Beginner

Scientific Name
Striacosta albicosta

Identification

• Larvae are tan to pink
• 2 broad dark brown stripes on the pronotum (shield-like structure just behind the head)
  
• Adult moths have a white band running along the edge or margin of each wing and a spot or “moon” and boomerang-like mark

Often Confused With
Corn earworm
European corn borer

Period of Activity
The western bean cutworm has yet to be identified in Ontario. It is expected that the moths would begin to emerge in early July.

Scouting Notes
Begin scouting when the first moths are noticed and continue until after the moth population peaks. Scout 10 plants each at 10 locations in the field.

Thresholds
Insecticide should be considered when there are egg masses or small larvae in 8% of plants.

Advanced

Scientific Name
Striacosta albicosta

Despite its name, the Western Bean Cutworm (WBC) is a pest of corn (field, sweet and seed) as well as dry beans (with the exception of soybeans) and to a lesser extent tomatoes and nightshades. Unlike other cutworms, this pest prefers to feed on the fruit of the plant, i.e. corn ears and bean pods.

Identification
Adult WBC moths have a white band running along the edge or margin of the wing, a spot or "moon' and boomerang-like mark.

Larvae are tan to pink in colour. The only distinguishing marking WBC larvae have is on their pronotum, the shield-like structure just behind the head of the larvae. The WBC's pronotum has two broad dark brown stripes.

Often Confused With
Corn earworm
European corn borer

Biology
WBC overwinter in other regions as larvae in soil chambers. Adult moths emerge and are actively flying in late June, early July laying their eggs on the upper leaf surface of the upper leaves of the corn plants. Hybrids that hold their leaves upright are most preferred. Adults are attracted to fields in the whorl to pretassel stages of corn and only prefer the dry bean crop to lay their eggs in once the corn crop is in tassel or beyond. Eggs hatch within a week. Unfortunately the larvae are very mobile and can disperse from the original egg site to other plants in the vicinity so many plants can be impacted from one egg mass.

In corn, young larvae feed on the tassels and silks until they are large enough to tunnel into the ear and feed extensively on the kernels.

Period of Activity
The WBC has yet to be identified in Ontario. It is expected that the moths would begin to emerge in early July.

Scouting Notes
Begin scouting when the first moths are noticed and continue until after the moth population peaks. Scout 10 plants each at 10 locations in the field. Examine the upper surfaces of plant leaves for larvae or egg masses. Unlike other cutworms, WBC is not cannibalistic and therefore numerous worms can be found on a single ear of corn.

Thresholds
Insecticide should be considered when there are egg masses or small larvae in 8% of plants.

Management Notes

• Entry holes can sometimes be seen on the outside of the husk though they can also enter through the silk channels. Once they are in the ear control is impossible.
  
• Unfortunately western bean cutworms are not cannibals and therefore multiple larvae can feed on the same ear, leaving little left to harvest when infestations are high.
  
• Additional impact to quality can be expected from ear rots and secondary pests that may come in and feed on the damaged ears.
  
• Estimates on yield loss in corn from other jurisdictions indicate that a field infestation of one larva per ear can cause a 3.7 bu/ac loss.