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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Color variations of tomato fruitworm (also called corn earworm and cotton bollworm).

Corn

Corn Earworm

Scientific name: Helicoverpa zea

(Reviewed 1/06, updated 8/08)

In this Guideline:

DESCRIPTION OF THE PEST

Corn earworm moths are most active during evening and night. They are about 0.75 inch long, rather robust, with a wing span of 1 to 1.5 inches, and adults range from olive green, to tan, to dark reddish brown in color. Egg laying occurs throughout the sweet corn growing season. The tiny, white eggs are laid singly on the foliage and fresh corn silk, which is the favorite site for egg deposition. After about a day, eggs develop a reddish brown ring in the top portion. Eggs are spherical with 12 or more ridges radiating from the top. Young larvae are greenish with black heads and conspicuous black hairs on the body. Fully developed worms are about 1.5 inches long and range in color from pale green or pinkish to brown.

DAMAGE

The corn earworm may be present throughout the season but is most abundant during August and September. Larvae feed on leaves, tassels, the whorl, and within ears, but the ears are the preferred sites for corn earworm attack. Ear damage is characterized by extensive excrement at the ear tip. Young larvae feed on corn silks, clipping them off. Shortly thereafter, they feed their way into the ear where they remain, feeding in the tip area until they exit to pupate in the soil.

MANAGEMENT

Corn earworm is primarily a problem in sweet corn where treatments should be timed to coincide with egg hatch.

Biological Control
Many predators and parasites attack corn earworm eggs, including several species of Trichogramma. Most parasitized eggs turn black, but there may be a lag period before they do so. General predators such as lacewings, minute pirate bugs, and damsel bugs feed on corn earworm eggs and small larvae.

Cultural Control
In sweet corn, very early plantings require fewer treatments than late-season corn because earworm population densities increase as the season progresses.

Organically Acceptable Methods
Biological and cultural controls and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on an organically grown crop.

Monitoring and Treatment Decisions
Insecticidal control of corn earworm is difficult and depends on proper timing and thorough coverage. Begin sampling soon after corn emergence but pay particular attention to corn that is silking in late summer/early fall. The presence of large numbers of eggs on fresh corn silks indicates the potential for damaging populations. Eggs hatch in 5 to 7 days following oviposition. Once larvae enter the corn ears, control with insecticides is difficult. Direct insecticidal control towards young larvae that are feeding on the exposed ear tips. Treatments are usually not needed on field or silage corn. In sweet corn, where tolerance for worm damage is low, timing of insecticide treatments is critical: begin treatments during silking stage, at the start of egg hatch. Apply additional treatments if they are necessary.

Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, information related to natural enemies and honey bees and environmental impact.
 
A. SPINOSAD
  (Entrust)# 1–2 oz 4 Sweet, popcorn, seed:
1 - grain; 7 - forage
  (Success) 3–6 fl oz 4 Field corn: 7 - forage; 2
8 - grain, fodder
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Apply as a broadcast or as a directed spray with adequate spray volume and pressure to ensure thorough wetting of silk.
 
B. SPINETORAM
  (Radiant) SC 3–6 fl oz 4 see comments
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Preharvest interval for sweet corn and seed corn harvested for grain is 1 day and 3 days when harvested for forage and fodder; for field corn, teosinte, and popcorn it is 28 days for grain harvest and 3 days for forage and fodder.
 
C. METHOMYL*
  (Lannate SP) 0.25–0.5 lb 48 see label
  MODE OF ACTION: A carbamate (Group 1A)1 insecticide.
  COMMENTS: Certain varieties of sweet corn may be injured by methomyl.
 
D. ESFENVALERATE*
  (Asana XL) 5.8–9.6 fl oz 12 Seed corn/Popcorn: 1
        Field corn: 21
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Do not exceed 0.25 lb a.i./acre/season on field corn and seed corn or 0.5 lb a.i./acre/season on popcorn.
 
E. PERMETHRIN*     Grain or fodder: 30
  (Pounce) 3.2EC 4–8 oz 12 Sweet corn: 1
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: For field corn, popcorn, and field corn grown for seed and sweet corn. Apply before brown silk stage.
 
F. CHLORPYRIFOS*     Grain or ears: 21
  (Lorsban) 4E 1.5–2 pt 24 Grazing or silage: 14
        Livestock feed: 35
  MODE OF ACTION: An organophosphate (Group 1B)1 insecticide.
  COMMENTS: For field corn and sweet corn (including corn grown for seed); not for use on popcorn. Apply as a broadcast spray. Avoid drift and tailwater runoff into surface waters.
 
G. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: This material may be less effective than broad-spectrum insecticides, but it does not destroy natural enemies of corn earworm. Control is maximized by thorough coverage and by making applications when larvae are small.
 
** Mix with sufficient water to obtain full coverage.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown produce.
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Corn
UC ANR Publication 3443
Insects and Mites
L. D. Godfrey, Entomology, UC Davis
S. D. Wright, UC Cooperative Extension, Tulare County
C. G. Summers, Kearney Agricultural Center, Parlier
C. A. Frate, UC Cooperative Extension, Tulare County
Acknowledgement for contributions to Insect and Mites:
M. J. Jimenez, UC Cooperative Extension, Tulare County

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