Corn earworm
Corn earworm and tomato fruitworm are the same insect, Helicoverpa zea. In the north the moths do not survive the winter; they arrive on storm fronts from the south, in New England from mid-July to September. Females lay single eggs on fresh corn silk, or on tomato leaves near the flowers. In corn the larvae crawl down the silk channel and eat the kernels at the tip. In tomato they bore into green fruit and move from fruit to fruit. Once a larva is inside, nothing sprayed will reach it, so control depends on timing: treat the silks, or the eggs, before they hatch and burrow in.
A late-instar Helicoverpa zea feeding among kernels at the tip of a sweet corn ear. Photo: pending.
Identification
Full-grown larvae are 1½ to 2 inches (4–5 cm) long, with a golden-brown to orange head and light and dark stripes running along the body. The body colour varies widely: green, brown, tan, pink, yellow or nearly black. Numerous small black spines give the skin a rough feel, which separates it from the fall armyworm: that larva lacks the spines and does not feel rough. Young larvae are creamy white with black heads. As they grow they turn cannibal, so a corn ear usually ends up with only one mature larva.
The moth is light tan to olive or reddish-brown, with a wingspan of about 1–1¾ inches (25–45 mm; UF/IFAS gives 32–45 mm, UC IPM 1–1.5 in, UMass 1.2–1.5 in), a dark spot on each forewing and a dark band near the edge of the hind wing. Live moths have bright green eyes. The eggs are tiny, 0.5–0.6 mm across, ribbed and creamy white, and develop a reddish-brown ring after about a day. They are laid singly on fresh silk and on leaf hairs.
Easily confused with
- Fall armywormAlso a pestA white upside-down Y on the front of the dark head, and four dark spots in a square on top of the eighth abdominal segment, near the rear end. It also lacks the earworm's microspines, so it does not feel rough.
- European corn borerAlso a pestPale, with small dark spots on each segment rather than stripes, and a dark head. It tunnels into stalks as well as ears, entering the ear through the side or the tip; the earworm stays in the ear, feeding down the silk channel from the tip.
- Tomato pinworm (in tomato fruit)Also a pestLeaves a small, dry burrow under the calyx that does not go far into the fruit. The fruitworm chews large, deep holes, especially at the stem end.
Damage symptoms
Most of the damage is to sweet corn. Field corn tolerates far more. Young larvae feed on the silks at first, then work down to the kernels at the tip, and the damaged tip also attracts sap beetles. UMass puts sweet corn losses at up to 50% if the pest is not managed. In tomatoes the fruit is entered when it is 0.75–2 inches across, and damaged fruit ripens early.
- Kernels at the ear tip eaten, with moist frass under the husk
- Silks clipped off by young larvae
- Sap beetles crowding into damaged ear tips
- Tomato fruit with a hole at the stem end and a watery, frass-filled cavity
- Green tomatoes ripening early after being entered
Lifecycle & degree days
The pupa overwinters in the soil only as far north as about 40° N, roughly Kansas, Ohio, Virginia and southern New Jersey. Further north, every season starts with migrant moths. Generations range from one in the far north and two in the Northeast to four or five in Louisiana and southern California and perhaps seven in southern Florida. UC IPM gives 968 degree-days (°F) per generation, between thresholds of 55 °F and 92 °F. Numbers build as the season goes on, so late-planted corn gets the worst of it.
- Overwinters
- Pupa in soil, north to about 40° N; migrates further north
- Arrives (New England)
- Mid-July to September
- Generations / yr
- 1 far north; 2 Northeast; 4–5 Louisiana and southern California; up to 7 southern Florida
- Degree days
- 968 °F-days per generation (55 °F lower, 92 °F upper threshold)
- Larval feeding
- 14–16 days (Kentucky) to 3–4 weeks (UMass)
Host crops
Corn is the preferred host, and moths are strongly drawn to fresh silk. UF/IFAS lists a long run of other vegetables, including tomato, pepper, eggplant, beans, lettuce, cabbage, melons, okra, squash and potato. The other names, cotton bollworm and sorghum headworm, come from the field crops it attacks.
Monitoring & action thresholds
Commercial sweet corn growers use pheromone trap catches to set spray intervals. UMass skips spraying at fewer than 1.4 moths a week and shortens the interval to 3 days at more than 91 a week. Kentucky sets its bands higher: no spray below 5 moths a week, a 3-day interval only above 349. For processing tomatoes, UC IPM samples the leaf below the highest open flower on 30 plants and takes a second sample if there are 3 or more healthy white eggs. None of these applies to a few garden plants.
In corn, start watching when the silks appear. Large numbers of eggs on fresh silks signal a potentially damaging population, according to UC IPM. Kentucky's spray window runs from when 10% of ears are silked until 90% of the silks have wilted. In tomatoes, search the leaves near the top flowers for single, ribbed white eggs; a reddish ring means they are about to hatch, and black eggs have been parasitised. Pick off and destroy entered fruit.
Biological control
Corn earworm eggs are laid singly and exposed, which makes them the weak stage. Trichogramma wasps parasitise them, turning them black, and UC IPM treats releases of T. pretiosum as a biological control option in tomato. Minute pirate bugs (Orius), lacewings, damsel bugs and big-eyed bugs eat eggs and small larvae, and braconid wasps such as Cotesia and Microplitis croceipes parasitise the caterpillars. UF/IFAS is candid, though: natural enemies usually do not cause high earworm mortality or prevent crop injury, and UC IPM warns that released Trichogramma are not always effective. Bt works only before the larvae enter the ear or fruit; the Thuricide home label claims suppression only on tomato fruitworm. UF/IFAS also notes that commercially available insect-killing nematodes applied to corn silk give good suppression of developing larvae, which it says suits home gardens rather than commercial fields.
Cultural controls
Timing and a barrier on the silk channel are what work in a garden.
- Plant sweet corn early: early plantings need fewer treatments, because earworm numbers rise through the season
- Put 0.75–1.0 ml (about 0.03 fl oz) of mineral oil on the silks of each ear five to seven days after silking
- Grow Bt sweet corn varieties where available; resistance is increasingly reported, so they may still need help late in the season
- Till or dig the soil in autumn to reduce overwintering pupae
- In tomatoes, pick and destroy entered fruit so the larvae do not move on to the next one
Chemical, last resort
- Bt kurstakiREI 4 h
- MethoxyfenozideREI 4 h
- SpinosadREI 4 h
- ChlorantraniliproleREI 4 h
Sources
UF/IFAS EDIS EENY-145, Corn Earworm, Helicoverpa zea (Capinera)
UC IPM Pest Management Guidelines: Tomato — Tomato Fruitworm (Natwick et al., 12/13)
UC IPM Pest Management Guidelines: Corn — Corn Earworm (Godfrey et al., 08/2008)
UC IPM, Relative Toxicities of Insecticides Used in Tomatoes to Natural Enemies (09/16)
UMass Extension Vegetable Program, Corn Earworm (updated 2018)
Univ. of Kentucky ENTFACT-318, Corn Earworm Management in Sweet Corn (Bessin, rev. 1/26)
Bonide Thuricide concentrate label, EPA Reg. 4-226 (2016)
DiPel DF label, EPA Reg. 73049-39 (2022)
UF/IFAS EDIS EENY-098, Fall Armyworm (Capinera)
Univ. of Kentucky ENTFACT-110, Fall Armyworm in Corn
UMass Extension Vegetable Program, European Corn Borer
UC IPM Pest Management Guidelines: Tomato — Tomato Pinworm
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →Corn earworm by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.