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

2. Pigweed Problems

3. Pigweed Problems

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

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

6. 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

7. Pigweed Response To Herbicides
“Palmer amaranth more difficult to control than smooth”
Gossett and Toler (1999), Weed Technology 13:
“Pendimethalin and trifluralin controlled Palmer amaranth, redroot pigweed, and tumble pigweed less than other herbicides”
Sweat et al. (1998), Weed Technology 12:
“Significant differences in herbicide control among pigweed species. Palmer amaranth is more difficult to control.”
Mayo et al. (1995), Weed Technology 9:

8. Pigweed Identification Sources
Identification of the Weedy Pigweeds and Waterhemps of Iowa
Pigweed Identification: A Pictorial Guide to the Common Pigweeds of the Great Plains

9. Herbicide Timing

10. Palmer Amaranth Control with Blazer Applied at Different Timings
Source: Mayo et al., 1995
Weed Technology 9:

11. 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

12. Pigweed Control with Roundup WM @ 22 ozs/A
Untreated
EPOST
(21 DAP)
LPOST
(30 DAP)
SB-01-04
June 24, 2004
56 DAP

13. What happened to soil applied herbicides in cotton?

14. Herbicides Used in GA Cotton
Source: USDA Agricultural Chemical Usage Reports

15. 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

16. 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

17. Corn Production in Georgia Acres Planted
Source: GA Crop Estimates (

18. Crop Rotations in GA Irrigated Peanuts Following Corn/Grain Sorghum or Cotton
Source: UGA Extension Agent Surveys

19. 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

20. 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