Bayer CropScience - Pestspotter

Pest: Cutworm

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.

The most damaging UK species is the Turnip moth Agrotis segetum. 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. 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 behind them.

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 two 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 two 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. In hot dry conditions the caterpillars feed directly on the developing potato tubers rendering the affected tubers unmarketable which increases sorting costs.

Irrigation to keep soils moist during hot weather can help reduce damage.

Threshold
None established

If cutworm larvae are knocked from theleaves before they are ready to move intothe soil they cannot re-climb the plant and die. About 10 mm of heavy rain is considered to be sufficient to kill most larvae on the leaf. Irrigation can therefore be used as an alternative to insecticides.