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Corn Weed Management
for “New” County
Extension Agents
Eric P. Prostko
Extension Weed Specialist
Department of Crop & Soil
Sciences - UGA
April 2007
Cultural Practices
 Planting Date
 Row Spacing
 Fertility
 give the crop a
competitive edge
against weeds
Mechanical Cultivation
Time
Diesel fuel
prices
Strip-tillage
Insecticide/Herbicide Interactions
 Insecticides
Organophosphates
(OP’S)
Counter, Lorsban,
Thimet
 Herbicides
Accent, Beacon,
Option, Callisto,
Steadfast, Basis
Weed/Disease Interactions
 Maize Dwarf Mosaic
Virus (MDMV)
 Maize Chlorotic Dwarf
Virus (MCDV)
 johnsongrass
 aphid/leafhoppers
 Accent/Beacon
 hybrid tolerance
Corn Stages of Growth
Specific Herbicides
 Atrazine
 Prowl
 Accent
Atrazine Use in Field Corn
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Since 1958
foundation
inexpensive
excellent crop tolerance
PPI, PRE, POST (12”)
broad-spectrum
up to 2.5 lb ai/A/year
easily tank-mixed
weak on T. panicum
does not last full season in SE
Conventional Weed Management Systems
Many Pre-Mixes Available
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Bicep II Magnum (atrazine + Dual II Magnum)
Lariat/Bullet (atrazine + Lasso)
Lexar (atrazine + Dual Magnum + Callisto)
many others
preemergence
a good choice if many different weed species are
present
 need 0.5” of rainfall or irrigation within 7-10 days
for activation
Prowl Use in Field Corn
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since 1975
pendimethalin
DNA or “yellow”
inexpensive but….
do not apply PRE
early-post (EPOST)
 up to 30” tall or V8
 crop injury concerns
Planting depth (1.5”)
Furrow closure
Optimum Prowl/Pendimax Timing
Field Corn
Prowl will not control emerged grasses!!!
Prowl Injury In Field Corn
Prowl
Control
Accent Use in Field Corn
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since 1991
nicosulfuron
sulfonylurea
ALS-inhibitor
POST
 up to 20” tall or V6
 20-36” (PDIR)
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Pigweed, Texas panicum
Weak on crabgrass
Hybrid sensitivity
OP interaction
Tank-mix with atrazine
cost
Corn Hybrid/Herbicide Tolerance
 Pioneer
http://www.pioneer.com/CMRoot/Pioneer/usa/a
gronomy/corn/herb_table.pdf
Why do you not want to spend the money on an Accent
+ Atrazine treatment in field corn?
Accent + Atrazine
Untreated
200
Bu/A
160
168
120
113
80
40
0
Data from 18 irrigated weed control trials conducted in Georgia from 2001-2006.
At $2.00 to 3.00/bu, it only takes a 9 to 14 bu/A increase to pay for the treatment!!!
Know Your Grasses
large crabgrass
johnsongrass
Source: SWSS Weed ID Guide
fall panicum
broadleaf
signalgrass
Texas Panicum vs. Crabgrass
Fringe of
hairs
membranous
WSSA
Southern crabgrass
Texas panicum
Post-Directed Applications
Post-Directed Options for Field Corn
 Evik
 Gramoxone
Inteon/Firestorm
(paraquat)
 Lorox/Linex
 Aim
tropical spiderwort
pigweeds
morningglory
Herbicide Resistant
Corn Technologies
Should you use the RR corn system?
 advantages
Inexpensive
easy
Broad spectrum
Reduced drift concerns
No soil insecticide issues
 disadvantages
No residual
over-reliance on a single
product
Herbicide resistance
concerns
Volunteer in other RR crops
How would I use RR corn systems?
 If you are unwilling to use a PRE application of
atrazine or something else….
 2 applications of glyphosate
1st application: 21-28 DAP + atrazine (1.52.0 qt/A)
2nd application: 35-40 DAP
 Sequence (s-metolachlor + glyphosate)
 Expert (s-metolachlor + atrazine + glyphosate)
 Do not forget to include extra seed costs/A in
your budgets!
Irrigated @ 30,000/A = $12-13.00/A
Dryland @ 18,000/A = $7-8.00/A
Texas Panicum Control At Harvest with Single
or Split Applications of Roundup WM - II
Untreated
CN-04-04 (Attapulgus)
Roundup WM @ 22 ozs/A
21 DAP
Roundup WM @ 22 ozs/A
21 + 35 DAP
Corn Yield Response to Single or Split Applications
of glyphosate (4.5 lb ae/gal) @ 22 ozs/A.
210
180
181
164
150
Bu/A
120
125
90
60
30
0
Untreated
Average of 7 locations (2003-06)
DKC67-60RR
Single
Split
What about Liberty-Link Corn?
 Glufosinate
Liberty (corn)
Ignite (cotton)
 No tech fee
2007 Rebate Program
 up to 24” tall corn or V7
* Buy 20 gals and get a
$5-6/A rebate
 Tank-mix with atrazine
Liberty ATZ
 good on morningglory, Texas millet,
sicklepod
 Hybrid performance???
Garst 8353CB/LL, Hytest 7729Hx/LL
Don’t Forget Liberty-Link Corn!
