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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

Relative Efficacy of Corn IST

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

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
  • 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
  • Triggers scouting or spray
new southwestern corn borer threshold non bt corn
New Southwestern Corn Borer Threshold(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 SelectionRefer 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 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

Relative Efficacy of Selected Bt Corn Traits

(see handout for more inclusive list & refuge requirements)

non bt corn refuge requirements
Non-Bt Corn Refuge Requirements
  • 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?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

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


SWCB and ECB InjuryCM 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






Leaf Injury Score for FAW Catchot, 2010, Starkville, MS

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








Optimum Intrasect



Corn Earworm

The most common ear feeding caterpillar

smartstax test 2009
SmartStax Test - 2009





smartstax test 2010
SmartStax Test - 2010


VT3P or SS


Approximate Reduction in Kernel Damage Compared with Non-Bt Corn(Summarized Across Multiple University Trials, Corn Earworm)

Reality Check

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

insecticide trial on non bt corn corn earworm injury and yield tn 2011
Insecticide Trial on Non-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-Bt Corn(Tennessee, Stewart, 2012)

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

spraying corn for corn earworm
Spraying Corn for Corn Earworm

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

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

War Eagle!

aflatoxin levels in corn roy parker texas a m university 2011
Aflatoxin Levels in Corn Roy Parker, Texas A&M University, 2011

Test 1 Test 2

No statistically significant differences

japanese beetles
Japanese Beetles

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.

final kernel d amage cm 2 ear in center two rows of plot
Final 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 (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



tennessee corn isolines comparisons impact of new bt technologies vt3 pro smartstax viptera
Tennessee - Corn Isolines ComparisonsImpact of New Bt Technologies (VT3 Pro, SmartStax, Viptera)

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

non bt corn insecticide test moderate infestations of swcb application july 16 2008
Non-Bt Corn Insecticide TestModerate infestations of SWCB (Application July 16, 2008)









Planted May 1