Cutworms

Identification

The description cutworm is applied to the larvae of a group of agricultural and horticultural crop pests of which the majority of species are in the noctuid family of moths. The term has been derived from the description of the damage caused by the caterpillars which ‘cut’ through the stems of the developing plants at or just below ground level.

The larvae are often grey, green or brown (and occasionally can appear almost white) and often with longitudinal stripes along the body. These are true caterpillars with 3 pairs of legs (and 5 pairs of prolegs) which distinguishes them from leatherjackets which are legless. Cutworms are large and depending on species, can grow to lengths of 4 – 5 cms. The caterpillars and adults are both active at night.

The adults have a wingspan of around 4 cm and are predominantly brown in colour with black markings and the rear wings are much lighter in colour than the forewings. The most damaging UK species is the Turnip moth Agrotis segetum. When disturbed the larvae will often curl into a ‘C’ shape.

Symptoms

Cutworms live in the top few centimeters of soil and feed on developing plants, roots and tubers of a wide range of crops including potatoes. They have been known to work their way along a row of plants leaving a trail of devastation. Damage to sugar beet plants is similar to that caused by leatherjackets.

Life-cycle

Adults emerge from pupae in the soil in mid-summer and lay eggs in batches of 30-50 on the leaves and stems of host plants. Eggs hatch around 2 weeks later. At first the caterpillars feed on the leaves and shoots of host plants and then migrate to live in the soil. After a period of around 2 months, and when fully fed, the larvae pupate. They can produce a second generation which emerges later in the autumn. The caterpillars from this second generation overwinter in the soil and feed on plants and roots during mild spells.

Importance

Most species of noctuid moths are widespread throughout the UK. The cutworms move through the upper layers of the soil and eat their way through young sugar beet seedlings resulting in total plant loss. Damage to established plants is less severe.

Threshold

None established.

Agrotis segetum, turnip moth adult

Cutworm caterpillar

Cutworm pupae