Armyworm
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Injury to Corn
- Armyworm larvae feed only on the leaf margins; they do not tunnel into the stalk or feed in the ear
- Severe defoliation (below) removes the softer leaf tissue, leaving only the stalk and tougher leaf midribs
- Plants will recover from moderate levels of injury unless the growing point has been damaged
- Field-wide defoliation may occur if the population is large, which is most likely in fields with weedy grasses
Armyworm Identification
- Adult moth is pale gray to pale brown, with a white speck in the center of each front wing
- Larva
- 1½ inches long when full grown with 2 “orange” stripes alongside and 2 dark stripes on back
- 4 pair of abdominal legs often have a lateral dark bar (see arrow in photo below)
- Head with 2 vertical bars on face (see photo below)
- Similar species
- Fall armyworm has black “warts” on back
- Corn earworm has black “warts” on back; lacks dark bars on legs and dark bars on face
Left to right: armyworm, fall armyworm and corn earworm.
Pest Status
- Armyworm is an uncommon pest in corn
- Economic damage is rare in conventionally-tilled fields
- Injury most commonly occurs in reduced-tillage fields with grassy weeds or a grass cover crop
- Moths lay eggs on grasses before corn is planted, then when a herbicide is used to kill the grass, the larvae move to the young corn plants
- Larvae also will migrate from adjacent cereal small grains when that crop approaches maturity
Armyworm Facts and Impact on Corn
- Scientific name: Mythimna unipuncta
- Former name: Pseudaletia unipunct
- Common name: armyworm
- Often incorrectly called “true” armyworm
- Common name relates to behavior of larvae crawling in large numbers from one area to another, often defoliating plants as they migrate
- Importance
- Larvae feed primarily on wild and domestic grasses, including corn, bluegrass, timothy, cereal small grains, and foxtail
- Late-stage larvae may defoliate vegetative-stage corn, especially along field edges or in areas with grassy weeds
Injury to corn from armyworm in southern Iowa.
Armyworm Life History
- Pupae overwinter in soil in southern climates
- Adults migrate north in April and May and lay eggs in clusters on lower leaves of grasses or small grains
- Eggs hatch in 1-2 weeks depending on temperature
- Larvae feed mostly at night or on overcast days; during sunny days they may remain hidden in ground litter or behind leaf sheaths
- Because adults are migratory and flight is strongly dependent upon weather fronts, injury is sporadic in an area from 1 year to the next
- There are 2-3 generations per year, but rarely in the same fields
Integrated Pest Management of Armyworm
- Transgenic Bt corn
- Pioneer® brand corn products with Optimum® Leptra® insect protection provide excellent control of 1st to 3rd stage larvae
- Pioneer brand corn products with Optimum® Intrasect® insect protection provide very good control of 1st to 3rd stage larvae
- Weed Management
- Weedy grasses should be burned down with a herbicide at least 7 days before corn emergence
- Herbicides applied to weedy grasses after corn emerges should be tank mixed with an insecticide
- Field Scouting
- Corn adjacent to small grain crops should be scouted along field borders for migrating armyworms as the cereal crop matures
- Insecticides
- Liquid insecticides should be applied to corn if larvae are less than 1½ inches long and significant defoliation is occurring; larvae longer than 1½-inch are nearly done feeding and an insecticide will be of limited value
Author: Marlin E. Rice
Reviewer: Herb Eichenseer
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YGCB,HX1,LL,RR2 (Optimum® Intrasect®) - Contains the YieldGard® Corn Borer gene and Herculex® I gene for resistance to corn borer. |
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| AVBL,YGCB,HX1,LL,RR2 (Optimum® Leptra®) - Contains the Agrisure Viptera® trait, the YieldGard Corn Borer gene, the Herculex® I gene, the LibertyLink® gene, and the Roundup Ready® Corn 2 trait. Agrisure® and Agrisure Viptera® are registered trademarks of, and used under license from, a Syngenta Group Company. Agrisure® technology incorporated into these seeds is commercialized under a license from Syngenta Crop Protection AG. Herculex® I Protection technology by Dow Agro Sciences and Pioneer Hi-Bred. Herculex® and the HX logo are registered trademarks of Dow AgroSciences LLC. YieldGard®, the YieldGard Corn Borer Design and Roundup® Ready are registered trademarks used under license from Monsanto Company. Liberty®, LibertyLink® and the Water Droplet Design are trademarks of Bayer. |
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary.
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