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Perplexing Pigweed Problems in 2004

Dr. Eric P. Prostko
Extension Weed Specialist
University of Georgia
Tifton, GA

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TABLE OF CONTENTS

Perplexing Pigweed Problems in 2004 Pigweed Problems - 2004 Pigweed Problems - 2004 Why such a problem? Common Pigweed (Amaranthus) Species in GA Why Palmer Amaranth? Pigweed Response To Herbicides Pigweed Identification Sources Herbicide Timing Palmer Amaranth Control with Blazer Applied at Different Timings Pigweed Control in RR Soybeans Pigweed Control with Roundup WM @ 22 ozs/A What happened to soil applied herbicides in cotton? Herbicides Used in GA Cotton Weed Control Challenges: Strip-Tillage Cadre Rate Dilemma Corn Production in Georgia: Acres Planted Crop Rotations in GA: Irrigated Peanuts Following Corn/Grain Sorghum or Cotton Herbicide Resistant Pigweed Issues Final Thoughts

SLIDE CONTENTS

Perplexing Pigweed Problems in 2004 Eric P. Prostko Extension Weed Specialist Department of Crop & Soil Sciences University of Georgia Tifton Pigweed Problems - 2004 Pigweed Problems - 2004 Why such a problem? species timing a decline in DNA and Cotoran use in cotton reduced tillage reduced rates of Cadre in peanut crop rotations resistance issues Common Pigweed (Amaranthus) Species in GA Palmer Slender Spiny Redroot Smooth Photos: SWSS Weed ID Guide Why Palmer Amaranth? grows faster than other pigweeds more competitive than other pigweeds prolific seed producer 1,000,000 seeds/plant 9-12 WAE 2 generations/year herbicide tolerance Pigweed Response To Herbicides “Palmer amaranth more difficult to control than smooth” Gossett and Toler (1999), Weed Technology 13:165-168 “Pendimethalin and trifluralin controlled Palmer amaranth, redroot pigweed, and tumble pigweed less than other herbicides” Sweat et al. (1998), Weed Technology 12:315-321 “Significant differences in herbicide control among pigweed species. Palmer amaranth is more difficult to control.” Mayo et al. (1995), Weed Technology 9:141-147 Pigweed Identification Sources Identification of the Weedy Pigweeds and Waterhemps of Iowa http://www.weeds.iastate.edu/weed-id/waterhemp/default.htm Pigweed Identification: A Pictorial Guide to the Common Pigweeds of the Great Plains http://www.oznet.ksu.edu/library/crpsl2/s80.pdf Herbicide Timing Palmer Amaranth Control with Blazer Applied at Different Timings Source: Mayo et al., 1995 Weed Technology 9:141-147 Pigweed Control in RR Soybeans SB-01-04 August 3, 2004 105 DAP EPOST = 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 Roundup WM @ 22 ozs/A Untreated EPOST (21 DAP) LPOST (30 DAP) SB-01-04 June 24, 2004 56 DAP What happened to soil applied herbicides in cotton? Herbicides Used in GA Cotton Source: USDA Agricultural Chemical Usage Reports Weed Control Challenges Strip-Tillage yellow herbicide application method split applications higher rates impregnated Prowl H20? Before or after strip-till rig more work is needed in this area Cadre Rate Dilemma 64% of peanut acres labeled use rate is 1.44 ozs/A many growers using 1.0 ozs/A cotton rotation is critical Corn Production in Georgia Acres Planted Source: GA Crop Estimates (http://www.nass.usda.gov/ga/cropests/cornall.txt) Crop Rotations in GA Irrigated Peanuts Following Corn/Grain Sorghum or Cotton Source: UGA Extension Agent Surveys Herbicide Resistant Pigweed Issues could be more of a problem than we think DNA/IMI resistant pigweed in SC IMI/ALS resistant pigweed in Burke County, GA no confirmed pigweed resistance to glyphosate anywhere in world ? Waterhemp in IA and MO Final Thoughts resistant weed surveys weed control in reduced tillage systems timing, timing, timing use residual herbicides in problem fields full rates of Cadre on difficult species corn rotations if profitable