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

Reported cases of herbicide-resistant weeds in US

Why is Resistance Such a Big Deal Now?

1. ALS resistant pigweeds 2.Glyphosate-resistant horseweed 3.Glyphosate-resistant ragweed 4.Glyphosate-resistant lambsquarters* 5.Glyphosate-resistant Italian ryegrass* 1. Glyphosate-resistant Palmer amaranth (pigweed) Significant Potentially Devastating *suspected not confirmed

ALS*-resistant Amaranthus species *Imidazolinones, sulfonylureas, 19 states triazolopyrimidines, pyrimidinylthiobenzoates

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 ALS-Resistant Pigweed Survey 61 locations, 21 counties 2892 plants treated 2442 plants survived (84%)

Percent of cotton acreage planted to RR varieties USDA, AMS Publ. mp-cn833.

Adoption of Roundup Ready Technology in the US (million acres) Soybean Corn Cotton

Very Small Seeded Approximately 1 mm

Shields, E.J., J.T. Dauer, M.J. VanGessel, and G. Neuman Horseweed (Conyza canadensis) seed collected in the planetary boundary layer. Weed Sci. 54: Altitude (ft) Seeds found (#/1000 m 3 )* * Approximately 33 by 33 by 33 ft

Photo credit: Larry Steckel Must Start Clean!

Photo credit: Larry Steckel

GR Horseweed Control Roundup WM 22oz Clarity 8 oz + Roundup WM 22oz Ignite 23 oz LSD = 12 % Horseweed Control Milan May 28, ,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 Steckel

Rapid Growth Becoming Extremely Large

Average Number of Seed Produced per Plant 400,000 40,000 9, , , , , , , , , ,000 Palmer Amaranth goosegrassannual bluegrass common cocklebur 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 7%

Glyphosate-resistant Palmer Amaranth Found * * * * 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 + Valor Glyphosate + Staple (Palmer 1-2”) *Cultivation, Hooded Sprays, and/or Hand Weeding Will be Required

Prowl H pt + Reflex 1 pt PRE WeatherMax 22 oz + Dual Mag 18 DAP before Pigweed emergence WeatherMax 22 oz + Direx 1.5 pt PDIR

Prowl H 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 H pt + Reflex 1 pt PRE WeatherMax 22 oz + Staple at 3 inch WeatherMax 22 oz + Direx 1.5 pt PDIR

Staple LX fl oz/A

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 PlantingTopical (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: International Survey of Resistant Weeds * Cotton Incorporated is nearing completion of a Resistance Management Bulletin Knowledge Gives Us Hope