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Sweet Corn Scouting Guidelines - 2003
University of Delaware IPM Program
Joanne Whalen, Extension IPM Specialist
Marty Spellman, Extension IPM Associate

I. Plant Emergence Until Tassles Visible:
  • Examine 10 consecutive plants in 10 locations for the presence of insect feeding damage for a field up to 50 acres in size; Add one additional sampling site for each additional 10 acres
Pest Species
When to Sample
Action Threshold
Flea Beetle Emergence to 6-Leaf Stage 5 % of the plants infested
Cutworms Emergence to 6-Leaf Stage 1-2 leaf stage: 10% of plants with feeding or 3 % cut plants and larvae present

3-4 leaf stage: 5% plants cut and larvae present
European Corn Borer Early Whorl to Tassel Emergence-mainly a problem in early planted corn Early Season Varieties/Super Sweets/Sugar Enhanced: 15% plants infested

'Silver Queen Type': 30% plants infested
Fall Armyworm Emergence to Pretassel - early detection critical when worms are small; mainly a problem in late planted corn 12 - 15 % plants infested and worms less than one inch long - multiple applications may be needed
Sap Beetle Tasseling to Harvest 5% plants infested
Corn Leaf Rust Late June - Early July - emergence to late whorl note presence and absence esp on susceptible varieties



II. First Ear Shanks Visible Until Harvest :

  • The decision to treat is based on blacklight and pheromone trap catches. The first sprays should be applied when ear shanks are visible -- once silk is present worms may already be in the ears.

Action Thresholds for Silk Stage Sweet Corn:

A. Based on Corn Earworm Blacklight Trap Catches (conservative system)
Number of Moths Caught per Seven Days Silk Spray Schedule
<1 No Spray
1 6 day
2 5 day
3 4 day
4-30 3 day
>30 2 day



B. Based on Corn Earworm Pheromone Trap Catches

  • Generally used as a guideline in combination with light trap information. Requires use of a wire mesh trap and Hercon CEW pheromone lure placed with the base of the trap at silk height in fresh silking corn. Check traps 3 times per week throughout the growing season.
Number of Corn Earworm Moths Caught
Per day Per 5 days Per week Spray Interval
<0.2 <1 <1.4 No Spray
0.2-0.5 1.0-2.5 1.4-3.5 6 day
0.5-1.0 2.5-5.0 3.5-7.0 5 day
1.0-13.0 5.0-65.0 7.0-91.0 4 day
>13.0 >65.0 >91.0 3 day


    • In some cases corn earworm catches are very low; however, corn borer and fall armyworm pressure is high. If no sprays are called for CEW, the following spray schedule should be used:
Corn Borer/Fall Armyworm/Sap Beetle Spray Schedule
ECB light trap catch is >100 per 5 days 4 day
ECB light trap catch is 51-100 per 5 days OR FAW infestations in whorl stage is >30% OR sap beetle infestation is > 10% 5 day
ECB light trap catch is 25-50 per 5 days & FAW infestations in whorl stage is <30% & sap beetle infestation is < 10% 6 day
ECB light trap catch is <25 per 5 days & FAW infestations in whorl stage is <30% & sap beetle infestation is < 10% No Spray