Western Bean Cutworm
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.
Western bean cutworm historically occurred in cornfields of the Great Plains, but has moved into the central and eastern Corn Belt.
- 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.
- Western bean cutworm: No straight, lateral lines or black tubercles (warts) along the sides.
- Fall armyworm: Thin white lines down middle of back and 4 large, dark tubercles on “tail” section.
- Corn earworm: Lateral, thick pale stripe and dark tubercles.
Western Bean Cutworm Annual Life Cycle in Corn
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.
- Due to various factors, including pest pressure, reduced susceptibility, and insect resistance in some pest populations, for the 2018 planting season and beyond, all references to control or suppression of western bean cutworm are being completely removed from bag tags, competitive trait tables, product use guides and other customer facing materials for products that include the Herculex® I (HX1) trait, but lack another effective mode of action for western bean cutworm.
- However, Pioneer® brand Optimum® Leptra® and Optimum® AcreMax® Leptra® insect protection provide an effective mode of action for in-plant protection against western bean cutworm.
Insecticides: Time application to coincide with egg hatch.
- 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.
Economic thresholds: A foliar insecticide should be considered if the percent of infested plants is reached or exceeded, based on crop value ($/bu) and management costs ($/acre).
Source: University of Nebraska. Thresholds based on yield of 220 bu/acre, 30,000 plants/acre, 85 eggs/mass, and 8% larval survival.