Weed Control Programs

University of Tennessee

Larry Steckel

Glyphosate-Resistant Weeds

Conyza canadensis (horseweed)

Amaranthus palmeri (Palmer amaranth)

Ambrosia trifida (giant ragweed)

Ambrosia artemisiifolia (common ragweed)

Amaranthus tuberculatus (common

waterhemp)

Lolium multiflorum (Italian ryegrass)

Sorghum halepense (Johnsongrass)

Southern United States

Photo credit: Larry Steckel

2 GR Weeds in the Same Field

Steckel 2010

Dicamba + glyphosate 30 DBP • +/- residual product like Valor or Direx

Gramoxone Inteon + Cotoran or Caparol within 5 days of planting

Cotton must emerge weed free!

GR Weed Management - Start Clean

Horseweed and early Palmer amaranth management

GR Palmer Amaranth will be Driver Weed

New Herbicide

Warrant

Encapsulated acetachlor

Rate 48 oz/A

Soybeans post up to R3

Cotton post cotyledon to 1st flower

Very comparable to Dual Mag at

16 oz/A

Post Applied Injury

3 pt Warrant +

22 oz RPM

1.3 pt Dual Mag +

22 oz RPM

Gramoxone Inteon + Reflex 14 DBP + ½” of precipitation

• Reflex can be applied PRE on course soils

• New 24c in works: “cotton may be planted immediately after Reflex application and a ½” of rain”

and/or Gramoxone Inteon + Cotoran or Caparol PRE

Dual Magnum or Warrant applied early Post tankmixed with glyphosate on 1 lf cotton

GR Weed Management – Glyphosate

Based System

Irrigated

Same early pre plant and pre options as in irrigated

Pre plant and Pre being activated

Typical GR Palmer infestation in heavily infested fields will reduce yield 100%

1 GR Palmer/sq yard emerging with cotton reduces yield 50% (Culpepper et. al 2009)

Pray for Timely Rainfall !!!!

GR Weed Management – Glyphosate

Based System

Dry Land

Concerns

What about using yellow herbicides and tillage?

Still an option for some non-HEL

Will likely provide good overall Palmer control

However, expect some inconsistent control due to past development of DNA resistant Palmer amaranth

What about new turbo till’ s ability to incorporate a herbicide?

Probably not!

Need to use hooded and directed sprayers again

Many good application options

Direx + MSMA

Layby Pro + MSMA

Gramoxone Inteon + Direx + Valor, etc

GR Weed Management – Glyphosate

Based System

Dry Land

New hooded sprayer design

Cross between old dog house style and newer dolphin nosed…

Designed to get over Palmer amaranth

GR Weed Management – Glyphosate

Based System

Ropewick vs. WeedWiper

2009-32 oz/A Cotoran Pre/ 60 oz/A Ignite fb/16

oz/A Direx + 32 oz/A MSMA + 1 oz/A Valor $50.00/A of Weed Control!

GR Palmer Amaranth Management in Cotton

Ignite Based System

Pre Emergence 1 to 2 lf

Ignite +/-

Dual Mag

AND 5 to 7 lf AND/OR

Dual Magnum or

Warrant +/-

Glyphosate or

Ignite

Cotoran/Caparol on

any soil or

Reflex on coarse

soils

P.Direct

Direx + MSMA

On larger Palmer

or cotton

Gramoxone

Inteon + Direx +

Valor

Hooded

GR Weed Management – Ignite Based

System

Concerns

Yield loss from Ignite injury to WideStrike cotton

In GA, NC and TN 750,000 WideStrike cotton

acres were treated with at least 1 Ignite application

in 2010

Treating WideStrike cotton with two 29 oz/a Ignite

applications resulted in no yield loss (Main et al.

2010, Whitaker et al. 2010; Steckel 2007 - 2010;

Culpepper et al. 2008; etc…)

375 PHY WideStrike Tolerance to

Ignite Timing Study

Ignite application timings

Treatments consisted of 4 timings and

then all combinations of four timings

2lf, 7lf, Bloom, Bloom + 2 Weeks

Visual injury ranged from 17 to 20%

5 days after last application

Visual injury was not evident by 21

days after last application

2010 Steckel, Culpepper and York

*Combined across locations (TN and GA)

Weed free – averaged across timing

a ab b

a

Number of Ignite Applications

375 PHY WideStrike Tolerance to

Ignite Tankmix Study

Treatments: Ignite +/- (Dual Magnum,

Dimethoate, Roundup PM, and all comb.

