Spring Applied Burndown Options for Control of Glyphosate-resistant

Horseweed

T.W. EubankD.H. Poston, V.K. Nandula, D.B. Reynolds, D.R.

Shaw, H.R. Robinson, J.B. Blessitt, R.T. Coleman, and T. Evans

Horseweed(Conyza canadensis)

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Horseweed Emergence vs Temp1

1Averaged 3 locations 2003-2005Eubank, 2006

Introduction

• Horseweed has been documented to be resistant to many herbicide modes of action across the U.S. including,

• Glyphosate• Paraquat• ALS Inhibitors• Triazines• Ureas

Heap, 2005

Introduction

• The widespread adoption of glyphosate-resistant crops and the advent of glyphosate-resistant horseweed (Conyza canadensis (L.) Cronq.) has created a need for research investigating alternative measures of control for this troublesome weed.

Introduction

• Determining the most efficacious chemical means for controlling horseweed is imperative in reducing possible crop yield losses due to competition.

Objectives

1. Determine the most effective chemical burndown options for emerged horseweed populations.

2. Evaluate the impact of various burndown herbicides on horseweed populations.

Chemical Control

Chemical ControlMaterials and Methods

• RCB, 4 replications• Plots: 10 x 40 ft• Tractor mounted sprayer @ 15 gal/acre• Applied April 5, 2005 and March 15, 2006• Horseweed: 4 – 6 in tall

Chemical ControlMaterials and Methods

• Burndown treatments alone/+ tank-mix – Roundup WeatherMax @ 0.77 lb ae/a– Gramoxone Inteon @ 0.75 ai/a– Ignite 280 @ 0.42 lb ai/a

• Burndown treatments alone– Roundup WeatherMax @ 1.12 lb ae/a– Gramoxone Inteon @ 0.88 ai/a– Ignite 280 @ 0.53 lb ai/a

Chemical ControlMaterials and Methods

• Tank-mixed herbicide treatments– 2,4-D @ 0.75 lb ae/a– Clarity @ 0.25 lb ai/a– Valor @ 0.064 lb ai/a– Cotoran @ 0.5 lb ai/a– Caparol @ 1 lb ai/a– Harmony XP @ 0.0234 lb ai/a– Clarity + Valor @ 0.25 + 0.064 lb ai/a– Untreated

Chemical ControlMaterials and Methods

• All data analyzed in SAS with the PROC GLM procedure

• Means separated using Fisher’s protected LSD test (p = 0.05)

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WMAX@0.77

WMAX@1.12

+ 2,4-D

+ Clarity

+ Valor

+ Cotoran

+ Caparol

+ Harmony XP

+ Clarity + Valor

Horseweed Control with WeatherMax Based Burndown1

1 Treatments shown based on 4 WAT. Horseweed 4-6 in tall. WeatherMax @ 0.77 lbs ae/a with all tank mixes. Averaged from 2005 – 2006.

LSD (0.05) = 8

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75

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Pla

nts

/m2

WMAX@0.77

WMAX@1.12

+ 2,4-D

+ Clarity

+ Valor

+ Cotoran

+ Caparol

+ Harmony XP

+ Clarity + Valor

Untreated

Horseweed Populations with WeatherMax Based Burndown1

1 Horseweed plants/m2 at 6 WAT. WeatherMax @ 0.77 lb ae/a with all tank mixes. Averaged from 2005 – 2006.

LSD (0.05) = 41

Untreated 4 WAT

WeatherMax 0.77 lb ae/a2 WAT

WeatherMax 0.77 lb ae/a 4 WAT

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l Inteon@0.75

Inteon@0.88

+ 2,4-D

+ Clarity

+ Valor

+ Cotoran

+ Caparol

+ Harmony XP

Horseweed Controlwith Inteon Based Burndown1

1 Treatments shown based on 4 WAT. Horseweed 4-6 in tall. Inteon @ 0.75 lb ai/a with all tank mixes. Averaged from 2005 – 2006.

LSD (0.05) = 8

0

25

50

75

100

125

150

Pla

nts

/m2

Inteon@0.75

Inteon@0.88

+ 2,4-D

+ Clarity

+ Valor

+ Cotoran

+ Caparol

+ Harmony XP

Untreated

Horseweed Populations with Inteon Based Burndown1

1 Horseweed plants/m2 at 6 WAT. Inteon @ 0.75 lb ai/a with all tank mixes. Averaged from 2005 – 2006.

LSD (0.05) = 39

Inteon 0.75 lb ai/a2 WAT

Inteon 0.75 lb ai/a 4 WAT

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l Ignite@0.42

Ignite@0.53

+ 2,4-D

+ Clarity

+ Valor

+ Cotoran

+ Caparol

+ Harmony XP

Horseweed Control with Ignite Based Burndown1

1 Treatments shown based on 4 WAT. Horseweed 4-6 in tall. Ignite @ 0.42 lb ai/a with all tank mixes. Averaged from 2005 – 2006.

LSD (0.05) = 5

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50

75

100

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/m2

Ignite@0.42

Ignite@0.53

+ 2,4-D

+ Clarity

+ Valor

+ Cotoran

+ Caparol

+ Harmony XP

Untreated

Horseweed Populations with Ignite Based Burndown1

1 Horseweed plants/m2 at 6 WAT. Ignite @ 0.42 lb ai/a with all tank mixes. Averaged from 2005 – 2006.

LSD (0.05) = 14

Ignite 0.42 lb ai/a2 WAT

Ignite 0.42 lb ai/a 4 WAT

Conclusions

• WeatherMax alone provided only 63 – 73% control of horseweed 4 WAT.

• The addition of 2,4-D or Clarity improved WeatherMax control to greater than 90% and reduced horseweed populations by 99% compared to the untreated check.

Conclusions

• Inteon alone treated plants quickly recovered and by 4 WAT provided only 55 – 60% control.

• The addition of 2,4-D or Clarity to Inteon significantly improved control to 83%, however, horseweed populations were reduced by only 44% and 52%, respectively, when compared to the untreated.

Conclusions

• Ignite applied alone provided better than 92% control of horseweed and all tank-mix treatments were generally better than 86%.

• Horseweed populations were reduced by greater than 88% when Ignite was tank-mixed, while Ignite alone reduced populations only 65%.

Conclusions

• New horseweed emergence, after burndown alone treatments, could be responsible for slight increase in horseweed populations as compared to burndown + tank-mix treatments.

Special Thanks

• V.K. Nandula• R.T. Coleman• J.B. Blessitt• T.H. Gibson

• T.A. Evans• H.R. Robinson• E. Graves

Questions?