Redbacked cutworm (Euxoa ochrogaster ), Lepidoptera

Redbacked cutworm biology & life cycle

The redbacked cutworm can be found across the Prairie provinces, and is a pest of cereal and canola crops.

Eggs overwinter and hatch in the spring when soils warm. The larvae feed on plants during the night, and are inactive during the day. They feed for approximately 6-8 weeks. Mature larvae pupate in the soil.

Adults emerge in late July and August, and females lay eggs in weedy or fallow fields.

Identifying Redbacked cutworm

Redbacked cutworm: larvae

The young larvae hatch in early spring and are quite small (3 mm). Larvae moult five or six times and mature as round dull grey caterpillars. The larvae have two broad dull, red stripes along the length of their backs, a yellowish-brown head and measure approximately 38 mm (1.5") long.

Redbacked cutworm: Pupae

Pupae can be found in the soil in July; they are indistinguishable from other cutworm pupae.

Redbacked cutworm: adult

The adult redbacked cutworm 20 mm long with a wingspan of 40 mm. There are four colour varaitons of redback cutworm adults. Generally the forewing is reddish or light brown in colour while the hindwing is lighter in colour, often white. Adults are present during August and September.

Redbacked cutworm: management

Watch for damaged plants in June and July. Cutworms are nocturnal and hide during the day, making detection difficult. Inspect seedlings every 3–4 days during the first few weeks of crop development.
Focus scouting activity on south-facing slopes and hilltops. Soils are warmer and soil texture tends to be lighter, which is conducive to cutworm feeding activity.

Scouting:

Observe: Look for bare areas, holes and notches in foliage, and plants that are wilting, toppling over or completely cut off.
Dig: When notched, wilted, dead or cut-off plants are seen, dig around the roots (up to 4" deep) for cutworms.
Act: The economic threshold is 25–30% stand reduction. Patch spraying may be sufficient if concentrated to small areas.

Outbreak factors include:

Spring:
Warm and dry spring weather can increase the severity of damage from cutworms.

Summer:
Very dry soil during the larval stage increase cutworm behaviour and feeding habits. A hot, dry August also provides the best conditions for adult moth feeding.

Fall:
Cutworm moths lay several hundred tiny eggs on or just below the surface of loose, dry soil where they can comfortably overwinter.

Manage preventatively with seed treatment insecticides registered for cutworm. Foliar insecticide treatments may be warranted if economic thresholds are exceeded.

The following Management Practices* are recommended:

Natural biological enemies like parasitic insects, viral diseases and bacterial infections increase after year two of an infection and can reduce populations for at least two years.
Minimum tillage creates a greater diversity of cutworm species, but also of the natural parasites that keep populations in check.
Delaying seeding by 10–14 days may help reduce populations by starving young larvae populations.
Weed control in fallow fields is critical in late summer when cutworms are laying eggs.

*Source: Canola Council of Canada.