr. Alan York
More on glyphosate-resistant Palmer? From 130
till 245 in Grand Ballroom C - distribution,
pollen dispersal, and management
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Knowledge Gives Us Hope

• Weed Resistance Learning Module at National
  Cotton Council Web Site http//www.cotton.org/
• International Survey of Resistant Weeds
• http//www.weedscience.org/in.asp
• Cotton Incorporated is nearing completion of a
  Resistance Management Bulletin

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