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Ministry of Agriculture, Food and Rural Affairs

Cutworms

Cutworm Cutworm larvae in chickweed Cutworm damaged tomatoClick to enlarge.

Beginner

Scientific Name
Various Lepidoptera species

Identification

  • 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
White grubs
Wireworms

Period of Activity
Migrating female moths are attracted to weedy fields in the early spring for egg-laying.  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 at the seedling stage are most vulnerable to cutworm losses.

Scouting Notes
While walking fields, keep an eye open for wilted plants or stems that have been severed at the soil level.  Look for cutworm larvae in the top 2.5 cm (1 in.) of soil surrounding the damaged plant.  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, 2/5 in.) are easier to control.  Larvae greater than 2.5 cm (1 in.) in length stop feeding as they prepare to pupate.  Control of these large larvae is usually unnecessary.

Advanced

Scientific Name
Various Lepidoptera species

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

Identification
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
White grubs
Wireworms

Biology
Cutworms do not usually overwinter in Ontario.  The adult moths are carried north by the trade winds in the early spring.  Female cutworm moths are often attracted to fields with green cover (perennial weeds, fall germinating annuals, cover crops etc.) where they will lay eggs.

Period of Activity
Larval activity usually coincides with early season planting and emergence.  Most species of cutworms feed at night, hiding during the day under loose stones or in the soil near the base of the plant.

Scouting Notes
While walking fields, keep an eye open for wilted plants or stems that have been severed at the soil level.  Look for cutworm larvae in the top 2.5 cm (1 in.) of soil surrounding the damaged plant. 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 are most likely to cause a great deal of damage.  As the cutworm pass through each instar, the amount of feeding potential dramatically decreases.  Larvae longer than 2.5 cm (1 in.) 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 IN CORN
(Ohio ICM newsletter, May 1994)

LARVAL INSTAR

APPROX. SIZE

APPROX. FEEDING DAYS

cm

in.

4

<2.5

<1.0

25

5

2.5

1.0

21

6

2.5- 3.75

1.0- 1.5

14

7

3.75- 5.0

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.
  • Apply herbicides in the fall to eliminate fall germinating, annual and perennial weeds.