Herbicide-Resistant Weeds:A Dilemma in Dixie

Culpepper, York, Steckel, Prostko

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.

WeatherMax 22 oz, 2 d after application to 16 inch Palmer

WeatherMax 33 oz/A on 3” Palmer

0

50

100

150

200

250

300

350

1955 1970 1985 2000

Nu

mb

er

of

case

sReported cases of herbicide-resistant weeds in US

Why is Resistance Such a Big Deal Now?

Why is Resistance Such a Big Deal Now?

1. ALS resistant pigweeds2. Glyphosate-resistant horseweed3. Glyphosate-resistant ragweed4. Glyphosate-resistant lambsquarters*5. Glyphosate-resistant Italian ryegrass*

1. Glyphosate-resistant Palmer amaranth (pigweed)

Significant

Potentially Devastating

*suspected not confirmed

9794

00

ALS*-resistant Amaranthus species

*Imidazolinones, sulfonylureas, 19 states

triazolopyrimidines, pyrimidinylthiobenzoates

94

02

94 95

00

9298

99 029398

9693

93

91

99

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

Prostko 2006

2005 ALS-Resistant Pigweed Survey61 locations, 21 counties

• 2892 plants treated• 2442 plants survived (84%)

100

66

97

99

98

98

98

99

99

100

98

9883 9775

97

59

Percent of cotton acreage planted to RR varieties. 20061

1USDA, AMS. 2006. Publ. mp-cn833.

0

10

20

30

40

0

2

4

6

8

10

12

0

10

20

30

40

50

60

70

80

96 97 98 99 00 01 02 03 04 05 06

98 99 00 01 02 03 04 05 0697 98 99 00 01 02 03 04 05 06

Adoption of Roundup Ready

Technology in the US

(million acres)

Soybean

CornCotton

Very Small

Seeded

Approximately 1 mm

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. 54:1063-1067.

Altitude

(ft)

230

460

Seeds found

(#/1000 m3)*

3.3

1.7

* Approximately 33 by 33 by 33 ft

Photo credit: Larry SteckelPhoto credit: Larry Steckel

Must Start Clean!Must Start Clean!

Photo credit: Larry SteckelPhoto credit: Larry Steckel

GR Horseweed Control

0 20 40 60 80 100

Roundup WM 22oz

Clarity 8 oz + Roundup WM 22oz

Ignite 23 oz

LSD = 12

% Horseweed Control

Milan May 28, 2006

2,4-D 16 oz + Roundup WM 22oz

Burndown applied 4/3/06

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

HORSEWEED Preferred Burndown Options

1. Roundup + ½ pt Clarity, mid March

2. 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.

2004 Common Horseweed Burndown Program

Photo credit: Larry SteckelPhoto credit: Larry Steckel

Rapid Growth Becoming Extremely Large

Average Number of Seed Produced per PlantAverage Number of Seed Produced per Plant

400,000

40,000 40,000 9,0000

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

450,000

PalmerAmaranth

goosegrass annualbluegrass

commoncocklebur

Top 4 Herbicide Resistant Weeds in US peanut - 175; cotton - 250; corn - 800

Attapulgus GA, September 2004

Multiple Generations – Short Seed Dormancy

Untreated

Georgia, 2006

Glyphosate 4X rate,

applied three times

Palmer Amaranth Infesting Cotton

North Carolina, 2006

Untreated Glyphosate 4X rate,

applied three times

Palmer Amaranth Infesting Cotton

Cotton Yield vs. Palmer Competition

0

500

1000

1500

2000

2500

0 1 2 3 4 5 6 7 8 9 10

Palmer Density (num/20ft)

See

d C

ott

on

Yie

ld (

lbs/

A)

7%

Glyphosate-resistant Palmer Amaranth Found

04

05

***

*Palmer populations being studied for resistance.

Resistance trait will move through pollen

Managing Glyphosate Resistance

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 + ValorGlyphosate + Staple

(Palmer 1-2”)

*Cultivation, Hooded Sprays, and/or Hand Weeding Will be Required

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

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

Prowl + Reflex PRE

Roundup + Staple 3 inch

Direx + MSMA PD

Prowl H20 1.75 pt + Reflex 1 pt PRE

WeatherMax 22 oz + Staple at 3 inch

WeatherMax 22 oz + Direx 1.5 pt PDIR

0 1.3 5.2 10.2 20.42.6Staple LX fl oz/A

2004

2006

1X glyphosate + 1X Staple; Palmer 0.5 inches when treated

Delay the arrival or spread of resistance

Resistance Management Practices

1. Reduce herbicide reliance (as practical)

2. Diversify MOAs; Multiple MOAs

a. Multiple MOAs within a crop.

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.

DELAY glyphosate-resistant Palmer in RR cotton fields with LIGHT Palmer infestations*

Resistance Management Practices

1. Reduce herbicide reliance (as practical)

2. Diversify MOAs; Multiple MOAs

a. Multiple MOAs within a crop.

b. Crop rotation; different MOAs

Resistance Management Practices

1. Reduce herbicide reliance (as practical)

2. Diversify MOAs; Multiple MOAs

a. Multiple MOAs within a crop.

b. Crop rotation; different MOAs

3. Detect resistance early

Glyphosate-resistant Palmer amaranth: Georgia, 2005

Detect Resistance Early

More on glyphosate-resistant Palmer?

From 1:30 till 2:45 in Grand Ballroom C

- distribution, pollen dispersal, and management

How Bad Will Glyphosate-Resistant Palmer Amaranth Become?

“This Palmer amaranth stuff makes me glad I am 18 months from retirement.”

Dr. Alan York

• 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

Knowledge Gives Us Hope