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Corn Insect Management. Scott Stewart WTREC, Jackson, TN University of Tennessee Extension. The Primary I ssues. Seed treatments, at-planting insecticides A complex of soil insect pests Managing non- Bt corn Primarily for corn borers Bt corn technologies

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Corn insect management

Corn Insect Management

Scott Stewart

WTREC, Jackson, TN

University of Tennessee Extension

The primary i ssues
The Primary Issues

Seed treatments, at-planting insecticides

  • A complex of soil insect pests

    Managing non-Btcorn

  • Primarily for corn borers

    Btcorn technologies

  • There are just so many options

Corn insect management

Relative Efficacy of Corn IST

P = poor F = fair G = good E = excellent NL = not labeled

Corn at planting insecticides trial 1 2013 tennessee
Corn At-planting Insecticides, Trial 12013, Tennessee

Corn at planting insecticides trial 2 2013 tennessee
Corn At-planting Insecticides, Trial 22013, Tennessee

Capture lfr in furrow trial starkville ms 2012 catchot
Capture LFR In-furrow TrialStarkville, MS 2012 (Catchot)

All with Poncho 250






Managing soil insects
Managing Soil Insects

  • Be proactive in high risk fields

    • New fields

    • Problem fields

  • Cruiser or Poncho 250 not always enough

    • 500 rates or higher

    • In-furrow bifenthrin (Capture LFR, Brigade, etc.)

      • Will also provide protection from cutworms

    • In-furrow granular insecticides*

* Be careful of insecticide/herbicide interactions

Corn borers
Corn Borers

  • The primary target of Bt corn

    • Southwestern corn borer

    • European corn borer

  • The second generations are typically the most destructive

    • Because it is larger and affects more acres



Impact of infestation timing on yield swcb infested non bt plants steckel and stewart
Impact of Infestation Timing on YieldSWCB infested, non-Btplants (Steckel and Stewart)

P < 0.0001



P < 0.0001





Weight (g) per Ear





Infestation Timing

Scouting non bt corn
Scouting Non-Bt Corn populations (Henry Co., TN)

  • Whorl stage

    • Pretty easy

    • Look for windowpane-like lesions on emerging leaves

      • Remove whorls and unfurl leaves to look for small larvae that are present

  • Tasseling and later

    • Much more difficult and requires training

Swcb moth trapping
SWCB Moth Trapping populations (Henry Co., TN)

  • Triggers scouting or spray

Swcb pheromone trapping moths trap week henry co tn 2012
SWCB Pheromone Trapping populations (Henry Co., TN)Moths/Trap/Week (Henry Co, TN, 2012)


Scout / Spray



New southwestern corn borer threshold non bt corn
New Southwestern Corn Borer Threshold populations (Henry Co., TN)(Non-Bt Corn)

  • Treat prior to tasseling when 5 percent or more of plants are found with egg masses or live larvae

    • or 7-10 days after pheromone traps catch an average of 50 or more moths on a 7 day catch

  • Beginning at tasseling (VT) and through the milk stage (R3), treat when 10 percent or more of plants are found with egg masses or live larvae

    • or 7-10 days after pheromone traps catch an average of 100 or more moths on a 7 day catch

Insecticide selection refer to local extension recommendations
Insecticide Selection populations (Henry Co., TN)Refer to Local Extension Recommendations

First Generation (whorl)

  • Many labeled pyrethroid insecticides

    • Baythroid XL

    • Brigade (bifenthrin)

    • Karate or Warrior II

    • Mustang Max

    • Etc.

  • Others as in tassel stage

Second Generation (tassel)

  • Intrepid

  • Belt SC

  • Besiege

  • Prevathon

  • Tracer

  • Pyrethroids as in whorl stage

Direct spray into whorls as much as possible

Typically requires aerial application

The many bt corn technologies
The Many populations (Henry Co., TN)BtCorn Technologies

  • Bt corn is the primary means used to control corn borers

  • Many available Bt trait packages (old and new)

  • May or may not include Bt traits for western or northern corn rootworm

Corn insect management

Relative Efficacy of Selected Bt Corn Traits populations (Henry Co., TN)

(see handout for more inclusive list & refuge requirements)

Non bt corn refuge requirements
Non-Bt Corn Refuge Requirements populations (Henry Co., TN)

  • Cotton Counties

    • 50% for the old technologies

    • 20% for the new

      • VT2P, VT3P, SmartStax, Viptera, Optimum Intrasect, Optimum AcreMax

  • Corn Counties

    • 20% for the old technologies

    • 20, 10 or 5 % for the new

      • Refuge in bag (RIB) system for some

Cotton Counties

MISSOURI:DunklinNew MadridPemiscotScottStoddard

Products with Bt rootworm traits require an “in-field” refuge

Do these refuge requirements make sense for non cotton growing areas
Do these refuge requirements make sense populations (Henry Co., TN)?For non-cotton growing areas !!!

