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Ministry of Agriculture, Food and Rural Affairs

Black Cutworm (and other early season cutworms)

Black Cutworm Black Cutworm Clipping of Tomato Transplants by Black Cutworms Black Cutworm Underside of Black Cutworm Black Cutworm Pupa Black Cutworm Moth Click to enlarge.

Beginner

Scientific Name
Agrotis ipsilon (black cutworm)

Identification

  • Larvae are soft and fat, and roll up when disturbed
  • Early season cutworms feed on the stems around the soil line, often cutting the transplant off
  • Affected plants wilt and die

Often Confused With
N/A

Period of Activity
The time for concern is when transplants are young and small.

Scouting Notes
Focus on field edges and in damp or weedy areas.  Once the characteristic symptoms of cut plants are observed, dig around these plants in the soil to a depth of about 5 cm (2 in.) to find the cutworms.

Thresholds
The control guideline is 5% damaged plants.

 

Advanced

Scientific Name
Agrotis ipsilon (black cutworm)

Identification
The larvae are soft and fat, and they roll up when disturbed.  Early season cutworms feed on the stems around the soil line, often cutting the transplant off.  Affected transplants wilt and die.  A single larvae may destroy several seedlings.

  • Black cutworm larvae are grey to black with no striping on the body and a greasy appearance.

Often Confused With
N/A

Biology
Cutworms overwinter as eggs, larvae, pupae or adult moths depending upon the species.  Not all cutworm species overwinter in Ontario during normal winters.

The majority of cutworm damage occurs to seedling vegetables early in the season and when plants are small.  Black cutworm moths do not usually overwinter in Ontario.  The adult moths are carried north on weather fronts in the early spring.  Moths are attracted to patches of vegetation for egg laying. The larvae hatch to feed on plants. Cutworms are more frequent in fields with green cover early in the spring before primary tillage. 

Period of Activity
The time for concern is when transplants are young and small.

Scouting Notes
Focus on field edges and in damp or weedy areas.  Once the characteristic symptoms of cut plants are observed, dig around these plants in the soil to a depth of about 5 cm (2 in.) to find the cutworms.  Monitoring weedy areas and neighbouring fields, as well as fall weed flushes, may also be helpful in predicting where cutworm problems may occur the following season.

Thresholds
The control guideline is 5% damaged plants.

Management Notes

  • Migrating female moths are attracted to weedy fields in the early spring for egg-laying.
  • Fields that had large weed populations, especially grasses and chickweed, may experience more cutworm problems the following season.
  • Crop rotation is also a helpful management tool.
  • Treatment with insecticides is only effective if the larvae are very small (under 2.5 cm, 1 in.) and soil conditions are favourable.
  • At more mature stages (> 2.5 cm or 1 in. in length), they cease feeding and prepare to pupate, and control becomes unnecessary.
  • If damage is isolated to a small patch or field border area, spot treatments are recommended.  In many cases the level of damage is not high enough to warrant insecticide treatments.
  • Apply insecticide treatments late in the day.
  • Insecticides are more effective on moist soils.