83 Bu/A
Untreated
CN-10-06 (Croplan Genetics 731 HX/LL)
Ponder Farm
52 DAP
114 Bu/A
Liberty 1.67SL @ 32 ozs/A
Atrazine @ 90WG @ 1.0 lb/A
AMS @ 3 lbs/A
Applied 26 DAP
Clearfield Corn Systems
 Not used that much or
at all in Georgia
 Pursuit
 Lightning
Pursuit + Arsenal
 POST
 Non-GMO
 ALS-resistance
Common Weed Problems
Texas panicum (Texas millet, buffalograss)
sicklepod (coffeeweed)
pigweeds
morningglories
nutsedges
johnsongrass
Tropical spiderwort (Benghal dayflower)
Texas Panicum Control in Corn
What works!
 Prowl/Pendimax
(DPRE/EPOST)
 Accent (POST)
 Option (POST)
 RR or LL system
 post-directed
* Evik/Paraquat
Texas Panicum Control
OR
•About 30% of the time, Accent has provided better control of Texas panicum
•But, yields have not been different.
Texas Panicum Control (104 DAT) - II
Accent vs Option - 2004
Untreated
CN-04-04 (Attapulgus)
Applied 21 DAP
PANTE = 1-2”, 2-4 leaf
Accent @ 0.67 ozs/A
Agrioil @ 1% v/v
Option @ 1.5 ozs/A
MSO @ 1.25% v/v
AMS @ 3 lbs/A
Sicklepod Control in Corn
 Conventional Systems
Atrazine
2,4-D
Clarity
 Herbicide-Resistant
RR corn system
LL corn system
Pigweed Control in Corn
 preemergence
Atrazine
Dual/generics
Outlook
 postemergence
Atrazine
Accent
Callisto
2,4-D
Permit
Aim
glyphosate (RR corn)
 Timing is critical!
Morningglory Control in Corn
 as much atrazine as possible
 1.0 lb/A – PRE fb 1.5 lb/A –
POST
 small grain rotations
 tank-mix with Aim (POST)
 2,4-D, Clarity, Status
 Liberty-Link Corn Systems
 split applications of glyphosate
(RR corn)
 1st application + atrazine
 Harvest Aids
 2,4-D, sodium chlorate,
glyphosate, Aim, paraquat
Nutsedge Control
 not very competitive
800 plants/100 row feet
only reduce yields by 2%
 Eradicane or Sutan - PPI
 Dual II Magnum or
generic – PRE
 Glyphosate – RR corn
Split applications
 Basagran
 Permit
Johnsongrass Control in Corn
 Accent
 no OP soil insecticide
 hybrid tolerance to
Accent
 hybrid resistance to
MDMV
 Glyphosate in RR corn
Tropical spiderwort (a.k.a. Benghal dayflower)
Commelina benghalensis
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tropical Africa native
annual or perennial
seeds and rhizomes
above and below ground
flowers
 1,600 seeds/plant
 alternate host of southern
root-knot nematode
 Reservoir for southern
stem blight (white mold)
TSW in Georgia
* confirmed in 29
counties by GA Dept. of
Ag and UGA in 2004
(light blue)
* identified in 4 more
counties in 2005 (black)
*identified in 6 more
counties in 2006 (dark blue)
TSW Control in Field Corn
 Depends on planting
date
 2,4-D or Aim – POST
 Sequence or Expert in
RR corn
 Aim/Gramoxone/Evik
+ Dual Magnum –
layby
 Post-harvest may be
more important than
in-crop
Tillage
2 applications of 2,4-D,
Gramoxone, or Aim
Reduced Tillage Systems
Burndown Control Options
 glyphosate
 Paraquat
 Ignite (glufosinate)
 tank-mixes with?
 2,4-D
 atrazine
 Need a clean seedbed at planting
Ryegrass Control - Burndown
 Hard to kill with 1 shot
 Option # 1
Glyphosate @ 1.125 lb ae/A
+ atrazine @ 3 pts/A
 Option #2
Gramoxone Inteon @ 1.9
pts/A – 2 WBP fb
Gramoxone Inteon @ 1.9
pts/A + atrazine @ 3 pts/A planting
 RR corn systems
 Accent????
Herbicide-Resistant Weed Issues
 Glyphosate
 ALS
Herbicide Resistance
Definition
 inherited ability of a weed or crop biotype
to survive a herbicide application to which
the original population was susceptible.
Biotype = a group of plants within a species that has
biological traits that are not common to the population
as a whole.
Glyphosate Resistance Around the World (12
species)
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rigid ryegrass (1996)
goosegrass (1997)
horseweed (2000)
Italian ryegrass (2001)
hairy fleabane (2003)
buckhorn plantain (2003)
common ragweed (2004)
giant ragweed (2004)
Palmer amaranth (2005)
common waterhemp (2005)
johnsongrass (2005)
wild poinsettia (2005)
** Can be found in the US
**
3/15/2007
What does ALS mean?
 Acetolactate synthase
(ALS)
 Acetohydroxyacid
synthase (AHAS)
 chloroplast enzyme
needed to form certain
amino acids
Valine, leucine, isoleucine
 Herbicide families
Imidazolinones
Sulfonylureas
Sulfonanalides
benzoates
Commonly Used ALS Herbicides
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Accent
Ally/Cimarron
Beacon
Beyond
Cadre
Classic
Envoke
Exceed
Express
Finesse
FirstRate
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Glean
Harmony Extra
Maverick Pro
Osprey
Peak
Permit
Pursuit
Python
Scepter
Staple
Strongarm
ALS-Resistant Palmer Amaranth Survey
Where to go for more information?
UGA Weed Science Web-Site
www.gaweed.com
UGA Pest Control Handbook
UGA Corn Production Guide