Perplexing Pigweed Problems in 2004 Eric P Prostko

Perplexing Pigweed Problems in 2004 Eric P. Prostko Extension Weed Specialist Department of Crop & Soil Sciences University of Georgia Tifton

Pigweed Problems - 2004

Why such a problem? 4 species 4 timing 4 a decline in DNA and Cotoran use in cotton 4 reduced tillage 4 reduced rates of Cadre in peanut 4 crop rotations 4 resistance issues

Common Pigweed (Amaranthus) Species in GA Palmer Slender Redroot Photos: SWSS Weed ID Guide Spiny Smooth

Why Palmer Amaranth? 4 grows faster than other pigweeds 4 more competitive than other pigweeds 4 prolific seed producer – 1, 000 seeds/plant – 9 -12 WAE – 2 generations/year 4 herbicide tolerance

Pigweed Response To Herbicides 4 “Palmer amaranth more difficult to control than smooth” – Gossett and Toler (1999), Weed Technology 13: 165168 4 “Pendimethalin and trifluralin controlled Palmer amaranth, redroot pigweed, and tumble pigweed less than other herbicides” – Sweat et al. (1998), Weed Technology 12: 315 -321 4“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 4 Identification of the Weedy Pigweeds and Waterhemps of Iowa – http: //www. weeds. iastate. edu/weed-id/waterhemp/default. htm 4 Pigweed Identification: A Pictorial Guide to the Common Pigweeds of the Great Plains – http: //www. oznet. ksu. edu/library/crpsl 2/s 80. 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) Sequence 5. 25 EW (22 ozs/A) LSD 0. 05 = 13

Pigweed Control with Roundup WM @ 22 ozs/A Untreated SB-01 -04 June 24, 2004 56 DAP EPOST (21 DAP) LPOST (30 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 4 yellow herbicide application method – split applications – higher rates – impregnated – Prowl H 20? – Before or after strip-till rig 4 more work is needed in this area

Cadre Rate Dilemma 4 64% of peanut acres 4 labeled use rate is 1. 44 ozs/A 4 many growers using 1. 0 ozs/A 4 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 4 could be more of a problem than we think 4 DNA/IMI resistant pigweed in SC 4 IMI/ALS resistant pigweed in Burke County, GA 4 no confirmed pigweed resistance to glyphosate anywhere in world ? – Waterhemp in IA and MO

Final Thoughts 4 resistant weed surveys 4 weed control in reduced tillage systems 4 timing, timing 4 use residual herbicides in problem fields 4 full rates of Cadre on difficult species 4 corn rotations if profitable