5% Refuge of Non-BtCorn

  • 2+ caterpillar traits, 0 rootworm traits

    • VT2P, VT2P RIB, Optimum Intrasect, Optimum AcreMax (RIB), and others

  • 2+ caterpillar traits, 2+ rootworm traits

    • SmartStax or SmartStax RIB, Optimum Acre XTreme (RIB), and others

Confirmed resistance to bt traits
Confirmed Resistance to Bt Traits populations (Henry Co., TN)

Far and Minor Pest

  • Fall armyworm to Cry 1F

    • Herculex or Herculex Xtra

    • Component of SmartStax, Optimum Intrasect and Optimum AcreMax products

  • Western corn rootworm to Cry3 Bb1

    • VT3 and VT3P

    • Component of SmartStax

    • Rotate fields to non-corn crops, rotate Bt rootworm traits, use at-planting insecticide and don’t use Bt rootworm traits if they are not needed

Close and Major Pest

Corn insect management

SWCB and ECB Injury populations (Henry Co., TN)CM Tunneling per 20 Stalks (TN, 2010)


P < 0.0001 (LSD = 89.2)


All the Bt lep traits provide near perfect control of SWCB and ECB





Bt corn in the presence of corn borers yield milan tn 2011
Bt corn in the presence of corn borers populations (Henry Co., TN)Yield (Milan, TN, 2011)


a b

Corn insect management

Leaf populations (Henry Co., TN)Injury Score for FAW Catchot, 2010, Starkville, MS

Leaf Injury Score (9-1 scale, 9 = no damage)








Optimum Intrasect


Corn insect management

Corn Earworm populations (Henry Co., TN)

The most common ear feeding caterpillar

Smartstax test 2009
SmartStax Test - 2009 populations (Henry Co., TN)





Smartstax test 2010
SmartStax Test - 2010 populations (Henry Co., TN)


VT3P or SS


Corn insect management
Approximate Reduction in Kernel Damage Compared with Non- populations (Henry Co., TN)Bt Corn(Summarized Across Multiple University Trials, Corn Earworm)

Corn insect management

Reality Check populations (Henry Co., TN)

Viptera ... “outperforms triple stacks by 14.3 bu/A under significant corn earworm pressure and up to 32 bu/A under heavy pressure”

Yield of top ten hybrids bu acre 2012 tennessee research education center tests allen et al
Yield of Top Ten Hybrids (Bu/Acre) populations (Henry Co., TN)2012 Tennessee Research & Education Center Tests (Allen, et al.)

Insecticide trial on non bt corn corn earworm injury and yield tn 2011
Insecticide Trial on Non- populations (Henry Co., TN)Bt CornCorn Earworm Injury and Yield (TN, 2011)

Application at early silking (moderate pressure)

P(yield) = 0.9148

P(kernels) = 0.0013

Insecticide yield effects on non bt corn tennessee stewart 2012
Insecticide Yield Effects on Non- populations (Henry Co., TN)Bt Corn(Tennessee, Stewart, 2012)

A lot of CEW but no treatment effects on kernel injury (P = 0.7341)

Simulated corn earworm injury milk stage steckel and stewart 2011
Simulated Corn Earworm Injury, Milk Stage populations (Henry Co., TN)Steckel and Stewart, 2011

Spraying corn for corn earworm
Spraying Corn for Corn Earworm populations (Henry Co., TN)

Foliar applications for ear stage infestations of corn earworm in field corn arenot economically practical

  • No consistent yield response except in presence of southwestern corn borer

  • Expect little or no benefit on Bt corn (especially the newer traits)

    • Exposure to insecticides without much yield reward

    • May create secondary pest problems (spider mites)

Take home about new bt corns
Take Home About New Bt Corns populations (Henry Co., TN)

University data indicates that the new Bt corn traits will not improve yields in most cases compared with the original Bt technologies

  • Benefit of reduced refuge requirement

  • Some potential for improved grain quality and reduced mycotoxins … but not close to a silver bullet

  • IRM ???

    • Corn borers – expect multiple Bt toxins to delay resistance

    • Corn earworm – exposure to multiple Bt toxins without much reward is concerning

Questions populations (Henry Co., TN)

War Eagle!

Aflatoxin levels in corn roy parker texas a m university 2011
Aflatoxin Levels in Corn populations (Henry Co., TN)Roy Parker, Texas A&M University, 2011

Test 1 Test 2

No statistically significant differences

Japanese beetles
Japanese Beetles populations (Henry Co., TN)

New Threshold: Treat when 3 or more beetles are present per ear during the first week of silking.

Infestations are usually worse along field margins.

Sugarcane beetles
Sugarcane Beetles populations (Henry Co., TN)

Final kernel d amage cm 2 ear in center two rows of plot
Final populations (Henry Co., TN)Kernel Damage(cm2/ear in center two rows of plot)

Early planting

Late Planting

P < 0.0045, LSD(0.05) = 0.094, CV = 61.9

P = 0.0428, LSD(0.05) = 0.054, CV = 80.4



cm2 damage

cm2 damage







Grain yield b a
Grain yield populations (Henry Co., TN)(B/A)

Early planting

Late Planting

P = 0.6439, LSD(0.05) = 16.7, CV = 6.4

P = 0.6860, LSD(0.05) = 8.5, CV = 2.8



Simulated cew feeding blister steckel et al
Simulated CEW Feeding (Blister) populations (Henry Co., TN)Steckel et al.

Tennessee corn isolines comparisons impact of new bt technologies vt3 pro smartstax viptera
Tennessee - Corn Isolines Comparisons populations (Henry Co., TN)Impact of New Bt Technologies (VT3 Pro, SmartStax, Viptera)

* Average of 3 (2008) or 2 hybrids (2009) that were VT Pro or SmartStax

Yield of selected seed trt s and in furrow combinations ms catchot
Yield of Selected Seed populations (Henry Co., TN)Trt’s and In-Furrow Combinations (MS, Catchot)

Non bt corn insecticide test moderate infestations of swcb application july 16 2008
Non-Bt Corn Insecticide Test populations (Henry Co., TN)Moderate infestations of SWCB (Application July 16, 2008)









Planted May 1