Cutworms

Damage

Okra seedling damaged by cutworm caterpillar (right). Note healthy seedling on the left. Close-up of cutworm (inset)

© A.M. Varela, icipe

Host Range

Cutworms attack cultivated plants belonging to more than 15 families. Common host plants include okra, cabbage, cauliflower, rutabaga, bell pepper, tomato, potato, maize and cotton. 
 

Symptoms

External feeding on leaves by young caterpillars results in the presence of very tiny round 'window panes'. Feeding on leaves, stalks and stems results in falling leaves, small holes in the stems or cut stems respectively. Feeding on tubers and roots results in a variety of holes, ranging from small and superficial to very large deep ones. 

Feeding by medium to large caterpillars is easier to recognise because whole leaves may fall off the plant after being cut through at the base of the stalk. Alternatively, small holes may be found on the stems and roots at the soil surface. A further sign of their activity is the presence of leaf pieces partly pulled down into the soil. 

The activity of the fully-grown caterpillars is very obvious. Whole plants fall over and on root crops deep holes become visible at and above the soil surface. Damage to underground tubers (e.g. potatoes) may be difficult to recognise before harvest. 
Damage is far more severe under very dry conditions and occurs deeper below the surface (Thygesen, 1971; Esbjerg, 1990). 
 

Affected Plant Stages

Seedling stage and vegetative growing stage.
 

Affected Plant Parts

Leaves, roots and stems.
 

Symptoms by affected plant part:

Leaves: "windowpane" holes on leaves; abnormal leaf fall.
Roots: Holes ranging from small and superficial to very large deep ones. 
 

The eggs are ribbed, globular and small (about 0.5 mm in diameter). When newly laid they are cream coloured turning reddish-yellow to blackish before hatching. Eggs are laid singly or in small groups on moist soil, on weeds or on the stem and lower leaves of host plants or on low growing vegetation. A single female may lay up to 2000 eggs. Preferred substrates are densely growing plants relatively low to the ground and fine-textured plant debris in untilled fields. Damp, low-lying areas within untilled fields are particularly attractive for egg-laying moths. Eggs hatch in 10 to 28 days. 

Young caterpillars are pale, yellowish-green with a blackish head. Older caterpillars have a plump body; their colour varies from grey, dark green to brown or black with shiny, greasy-looking skin. Fully-grown caterpillars are 4 to 5 cm long. Newly hatched caterpillars feed on the leaves and later on the stems. 

Older caterpillars feed at the base of plants or on roots or stems underground. They are nocturnal and hide in the soil or under stones and plant debris during the day. At night they move up to the soil surface to feed. Caterpillars construct burrows or tunnels in the soil about 2.5 to 5 cm deep near the host plant. They pupate in an earthen cell in the soil. 

The pupa are about 1.7 to 2.5 cm long, smooth and shiny reddish-brown with two dark spines at the tip of the abdomen. They appear almost black in colour just before the moth emerges.

The adult is a medium-sized moth, about 2 cm long with a wingspan of 4 to 4.5 cm. The forewings are greyish-brown with black lines or kidney-shaped markings along the side margins. The hindwings are pearly white with dark brownish margins and veins. They are active at night.

The life cycle can be completed in 6 weeks under warm conditions.

Cutworm (Agrotis sp.) Early instars are about 7-12 mm long. Fully grown caterpillars are 35-50 mm long.

© A.M. Varela, icipe

Black cutworm (Agrotis ipsilon). Pupae are brown to dark brown and approximately 1.7 to 2.5 cm in length and 5 mm in width.

© Courtesy EcoPort (http://www.ecoport.org): P. Ooi

Turnip moth (Agrotis segetum). The adult moth is about 2 cm long and has a wingspan of 4 to 4.5 cm.

© Courtesy EcoPort (http://www.ecoport.org): P. Ooi

Pest and disease Management: General illustration of the concept of Infonet-biovision

This illustration shows the methods promoted on infonet-biovision. The methods shown at the top have a long-term effect, while methods shown at the bottom have a short-term effect. In organic farming systems, methods with a long-term effect are the basis of crop production and should be used of preference. On the other hand methods with a short-term effect should be used in emergencies only. On infonet we do not promote synthetic pesticides. 

Further below you find concrete preventive and curative methods against Cutworms.

Cultural practices

• Ploughing exposes caterpillars to predators and to desiccation by the sun.
• Fields should be prepared and vegetation and weeds destroyed 10 to 14 days before planting the crop in the field. If the field is planted soon after land preparation some cutworms may be alive and attack the new crop.
• Delaying transplanting slightly until the stems are too wide for the cutworm to encircle and/or too hard for it to cut may reduce cutworm damage.
  Hand picking of caterpillars at night by torch or very early morning before they return into the soil is useful at the beginning of the infestation.
• Flooding of the field for a few days before sowing or transplanting can help kill cutworm caterpillars in the soil.

Natural enemies