Tankmix application timings

2lf

2009 no stress on cotton

2010 water and cold stress

2010 Steckel, Culpepper and York

375 WideStrike Cotton Tolerance to Ignite

Tankmixes

0 10 20 30 40 50

Ignite 29 oz

% Injury 5 DAA

Roundup PM 22 oz

Ignite 29 oz + Dual Mag 16 oz

Ignite 29oz + Dimethoate 4 oz

Roundup PM 22 oz + Dual Mag 16 oz

LSD = 6

Steckel, Bond and Stephenson

Ignite 29 oz + Dual Mag 16oz + Dimethoate 4 oz

Ignite 29 oz + Roundup PM 22 oz + Dual Mag 16 oz + Dimethoate 4 oz

PHY375 Tolerance Study

0 200 400 600 800 1200

Ignite 29 oz

LSD = 270

Lint Cotton Yield

Roundup PM 22 oz

Ignite 29 oz + Dual Mag 16 oz

Ignite 29oz + Roundup PM 22 oz + Dimethoate 3 oz

Ignite 29oz + Roundup PM 22 oz + Dual Mag 16 oz

2 lf Application At Jackson, TN 2009

375 WideStrike Cotton Tolerance to Ignite

Tankmixes

0 300 600 900 1200 1500

Ignite 29 oz

Lbs/A Lint Cotton

Roundup PM 22 oz

Ignite 29 oz + Dual Mag 16 oz

Ignite 29oz + Dimethoate 4 oz

Roundup PM 22 oz + Dual Mag 16 oz

LSD = 220

Steckel 2010

Ignite 29 oz + Dual Mag 16oz + Dimethoate 4 oz

Ignite 29 oz + Roundup PM 22 oz + Dual Mag 16 oz + Dimethoate 4 oz

2 lf Application At Jackson, TN 2010

Ignite Injury on WideStrike Cotton 14 DAA 29 oz/A Ignite + 16 oz/A Dual Mag

Thrips Stressed 375 WideStrike Cotton

Tolerance to Ignite Insecticide Tankmixes

0 400 800 1200 1600 2000

Ignite 29 oz

Lbs/A Lint Cotton

Sequence 2.5 pt

Sequence 2.5 pt + Bidrin 3 oz

Sequence 2.5 pt + Dimethoate 6oz

Ignite 29 oz + Dimethoate 6 oz

LSD = 120

Stewart 2010

Sequence 2.5 pt + Acephate 4 oz

Ignite 29 oz + Bidrin 3 oz

Ignite 29 oz + Acephate 4 oz

GR Weed Management – Ignite Based

System

Concerns

Not completely without risk, particularly on

stressed cotton or in some tankmixes

• Thrips stressed cotton had 12% yield loss after

29 oz/A of Ignite (Stewart et al. 2010)

• Treating WideStrike with some Ignite

tankmixes showed 15% yield loss (Bond,

Stephenson and Steckel 2010)

• Applying more than two Ignite applications on

WideStrike cotton caused 12% yield loss

(Barnett, Steckel, Culpepper and York 2010)

Spraying too large Palmer

Getting poor control

Increasing the likelihood of developing Ignite resistance !!!!

GR Weed Management – Ignite Based

System

Concerns

32 oz/A Gly 4 fb 29 oz/A Ignite on 12” Palmer

Palmer Amaranth Facts

• Most competitive of the Amaranth spp.

• Growth rate 0.21 to 0.18 cm/gdd (Horak and

Loughin 2000)

• If we assume 96/70 Mid June

growing period a 2” Palmer will

grow 2.5” per day

• So a 2” Palmer amaranth will be 7” in 48

hours and too large for Ignite herbicide to

control!

21 DAA 30 oz Ignite 12” Palmer

New Technologies on the Horizon

DHT – Tolerance to several herbicides

• Soybean/Cotton tolerance to 2,4-D, and

Ignite

• Corn tolerance to Fop herbicides and

2,4-D

• ETA 2013 corn; 2015? soybean/cotton

Dow Herbicide Trait

2,4-D Resistant Cotton

2,4-D resistant

cotton

sensitive cotton

1.5 pt of 2,4-D

12 DAT 24 DAT

Ignite Ignite + 2,4-D 0.75 lb

12 DAT

2,4-D fb 2,4-D 2,4-D + Ignite fb

2,4-D + Ignite

Palmer amaranth control just prior to layby.

Macon Co., 2010.

New Technologies on the Horizon

Dicamba Trait

Soybean – tolerance to dicamba and

glyphosate

Cotton – tolerance to dicamba,

glyphosate and Ignite

• ETA 2015?

Monsanto

Dicamba + Glyphosate Tolerant Soybeans

32 oz Dicamba PRE

Dicamba + Glyphosate Tolerant Soybeans

32 oz Dicamba Post

Ignite Ignite + dicamba 0.5 lb

12 DAT

8 to 10” Tall GR Palmer Control

0 20 40 60 80 100

Clarity 16 oz

% Control 20 DAA

Clarity 16 oz + Ignite 23 oz

Clarity 32 oz

2,4-D 16 oz

Roundup PM 44 oz

2,4-D 32 oz

LSD = 10

2010 Millington, TN

2,4-D 32 oz + Ignite 23 oz

Future of Palmer Amaranth Management

In order to be successful with the new

herbicide traits WE MUST!!!

Keep Ignite an active herbicide on Palmer

amaranth

Keep PPO herbicides active on Palmer

amaranth

York 2010

Hand Weeding

Steckel 2010

Hand Weeding

Crop Rotation for GR Palmer

GR Palmer in Cotton was Better than Soybeans

Questions?