Pest Profile: Western Bean Cutworm

(Striacosta albicosta)

Pest Profile

26 March, 2025

3 min read

General Overview:

Native to the Grain Plains region of the US, WBC migrated into the US corn belt in the early 2000s
The moths seek out dry beans or corn to lay their eggs, which hatch into crop damaging larvae
WBC populations continue to move, and are now found in major corn growing regions of Eastern Canada

Description and life cycle:

Moths emerge from over wintering burrows between late June and early August
Adult moths are brownish/tan in colour, 2 cm long, with a distinctive paler circle on each wing
Following breeding, females seek out suitable crops (dry beans or corn) to lay their eggs
Egg masses, of 50-100 eggs, are initially white, darkening over time before hatching 5-7 days later
Larvae emerge with a dark head, which lightens over the 6 developmental instars
From the 4^th instar onwards the ‘worms’ are a pale brown, with dark longitudinal stripes on each side of the body
The larvae feed on plant tissue, chewing into dry bean pods and the ears of corn
Crop damage is associated with yield loss from the feeding, but also quality losses from disease (ie. ear molds) that can infect the entry points
The 6^th instar the larvae will drop to the soil and form underground burrows to over winter
Overwintering success is much higher on sand soils (better drainage), and the following spring (May) the larvae will pupate to later emerge as adult moths
There is only one generation per season
Adults tend to stay close to where they emerge, but can be carried far from their overwintering sites due to prevailing winds

Crop Damage:

Only the larval stage of WBC damages crops
Feeding on flowers and pods in dry beans, or developing kernels in corn ears, decreases the harvestable yield, but more impactful are the diseases that can infect feeding damaged vegetation
Ear molds in corn, including those associated with mycotoxins that limit the utility of the grain, can be extremely impactful

Economic Thresholds:

In dry beans, pheromone traps should be placed near production fields. Traps with >50 moths would suggest those fields are at risk of damage from WBC and should be scouted. No thresholds are set for dry beans in Canada, but spraying an insecticide at the first signs of pod feeding has proven successful
In corn, pheromone traps can be utilized to determine when to scout (when noticeable moth populations are found). If scouting finds eggs masses on 5% or more of corn plants an insecticide spray is likely warranted

Control Strategies:

Crop scouting is the most crucial action step, to ensure action is only taken when necessary
If WBC is present at levels believed to be economically damaging, insecticides can be applied for control
In corn there are transgenic traits that can provide protection

**ADAMA's Portfolio for Western Bean Cutworm:**
ADAMA Product	Registered Crops Impacted By WBC
SILENCER^® 120 EC (Contact)	Dry beans and multiple other legume crops (refer to the label for full list)
ZIVATA^® (Contact)	Dry beans and multiple other legume crops (refer to the label for full list)
COSAYR^® (ingestion)	Corn (field, pop, sweet, seed), dry beans and numerous other legume vegetables (refer to the label for the full list)

Reference Literature: