Cut worms

The different types of cutworm are; turnip moth, greasy cutworm, black cutworm and tobacco cutworm. They mainly affect plants like; beans, cabbage, kales, Brassicas, carrot, cotton, eggplant, maize, peas, peppers, pigeon pea, potato, sesame, cauliflower, bell pepper, sorghum, tea and tomatoes. The cutworms mainly affect the vegetative stage and seedling stage.

Damage: The young cutworm caterpillars normally feed on leaves and later on the stems. When they mature, they tend to cause the most damage by eating and destroying the entire plant. They first girdle and cut-off young seedlings at ground level during the night and drag into the tunnel in the soil to feed on them daytime

Damage on different plants: In beans, they feed on the leaves, buds, flowers and pods while in maize they feed on the leaves, silk and ears.  On tubers and root crops, cutworms feed on the tubers and roots boring a wide shallow hole while on thick stemmed vegetables they hollow the stem below the ground which makes the plants to wilt and die.

Signs of infestation

Sign Stage of caterpillar

·         Tiny round ‘window panes’,

·         feeding on leaves, stalks and stems results in falling leaves, small holes in the stems or cut stems

·         Feeding on tubers and roots results in a variety of holes ranging from small and superficial to very large deep ones.

 Young caterpillars
·         Whole leaves fall off the plant after being cut through at the base of the stalk

·         Small holes may be found on the stems and roots at the soil surface.

·         Presence of leaf pieces, partly pulled down into the soil.

 Medium to large caterpillars
·         Whole plants fall over

·         On root crops, deep holes become visible at and above the soil surface

·         Feed at the base of plants or on roots or stems underground.

·         They are nocturnal and hide in the soil or under stones during the day.

·         They pupate in an earthen cell in the soil

 Older caterpillars

Appearance of the cutworms at different stages

The eggs are normally cream colored turning reddish-yellow to blackish before hatching. They are ribbed, globular, small and 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 2000eggs. Damp. Low lying areas within untilled fields are particularly attractive for egg-laying moths and normally hatch in 10 to 28days.

The pupa is about 1.7 to 2.5cm long, smooth and shiny red brown with two dark spines at the tip of the abdomen.

Young caterpillars are pale, yellowish green with a blackish head

Older caterpillars have a plump body with their color varying from grey, dark green to brown or black with shiny, greasy-looking skin.

Fully-grown caterpillars are normally 4 to 5cm long.

The adult (medium-sized moth) is about 2cm long with a wingspan of 4-4.5cm. The forewings are normally greyish brown with black lines along the side margins. The hind wings are pearly white with dark brown margins and veins.

 

Adult cutworm moth

Image courtesy wisconsin horticulture

Cutworm infestation management

Cultural Practices

In order to reduce cutworm infestation it is important to practice this: Crop rotation, enhancement of soil quality, choice or resistant seed varieties, water management, monitoring/screening, field sanitation, mechanical barriers and post-harvest treatment.

 

  • Fields should be checked before sowing or transplanting.
  • When monitoring damage, count damaged and freshly cut leaves, freshly cut young plants and holes in leaves and in the stems preferably at dawn.
  • Monitoring of cutworm moths can be done using pheromone traps.
  • Bigger seedlings are more tolerant to damage
  • Ploughing is a good control measure to expose the caterpillars to predators
  • The field should be prepared and the vegetation and weeds destroyed 10-14 days prior to planting.
  • Delaying transplanting until the stems are too wide to be destroyed by the cutworms.
  • Monitoring the field at dawn or dusk and handpicking them to destroy is important during infestation.

Habitat Management

  • Wild flower strips
  • Hedgerows
  • Functional biodiversity – regulation of pests through conservation and enhancing of indigenous natural enemies
  • Introduction of predators and pathogens

 

Physical measures

  • Plant extracts
  • Natural products,
  • Pheromones
  • Insect traps and baits
  • Use of Neem
  • Protective collars
  • Ash
  • Stick
  • Sticky substances

 

 

Biological control methods 

Natural enemies: parasitic wasps, flies, ground beetles, lacewings, praying mantis, ants, birds, and hens.

Parasitods: Braconid wasp, Cotesiaspp and Tachinid fly

 

Image courtesy plant care