Cutworms

Cutworm caterpillars live in the soil and can feed at the base of plant stems, causing plants to collapse.

Cutworm - turnip moth (<EM>Agrotis segetum</EM>)

Quick facts

Common name Cutworms
Plants affected Various
Main symptoms Stem bases are eaten and plant collapse 
Caused by Caterpillars of several species of moth
Timing All year
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What are cutworms?

  • Cutworms are the caterpillars of a number of different moths who live in the soil and tend to feed at the base of plant stems. The species that most often cause damage in gardens are the turnip moth (Agrotis segetum), large yellow underwing (Noctua pronuba) and the heart and dart moth (Agrotis exclamationis)
  • The caterpillars of these moths are rather similar in appearance, growing up to 40mm long they are usually dirty greyish-brown in colour, but can be pale green or creamy-white. They have three pairs of legs at the head end and five pairs of clasping prolegs on their abdomen, although these are often concealed as cutworms usually curl up when disturbed
  • The moths lay their eggs during the summer and the caterpillars either pupate in the autumn or overwinter and complete their feeding in the following spring.

Symptoms

  • Annual plants may be killed by these caterpillars as they can girdle the stem or sever the roots at ground level
  • Cutworms also feed above ground at night whenever the weather is mild, particularly on the leaves of low-growing herbaceous plants
  • In summer cutworms can cause damage in the vegetable garden by attacking lettuce roots, potato tubers and other root vegetables. Similar damage can be caused by slugs, vine weevil, chafer grubs and voles. When plants suddenly wilt the cutworm is often easy to find beneath the affected plant.

Control

Non chemical

  • The adult moths prefer to lay eggs where there is a dense vegetation cover, and so they occur in the largest numbers in neglected areas or where turf has been dug up to make a vegetable or flower bed 
  • Cultivation of the ground can briefly expose the grubs to predators, such as birds
  • Remove larvae of pest species from soil as they are found
  • Good weed control will help reduce infestation
  • Cutworms are very vulnerable to rain or irrigation when young. Well watered vegetable plots are often free of damage
  • A warning service is used by commercial growers to apply timely irrigation
  • Crops grown beneath fleece or insect-proof mesh are less likely to be attacked

Biological Control

A mixture of nematode species for controlling caterpillars and some other vegetable pests is sold as Fruit and Vegetable Protectionand is available from some biological control suppliers. To be effective the nematodes need to be watered into moist soil while soil temperatures are in the range of 12-20ºC (54-68ºF) as soon as possible after purchase/delivery. These temperatures occur between April and September. Nematodes should be applied as soon as possible after purchase, following the suppliers’ instructions. It may be necessary to water the soil before and after application to ensure the soil is sufficiently moist for nematode activity and survival. Repeat application may be necessary.

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Biological control suppliers (Adobe Acrobat pdf document)

Chemical

There are currently no pesticides available to home gardeners or the treatment of soil pests.

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