Perplexing Pigweed Perplexing Pigweed ProblemsProblems in 2004 in 2004

Eric P. ProstkoEric P. Prostko

Extension Weed SpecialistExtension Weed Specialist

Department of Crop & Soil SciencesDepartment of Crop & Soil Sciences

University of GeorgiaUniversity of Georgia

TiftonTifton

Pigweed Problems - 2004Pigweed Problems - 2004

Pigweed Problems - 2004Pigweed Problems - 2004

Why such a problem?Why such a problem? speciesspecies timingtiming a decline in DNA and a decline in DNA and

Cotoran use in cottonCotoran use in cotton reduced tillagereduced tillage reduced rates of Cadre reduced rates of Cadre

in peanutin peanut crop rotationscrop rotations resistance issuesresistance issues

Common Pigweed (Common Pigweed (AmaranthusAmaranthus) Species in GA) Species in GA

Palmer Slender Spiny

RedrootSmooth

Photos: SWSSWeed ID Guide

Why Palmer Amaranth?Why Palmer Amaranth?

grows faster than grows faster than other pigweedsother pigweeds

more competitive than more competitive than other pigweedsother pigweeds

prolific seed producerprolific seed producer– 1,000,000 seeds/plant

– 9-12 WAE

– 2 generations/year

herbicide toleranceherbicide tolerance

Pigweed Response To HerbicidesPigweed Response To Herbicides ““Palmer amaranth more difficult to control than smooth”Palmer amaranth more difficult to control than smooth”

– Gossett and Toler (1999), Weed Technology 13:165-168

““Pendimethalin and trifluralin controlled Palmer amaranth, Pendimethalin and trifluralin controlled Palmer amaranth, redroot pigweed, and tumble pigweed less than other redroot pigweed, and tumble pigweed less than other herbicides”herbicides”– Sweat et al. (1998), Weed Technology 12:315-321

““Significant differences in herbicide control among pigweed Significant differences in herbicide control among pigweed species. Palmer amaranth is more difficult to control.”species. Palmer amaranth is more difficult to control.”– Mayo et al. (1995), Weed Technology 9:141-147

Pigweed Identification SourcesPigweed Identification Sources

Identification of the Weedy Pigweeds and Identification of the Weedy Pigweeds and Waterhemps of IowaWaterhemps of Iowa– http://www.weeds.iastate.edu/weed-id/waterhemp/

default.htm

Pigweed Identification: A Pictorial Guide to the Pigweed Identification: A Pictorial Guide to the Common Pigweeds of the Great PlainsCommon Pigweeds of the Great Plains– http://www.oznet.ksu.edu/library/crpsl2/s80.pdf

Herbicide TimingHerbicide Timing

Palmer Amaranth Control with Blazer Applied at Palmer Amaranth Control with Blazer Applied at Different TimingsDifferent Timings

99

5748

0

25

50

75

100

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

Weed Heigh t

Con

trol

(%

)

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

Pigweed Control in RR SoybeansPigweed Control in RR Soybeans

96 98 9891

44

66 66 65

0

20

40

60

80

100

1.25 qt/A 1.50 qt/A 1.75 qt/A Roundup WM

EPOST LPOST

SB-01-04August 3, 2004105 DAPEPOST = 2-4” AMAPA (21 DAP)LPOST = 9-10” AMAPA (30 DAP) LSD 0.05 = 13

Sequence 5.25 EW(22 ozs/A)

Pigweed Control with Pigweed Control with Roundup WM @ 22 ozs/ARoundup WM @ 22 ozs/A

Untreated EPOST(21 DAP)

LPOST(30 DAP)

SB-01-04June 24, 200456 DAP

What happened to soil applied What happened to soil applied herbicides in cotton?herbicides in cotton?

Herbicides Used in GA CottonHerbicides Used in GA Cotton

10

3327

0

20

40

60

80

100

fluometuron glyphosate pendimethalin trifluralin

Herbicide

Are

a A

ppli

ed -

%

1997 1998 1999 2000 2001 2003

Source: USDA Agricultural Chemical Usage Reports

Weed Control ChallengesWeed Control ChallengesStrip-TillageStrip-Tillage

yellow herbicide yellow herbicide application methodapplication method– split applications

– higher rates

– impregnated

– Prowl H20?

– Before or after strip-till rig

more work is needed in more work is needed in this areathis area

Cadre Rate DilemmaCadre Rate Dilemma

64% of peanut acres 64% of peanut acres labeled use rate is 1.44 labeled use rate is 1.44

ozs/Aozs/A many growers using many growers using

1.0 ozs/A1.0 ozs/A cotton rotation is cotton rotation is

criticalcritical

Corn Production in GeorgiaCorn Production in GeorgiaAcres PlantedAcres Planted

2000

1080

600330

0

500

1000

1500

2000

2500

1974 1984 1994 2004

Year

Acr

es (

X 1

000)

Source: GA Crop Estimates (http://www.nass.usda.gov/ga/cropests/cornall.txt)

Crop Rotations in GACrop Rotations in GAIrrigated Peanuts Following Corn/Grain Irrigated Peanuts Following Corn/Grain

Sorghum or CottonSorghum or Cotton

0

15

30

45

60

75

1993 1995 1997 1999 2001 2003

Year

Acr

es -

%

Corn/Grain Sorghum Cotton

Source: UGA Extension Agent Surveys

Herbicide Resistant Pigweed IssuesHerbicide Resistant Pigweed Issues could be more of a problem could be more of a problem

than we think than we think DNA/IMI resistant DNA/IMI resistant

pigweed in SCpigweed in SC IMI/ALS resistant pigweed IMI/ALS resistant pigweed

in Burke County, GAin Burke County, GA no confirmed pigweed no confirmed pigweed

resistance to glyphosate resistance to glyphosate anywhere in world ?anywhere in world ?– Waterhemp in IA and MO

Final ThoughtsFinal Thoughts

resistant weed surveysresistant weed surveys weed control in reduced tillage systemsweed control in reduced tillage systems timing, timing, timingtiming, timing, timing use residual herbicides in problem fieldsuse residual herbicides in problem fields full rates of Cadre on difficult speciesfull rates of Cadre on difficult species corn rotations if profitablecorn rotations if profitable