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Ministry of Agriculture, Food and Rural Affairs

Black Cutworms

Black Cutworm Black Cutworm Cutworm damage to transplant (tomato) Black Cutworm Underside of Black Cutworm Black Cutworm Pupa Black Cutworm Moth
Click to enlarge.

Beginner

Scientific Name
Agrotis ipsilon

Identification

  • Black cutworm larvae are greyish-black with a paler underside
  • Mature larvae are about 5 cm (2 in.) long
  • The larvae are soft and fat, and they roll up when disturbed
  • Early-season cutworms attack the seedling plants, usually cutting them below or at the soil surface
  • A single larva may destroy several seedlings

Often Confused With
Wireworm damage
Damping-off

Period of Activity
Warm, clear, calm nights in early spring are ideal for moths to lay eggs. Feeding occurs from early May through to mid-June. Larval activity usually coincides with early season planting and emergence.  Damage is often sporadic and appears in localized areas within a field. Most species of cutworms feed at night, hiding during the day under loose stones or in the soil near the base of the plant. Plants are most vulnerable to cutworm losses shortly after transplanting.

Scouting Notes
While walking fields, keep an eye open for wilted plants or stems that have been severed at the soil level.  Dig around the damaged plant to look for the cause of the damage.  If a cutworm is uncovered, take note of its size.  Record the percentage of wilted or cut plants within the field.

Thresholds
For most vegetable crops, the control guideline is 5% damaged plants. Small larvae (less than 1 cm or 3/8 in.) are easier to control. Large larvae stop feeding as they prepare to pupate.  Control of these large larvae is usually unnecessary.

Advanced

Scientific Name
Agrotis ipsilon

Several different species of cutworms can attack pepper transplants shortly after planting.  Species most commonly found in Ontario include: black cutworm, dark-sided cutworm, and the sandhill cutworm.

Cutworms feed at night and can often be found during the day hidden in the soil near the base of the damaged plants.

Identification
Black cutworm larvae are greyish-black with a paler underside. Mature larvae are about 5 cm (2 in.) long. They are soft and fat, and curl up into a C-shape when disturbed.  

The young caterpillars cut off young plants near ground level, causing them to wilt and fall over.  A single larva may destroy several seedlings.

Often Confused With
Wireworm damage
Damping-off

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

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 therefore more frequent in fields with green cover early in the spring before primary tillage.

Period of Activity
Warm, clear, calm nights in early spring are ideal for moths to lay eggs. Eggs are laid on dense vegetation, low to the ground, and are usually laid before primary tillage in the spring. Feeding occurs from early May through to mid-June. Larval activity usually coincides with early season planting and emergence.  Damage is often sporadic and appears in localized areas within a field. Most species of cutworms feed at night, hiding during the day under loose stones or in the soil near the base of the plant. Plants are most vulnerable to cutworm losses shortly after transplanting.

Scouting Notes
Scout for cutworms early in the morning or in the evening, if possible, as they are nocturnal and hide during the day. Look for wilted plants or stems that have been severed at the soil level.  Look in the soil around the base of the plant, and under plants and plant debris to find the cause of the damage.  If a cutworm is uncovered, take note of its size.  Record the percentage of wilted or cut plants within the field. Focus on field edges and in damp or weedy areas.

Thresholds
For most vegetable crops the control guideline is 5% damaged plants. Small larvae are most likely to cause a great deal of damage.  As the cutworm pass through each instar, the amount of feeding potential dramatically decreases. Large larvae stop feeding as they prepare to pupate.  Control of large larvae is unnecessary as they are no longer causing damage to the crop.

Relationship between black cutworm development & potential damage (Ohio ICM newsletter, May 1994)
Larval Instar Approx. size (inches) Approx. feeding days
4 < 1.0 25
5 1.0 21
6 1.0-1.5 14
7 1.5-2.0 5

Management Notes

  • Apply registered insecticides at night as the cutworms come up to feed.  Ensure good coverage of the plant by using high water volumes and a medium droplet size.