CORN EARWORM: Helicoverpa zea, Noctuidae

ADULT: Wing color is sex dependent. Female fore wings are more yellow to pinkish-brown, while those of males are more light greenish-brown. There is usually a dark spot in the middle of the fore wing (reniform spot). Both fore and hind wings have dark margins and the hind wings have a short, narrow band near the middle with two pale spots near the edge of the wing in the dark margin. Both sexes have a wingspan of 1 1/2 in.

EGG: Deposited on leaves singly or in small groups of less than five, the eggs are not protected by scales. Eggs have visible ridges running from top to bottom. Larvae emerge from eggs in 3 to 4 d.

LARVA: Newly emerged larvae are translucent white to yellow with a light brown head. Older larvae vary considerably from dark yellow to green to tan to dark brown. Mature larvae can reach 2 in.  Larvae have three pairs of true legs and five pairs of prolegs.  The skin (cuticle) of larvae are covered with microspines. The dark colored tubercles (larger bumps) on abdominal segments 1, 2 and 8 do not have microspines more than 1/4 the way to their apex. The central area on the inside surface of the mandibles do not have a separate toothed area.

PUPA: The pupae are reddish-brown in color, 3/4 in. long, and are found in soil. Adults emerge in 7 to 10 d.

GENERATION TIME: 28 to 40 d.

DAMAGE: Young larvae feed between leaf veins often on outer portions of leaves before moving into the whorl to feed on young leaves. Larger larvae can completely consume the growing point of the plant and severely damage the tassel before it emerges from whorl. More commonly it attacks the ears causing severe damage to silk, kernels and cob. Twenty years ago this was the primary pest of corn throughout Florida. Fall armyworm has largely replaced it as the primary pest, particularly in central and southern Florida, but it still causes severe damage in corn fields throughout the state. Corn grown in northern Florida counties during the late spring and summer is more likely to have large populations of H. zea.

CONTROL: Birds and insect natural enemies aid in earworm control, but generally do not exert enough pressure to prevent yield loss, particularly in sweet corn. Host plant resistance is emerging as an effective control strategy against earworms in both field and sweet corns. Varieties with insect enzyme inhibitors and new bioengineered corns with bacterial toxins will help to greatly reduce earworm feeding pressure. Pesticidal controls are most effective against the younger instars with higher rates and more frequent applications needed to try to control later instars. Control of neonate larvae emerging on ears is important to prevent economic damage. Fields should be scouted at least twice weekly for eggs and first instar larvae during the ear stage to detect and control populations before they cause economic damage. Thresholds used during this period range between 2 and 8%, with estimates at the high end eliciting more frequent sampling. Available pesticides are used as broadcast or banded sprays. Pesticides should be applied before larvae can penetrate into the ears. Formulations, rates, and pre-harvest intervals of insecticides labeled for corn earworm control in Florida are listed below for sweet corn (Table 1) and field corn (Table 2).

Table 1.  Chemical control of corn earworms in sweet corn
Insecticide, formulation Rate/acre Min. days to harvest Application notes
carbaryl (Sevin, Sevin XLR Plus) 4 F, 4 EC 1 - 2 qt 2 ears; 48 forage; 14**  
carbaryl (Sevin) 80 WSP 1.25 - 2.5 lb 2 ears; 48 fodder; 14**  
chlorpyrifos (Lorsban) 4 E 1.5 - 2 pt 21  
cyfluthrin (Baythrioid 2) 2 EC 1.6 - 2.8 fl oz 0  
cyhalothrin (Karate, Warrior) 1 EC 2.56 - 3.84 fl oz 1  
diazinon (D-z-n) 50 W 2 - 2.5 lb 7  
diazinon (D-z-n AG500) 4 EC 1 - 1.25 qt 7  
diazinon (D-z-n AG600) WBC 25.5 - 32  fl oz 7  
endosulfan (Phaser, Thiodan) 3 EC 2 qt 1; do not feed to livestock fresh use only
endosulfan (Phaser 50 WSB, Thiodan 50 WP) 3 lb 1; do not feed to livestock fresh use only
endosulfan (Thiodan Cottonseed Oil) 3 qt 1; do not feed to livestock fresh use only
esfenvalerate (Asana XL) 0.66 EC 5.8 - 9.6 fl oz 1  
ethyl parathion (Parathion) 8 EC 0.5 pt 12  
methomyl (Lannate LV) 2.4 EC 0.75 - 1.5 pt 0 ears; 3 forage earworm
methomyl (Lannate SP) 90 WSP 0.3 - 0.5 lb 21 ears, fodder; 3 forage earworm
methomyl 5 G 3 lb 3 forage, grazing banded by ground only
oil (Sun Spray) 7 E 2 gal / 100 gal water   early spring, summer, earworm
permethrin (Ambush) 2 EC 6.4 - 16.0 fl oz 1  
permethrin (Ambush)  25 WP 6.4 - 16.0 oz 1  
permethrin (Pounce) 25 WP 6.4 - 12.8 oz 1  
permethrin (Pounce) 3.2 EC 4 - 8 fl oz 1  
permethrin (Pounce WSB) 24.7% WSB 6.4 - 12.8 oz 1  
thiodicarb (Larvin) 3.2 EC 20 - 30 fl oz 0 ears; do not feed to livestock  
**harvest or grazing of forage or silage


Table 2.  Chemical control of corn earworms in field corn
Insecticide, formulation Rate/acre Min. days to harvest Application notes
carbaryl (Sevin, Sevin XLR Plus) 4 F, 4 EC 1 - 2 qt 48 fodder, grain; 14**  
carbaryl (Sevin) 80 WSP 1.25 - 2.5 lb 48 fodder, grain; 14**  
chlorpyrifos (Lorsban) 4 E 1.5 - 2 pt 35 fodder, grain; 14 grazing, silage  
cyhalothrin (Karate, Warrior) 1 EC 1.92 - 3.20 fl oz 21  
esfenvalerate (Asana XL) 0.66 EC 5.8 - 9.6 fl oz 21  
ethyl parathion (Parathion) 8 EC 0.5 pt 12  
methomyl 5 G 3 lb 3 grazing or feed plants banded by ground only
methomyl (Lannate LV ) 2.4 EC 0.75 - 1.5 pt 3 forage; 21 ears, fodder  
methomyl (Lannate SP) 90 WSP 0.25 - 0.5 lb 3 forage; 21 ears, fodder  
oil (Sun Spray) 7 E 2 gal / 100 gal water   early spring, summer
permethrin (Ambush) 2 EC 6.4 - 12.8 fl oz 30 harvest of fodder, grain  
permethrin (Ambush) 25 W 6.4 - 12.8 oz 30 harvest of fodder, grain  
permethrin (Pounce) 25 WP 6.4 - 12.8 oz 30 harvest of fodder, grain  
permethrin (Pounce) 3.2 EC 4 - 8 fl oz 30 harvest of fodder, grain  
permethrin (Pounce WSB) 24.7% WSB 6.4 - 12.8 oz 30 harvest of fodder, grain  
**harvest or grazing of forage or silage