Common cutworm

Agrotis segetum

Crop: Chilli, Cole crops, tomato, maize, radish

Why is it a problem? Larvae of the common cutworm live in the soil and cut seedlings of various crops. It is most important in chili, causing poor plant stands that require replanting. Seedling losses in Cole crops are also occasionally very high. It is the most important insect pest in maize, but losses are generally low as a proportion of the seeds planted. The soil-dwelling larvae are often noticed too late, and they are hard to treat.

Where and when is it a problem? It is mainly an issue in temperate regions. Seedlings are affected soon after transplant, when they are young and tender. Some losses in chili can occur every year across Bhutan, but serious outbreaks are rare.

IDENTIFICATION

Caterpillars are 30–40 mm long when fully grown. They are clay-colored, with faint dark lines along the sides of their body. Pupae are smooth and shiny brown. Adults are medium-sized moths (30–40 mm). Fore-wings are grey-brown with a dark brown or black kidney-shaped marking.

Common cutworm moth
Common cutworm larva

SYMPTOMS

Larvae attack the seedlings of many crops. Large cutworm larvae cut through seedlings from just above ground level. In cabbage seedlings, single leaves may also be cut off. Larvae may also feed on tubers of potatoes and other root crops in the soil and sometimes bore into cabbages. Feeding by the small, early larval stages results in very tiny, round “windowpanes,” where larvae have eaten away the upper layer of the leaf.

Cut worm larvae
Radish damaged by cut worm

Confusion with other pests: Pest animals may cut seedlings off near ground level. The nocturnal larvae normally need to be found nearby in the soil to confirm the cause of damage.

BIOLOGY

Lifecycle: Female moths lay their eggs in a series of batches, usually on the leaves and stems of weeds or crop plants. Each female can lay up to 1,000 eggs. Early instars generally remain on the foliage of host plants for a week or two before moving down into the soil, where they assume a cutworm habit. Caterpillars and adults are active at night. The moth probably overwinters in larval or pupal form. Only one generation per year is expected in Bhutan.

Dispersal: Adults fly.

When can damage be expected? This pest is probably more serious in temperate than tropical areas.

Hosts: Larvae feed on many different plant species. In Bhutan, larvae have been reported to attack seedlings of crops such as tomato, chili, Cole crops, asparagus, and maize, as well as root crops like carrot, turnip, and potatoes.

MANAGEMENT PRACTICES

Generally, cutworms are extremely difficult to control, especially in “boom years,” as by the time infestations are noticed, the susceptible larval stages are often past and damage may already be serious. The sporadic nature of the pest means that preventative treatment in most areas is futile.

Monitoring

Monitor seedling stages early in the morning for freshly cut seedlings. If damage is found, then dig in the soil to confirm the presence of caterpillars.

Effect of variety

This is unlikely, given the very wide host range of this pest.

Non-chemical management

  • Sanitation: keep fields clean of weeds, as they act as the preferred site for oviposition and food for the first larval stages.
  • Pupae and larvae can be found in the soil and should be collected and destroyed before transplantation.
  • Hand collection of larvae is quite effective for kitchen gardens and small holdings. In the morning, dig around freshly cut seedlings to locate and kill the caterpillars.
  • Deep plowing will bring larvae and pupae to the soil surface for exposure to natural enemies and the sun for desiccation.
  • Flooding of infested fields may be possible in some areas (stagnant water). After flooding, plow the field and leave it for a few days to kill pupae.
  • Mulching of transplanted beds with Artemisia (Khempa in Dzongha, Titey Pati in Nepali) proved effective in small chili plots by acting as a physical barrier. Other materials, such as straws, might also be effective.
  • A cutworm bait developed by the NPPC in the late 1990s was very effective, but adoption was low. It was made from a mix of sawdust, rice bran, malathion (optional), and molasses. If used, malathion should be applied at a rate of 2 ml per liter of water.

Chemical management

Cutworms are very difficult to kill with pesticides as the larvae live in the soil, often under dense crop foliage.

  • Seedlings of vegetables like chilli and cabbage can be dipped in a solution of Chlorpyrifos (4 ml in 1 litre of water) overnight before transplanting.

Version: NPPC 2017. Common cutworm V1.0. Bhutan Pest Factsheet. www.PestsofBhutan.nppc.gov.bt. Date produced: 14 April 2017. Contact: nppcsemtokha@gmail.com
Image acknowledgements: NPPC & MyPestGuides crops

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