University of Delaware IPM Program Joanne Whalen, Extension IPM Specialist
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%
