Western Bean Cutworm

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Written by Mark Jeschke, Ph.D., Pioneer Agronomy Manager

Key Points

  • Pioneer conducted a nitrogen rate by crop rotation study in which nitrogen rate treatments were applied in the same locations of the field over multiple years.
  • Corn grown in rotation with soybeans was generally able to yield better under reduced nitrogen rates than corn grown continuously.
  • Yield of rotated corn with no applied nitrogen gradually recovered over time, with almost no yield loss observed after the 10th year of the study. This outcome is unusual and the reason for it is unknown.

Pest Facts and Impact on Crop

  • Species name: Striacosta albicosta.
  • Major larval feeding coincides with the ear development.
  • Direct feeding on the ears reduces grain yield.
  • Infestations of several larvae per ear can reduce grain yield up to 15-20%.
  • Feeding may allow mold and other fungal spores to colonize the ear, further reducing grain quality and potentially producing mycotoxins.
  • Larvae are pests of dry beans in the western U.S. and Great Lakes region, and of corn in the Corn Belt.

Approximate Range of Western Bean Cutworm

Geographic range of the western bean cutworm in the US.

Western bean cutworm historically occurred in cornfields of the Great Plains but has moved into the central and eastern Corn Belt.

Pest Symptoms

  • Leaf and whorl feeding by small stage larvae.
  • Ear penetration and kernel damage by large stage larvae.
  • Secondary infestation by ear molds after protection from shuck covering has been breached.

Damage from western bean cutworm

Damage from western bean cutworm.

Feeding by western bean cutworm and damage to ears

Feeding by western bean cutworm and damage to ears.

Feeding by western bean cutworm and damage to ears

Pest Identification

  • Western bean cutworm: No straight, lateral lines or black tubercles (warts) along the sides.
  • Fall armyworm: Thin white lines down middle of back and four large, dark tubercles on “tail” section.
  • Corn earworm: Lateral, thick pale stripe and dark tubercles.

Western Bean Cutworm

Western Bean Cutworm

Fall armyworm

Fall Armyworm

Corn Earworm

Corn Earworm

Integrated Pest Management

  • Populations: Several factors may contribute to increased populations, including mild winters, reduced use of foliar insecticides in corn, and reduced or no tillage.
  • Trapping: Use pheromone traps to determine when to start scouting for eggs; usually during VT-R2 stages.
  • Scouting: Check the upper flag leaf for egg masses after traps indicate moth flight; check 40 plants per field.
  • Ear molds: If ear molds are a problem, timely harvest and drying may be desirable to prevent mycotoxin formation.

In-plant Protection


  • Time application to coincide with egg hatch.
  • Larvae must come into contact with the insecticide before entering the ear. When larvae enter the ear, they are less likely to encounter the insecticide and control will be reduced.
  • Protection is most effective when egg hatch occurs during pollination.
  • When egg hatch occurs at brown silk stage or later, the larva can move quickly to the ears since fresh pollen is not available on which to feed.

Insecticide Treatment Threshold

  • Multiple extension organizations recommend treatment when 5% of plants have egg masses and/or young larvae.
  • Growers may consider treatment at lower infestation levels if:
    • The field has a history of economic damage from western bean cutworm.
    • DON levels in grain are a concern for the grower.

Western Bean Cutworm Annual Lifecycle in Corn

Western Bean Cutworm Annual Life Cycle in Corn

Herculex I  AcreMax Leptra  Leptra  Agrisure Viptera    Roundup Ready Corn 2

AML - Optimum® AcreMax® Leptra® products with AVBL, YGCB, HX1, LL, RR2. Contains a single-bag integrated refuge solution for above-ground insects. In EPA-designated cotton growing countries, a 20% separate corn borer refuge must be planted with Optimum AcreMax Leptra products. Agrisure Viptera® is a registered trademark 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. Liberty®, Liberty Link® and the Water Droplet Design are trademarks of BASF. Roundup Ready® is a registered trademark used under license from Monsanto Company.

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. Pioneer® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.