“Oh Where, Oh Where Has My Pigweed Control Gone”

(An Update on ALS-Resistance)(An Update on ALS-Resistance)

Eric P. ProstkoExtension Weed Specialist

Department of Crop & Soil SciencesThe University of Georgia

TiftonGCPA - 2005

Pigweed Problems in 2005

6” Pigweed Treated with 4X Rate of Cadre - Grady County (20 DAT)

Causes of Herbicide Failures

• weed size**

• moisture

• temperature

• humidity

• rate

• nozzle type

• GPA

• calibration

• bad luck

• herbicide resistance

All possible reasons for poor performance should be investigatedbefore considering the possibility of resistance!!!

ALS-Resistance Around the World

• 93 species have developed resistance world-wide

• 36 species in U.S.• Why?

– very popular• low use rates• environment friendly

– single sites of action– major MOA development in late 1980’s

early 1990’s

Herbicide Resistant WeedsBy Mode of Action

Commonly Used ALS Herbicides

• Accent• Ally• Beacon• Cadre • Classic• Envoke• Exceed• Express • Finesse

• FirstRate • Harmony Extra • Osprey• Peak• Permit/Sandea• Pursuit• Python• Scepter• Staple• Strongarm

Herbicide Resistance in Georgia

Weed Year Herbicide Location

goosegrass 1992 DNA East GA

Prickly sida 1993 IMI ?

Italian ryegrass

1995 Hoelon Peach Co. Hart Co.

Palmer amaranth

2000 2005

SU/IMI glyphosate

Burke Co. Central GA

Other Counties in Georgia with Documented ALS-Resistant Palmer Amaranth

• Tested by BASF in 2005

– Colquitt

– Cook

– Mitchell

• 166 locations were also sampled by UGA weed scientists in 2005

– ALS and glyphosate

* * *

2005 ALS-Resistant Pigweed Survey61 samples, 21 counties

If ALS-Resistance is Suspected• Prowl or Sonalan

– What about DNA-resistance?

• Cautious use of ……– Classic– Cadre– Pursuit– Strongarm

• Consider adding…..– Valor– Dual Magnum– Outlook

• Don’t be afraid of Gramoxone

• Ultra Blazer or Cobra– Tank-mix with Cadre

Do you need Gramoxone?

PE-08-05July 20, 2005 (79 DAP)Attapulgus

Untreated(1471 lbs/A)

Gramoxone Max @ 8 ozs/A+ Pledge @ 8 ozs/A + NIS

@ 0.25% v/v (15 DAP)Fb Cadre @ 1 oz/A + COC

@ 1% v/v (31 DAP)(2736 lbs/A)

Cadre @ 1 oz/A + COC @ 1% v/v (31 DAP)

(2235 lbs/A)

Postemergence Herbicide ApplicationsTimeliness is the Key!!!!

Palmer Amaranth Control with Blazer Applied at Different Timings

99

5748

0

25

50

75

100

3-5" 7-9" 11-13"

Weed Heigh t

Con

trol

(%

)

Source: Mayo et al., 1995 Weed Technology 9:141-147

Am I worried about ALS-Resistant Pigweed in Peanuts?

• The problem is real!

• It is more widespread than we would like to think.

• We have plenty of tools but ….

• We have to use them.

• Increased production costs

More Information About Herbicide Resistance

• UGA Weed Science Web-Site

* http://gaweed.com

• International Survey of Resistant Weeds

* http://www.weedscience.org/in.asp