Pale western cutworm (Agrotis orthogonia), Lepidoptera

Pale western cutworm biology & life cycle

Pale Western Cutworm adults are present in August and September, and they lay eggs in loose, dusty soil. The Eggs overwinter and hatch in the spring when the larvae feed on early seedlings. Mature Larvae burrow into the soil to pupate by the end of June.

The pale western cutworm causes damage by cutting small holes in the leaf while it is still underground. The damages leaf becomes visible as it emerges. Larvae move along the row, cutting off leaves or entire plants. Older plants may be weakened and can lodge easily.

Identifying Pale western cutworm

Pale western cutworm: larvae

Larvae are colourless and about 3 mm (0.12") long. Fully-grown larvae have a yellow-brown head, are greyish-white to green in colour, and vary in length from 30–60 mm (1.2–1.4") long.

Larvae are the significant stage of this insect for crop damage. Larvae feed on emerging shoots and furled leaves of young plants, causing holes in the leaves. Older larvae can cause enough damage that plants are severed just below the soil surface. Occasionally severed plants are pulled and eaten underground.

Pale western cutworm: Pupae

About 20 mm long and indistinguishable from other cutworm pupae.

Pale western cutworm: adult

Pale western cutworm adult moths are 19 mm long with a wingspan of 38 mm. Adults are greyish white to brownish white, with several distinct cross lines and two or three spots on the forewing. The hind-wing is white in colour with an outer margin of grey or brown.

Pale western cutworm: management

Check for the presence of gaps within rows of germinating crop, which can indicate the presence of the cutworm. Monitor crops in the spring for expanding thin or bare areas, especially on sandy hills and south-facing slopes.

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