This document summarizes a study on managing glyphosate-resistant Palmer amaranth with residual herbicides in dryland cotton. Thirteen residual herbicides were applied preemergence at 1X and 1.5X rates and evaluated for control of Palmer amaranth after rainfall activation 17 days after treatment. Reflex, Staple, and Valor provided the highest control at 78%, 78%, and 82% respectively. For postemergence applications, Staple provided the most effective control. At layby, Valor was the most effective option for controlling Palmer amaranth. The study found these herbicides to be the most effective residual options for controlling glyphosate-resistant Palmer amaranth in

1. Managing Glyphosate Resistant Palmer Amaranth with Residual
Herbicides in Dryland Cotton
J.M. Kichler1*, and A. S. Culpepper 2
1Macon County Cooperative Extension, The University of Georgia, Oglethorpe, GA 31068
Oglethorpe,
2Department of Crop and Soil Sciences, The University of Georgia, Tifton, GA 31793
Percent Residual Palmer Control, 27 d After Activation. Rainfall Activated Preemergence
Abstract Herbicides 17 DAT.
Glyphosate-resistant Palmer amaranth was confirmed in Macon County, Georgia in 2005. Producers 100
must use residual herbicides if they are going to effectively manage this pest. Dryland producers often
question the use of residual herbicides due to erratic rainfall patterns. The objective of this experiment
was to determine the most effective residual cotton herbicides that could be applied preemergence, 80
postemergence, and at layby for control of Palmer amaranth. Traditional small plot techniques were 78 a 78 a
used and each treatment was replicated 3 times. Thirteen residual herbicides were applied at a 1X and 60
60 b
1.5X rate prior to Palmer amaranth emergence. Residual herbicides included the following: Caparol,
55 b
Cotoran, Direx, Dual Magnum, Envoke, Layby Pro, Linex, Prowl H2O, Reflex, Stalwart, Suprend, and
40 44 c
Valor. Rainfall did not activate the herbicides until 17 days after application. After receiving rainfall,
Reflex, Staple, and Valor were the most effective treatments providing 78%, 78%, and 82% control, 30 d
respectively, at 44 days after treatment. 20
Materials and Methods
In 2007, a dryland field trial was conducted in Macon County on a farm with confirmed GR-Palmer 0
Caparol Cotoran Direx Prowl Reflex Staple
amaranth. Traditional small plot techniques were followed including treatments replicated 3 times. Plot
size was 6 feet by 25 feet. All herbicides were applied preemergence and were evaluated for residual Percent Residual Palmer Control, 27 d After Activation. Rainfall Activated Postemergence
activity on Palmer amaranth. This trial implemented a conventional tillage system. A factorial treatment Herbicides 17 DAT.
arrangement was used and consisted of 13 residual herbicides applied at a 1 and 1.5X rate. Rainfall
100
activated herbicides 17 days after treatment (DAT). The results show the control of the 2nd flush of GR
Palmer amaranth per the residual herbicides. The first flush of GR Palmer amaranth was controlled by a
timely Ignite application. 80
Herbicide Treatments and 1X Rates
Caparol (2 pt) Linex (2 pt) 78 a
Cotoran (2 pt) Prowl H2O (2 pt) 60
Direx (2 pt) Reflex (1 pt) 57 b
57 b
Dual Magnum (1 pt) Stalwart (1 pt)
Envoke (0.1 oz) Staple LX (1.7 oz) 40
Layby Pro (2 pt) Suprend (1.0 lb) 35 c
Valor (1.5 oz)
All treatments were applied at 1X and 1.5X rates. 20
Conclusion
Our research showed that the most effective residual herbicide options at planting included Staple or 0
Dual Mag. Stalwart Envoke Staple
Reflex. The most effective residual topical herbicide option was Staple, and our most effective layby
option was Valor. These trials were not conducted in fields with Palmer amaranth being resistant to ALS-
herbicides such as Staple. Percent Residual Palmer Control, 27 d After Activation. Rainfall Activated Layby
Herbicides 17 DAT.
“What If It Does Not Rain For 17 Days After Application of My Residual Herbicides?”
100
80 82 a
60 70 b
55 c
40 48 c
20
Valor 1.5 oz/A PRE, 0
Direx Layby Pro Suprend Valor
No Herbicide, 25 DAT Reflex 1 pt/A PRE, 25 DAT 25 DAT
1