ADLib Glossary (C)

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Cutworms

Cutworm is a name given to the caterpillars of the turnip moth which is widespread in the UK, often overwintering on weedy land.

Adult moths emerge in late May and lay their eggs on vegetation, both weeds and crops (including potatoes, beet, lettuce and leeks).

The caterpillars hatch in 1 - 3 weeks depending on temperature and conditions and begin to feed on leaves. At this stage heavy rainfall or irrigation will help wash young caterpillars off of the leaves on to wet soil where they often die.

After around 2 weeks feeding on the foliage, caterpillars will descend to the soil and begin feeding at or below soil level. This has the effect of seriously weakening plants and on potatoes tubers can be seriously damaged. In severe cases 10% of potatoes can be lost or damaged resulting in financial loss. Feeding takes place after dark.

The degree of risk is influenced by:

  • Soil Type: In crops in light to medium soil including peats are more likely to suffer infestation particularly in long, dry summers.
  • Crops planted immediately after heavy weed cover are also high risk.
  • Unirrigated crops tend to be more at risk because heavy water-flow washes leaves clean.

Cutworm attacks can be controlled by:

  • Using monitoring and forecasting services e.g. that run by ADAS - forewarned is forearmed.
  • Insecticides approved for cutworm control include chlorpyrifos and several pyrethroids but only spray when a significant risk has been identified.
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