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.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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|
various products # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
11A |
Label rates | 4 | 0 | This material may be less effective tha... | narrow | low | low | low | none | — | — | — | — | — | 08/2008 | ||
|
|
Asana XL | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
5.8–9.6 fl oz | 12 | See comments | Do not exceed 0.25 lb a.i./acre/season o... | broad | high | moderate | high | moderate | high | intermediate | extra high | low | intermediate | 08/2008 | ||
| Lannate SP | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
1A |
0.25–0.5 lb | 48 | See label | Certain varieties of sweet corn may be i... | broad | high | high | high | moderate | — | — | — | — | — | 08/2008 | |||
|
|
Pounce 3.2EC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
4–8 oz | 12 | See comments | For field corn, popcorn, and field corn... | broad | low | high | high | long | intermediate | low | extra high | very low | intermediate | 08/2008 | ||
|
|
Radiant SC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
3–6 fl oz | 4 | See comments | Preharvest interval for sweet corn and... | narrow | low | moderate 13 | low/moderate | moderate 14 | low | low | low | very low | low | 08/2008 | ||
|
|
Entrust # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
1–2 oz | 4 | See comments | Apply as a broadcast or as a directed sp... | narrow | low | moderate 13 | low/moderate | short to moderate 13 | very low | low | low | very low | low | 08/2008 | ||
|
|
Success | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
3-6 fl oz | 4 | See comments | Apply as a broadcast or as a directed sp... | narrow | low | moderate 13 | low/moderate | short to moderate 13 | very low | low | low | very low | low | 08/2008 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- * a Permit required from county agricultural commissioner for purchase or use.
- # a b Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 a b c d e Toxic to some natural enemies (lacewing and syrphid fly larvae, predatory beetles, and thrips) when sprayed and up to 5 to 7 days after.
- 14 ↩ Residual is moderate if solution is between a pH of 7 and 8.
UC IPM Pest Management Guidelines: Corn
UC ANR Publication 3443
L.D. Godfrey, Entomology, UC Davis
S.D. Wright (emeritus), UC Cooperative Extension Tulare and Kings counties
C.G. Summers (emeritus), Entomology, UC Davis and Kearney Agricultural Research and Extension Center, Parlier
C.A. Frate (emeritus), UC Cooperative Extension Tulare County
Acknowledgement for Contributions to Invertebrates
M.J. Jimenez (emeritus), UC Cooperative Extension Tulare County
