Beginner

Scientific Name
Trichoplusia ni

There are 3 major caterpillar pests of crucifer crops in Ontario. The imported cabbageworm (ICW), the cabbage looper (CL), and the diamondback moth (DBM).  

Identification

• Adult CL are mottled greyish-brown moths with a silvery figure eight pattern on their forewings 
  
• Adult females lay several hundred small, rounded, white eggs, usually in small groups on the underside of leaves
  
• Larvae are light green with a white stripe along each side of the body and two faint lines down the middle of the back
  
• Caterpillars move in distinctive looping manner as legs are confined to front and rear of the body
  
• Pupa, in a loose cocoon on the underside of the leaf, darken in color as they mature

Often Confused With
Imported cabbageworm
Diamondback moth

Period of Activity
Depending upon temperatures and wind patterns, CL adults arrive in Ontario from midsummer to fall. There may be 1- 2 generations in southern Ontario depending upon the time of arrival and temperatures during August and September.

Scouting Notes
To monitor, count CL larvae on at least 25 randomly selected plants throughout the field by scanning both sides of leaves and pulling back loose wrapper leaves. Fresh feeding damage and frass are good signs that large larvae are present. Choose 5 sites in each block, examining 5 plants at each site. Be sure to include 2 perimeter areas.  There are two ways to quantify CL infestations, using Cabbage Looper Equivalents (CLE) or Percentage Infestation.   

Thresholds

Advanced

Scientific Name
Trichoplusia ni

There are 3 major caterpillar pests of crucifer crops in Ontario: the imported cabbageworm (ICW), Pieris rapae (L.), the cabbage looper (CL), Trichoplusia ni (Hubner) and the diamondback moth (DBM), Plutella xylostella (L.). The CL is one of the most destructive pests of crucifers in Ontario.  Its presence is virtually unpredictable and it may show up in one field and not in the adjacent field.  CL do not overwinter in Ontario, but migrate in from the south.

Identification
Adult CL are mottled greyish-brown moths have a distinctive silvery figure eight pattern on their forewings and a slight tuft of hair behind the head with a wingspan of about 3.8 cm (1 ½ in.). Eggs are small, rounded and greenish-white, usually in small groups on the underside margins of leaves. CL larvae are light green with a white strip along each side of the body and two faint lines down the middle of the back.  Since their legs are confined to the front and rear of the body, they move in a very distinctive “looping” manner, which can be used to distinguish them from the imported cabbage worm and the diamondback moth. At maturity, CL larvae are about 4 cm (1 ½ in.) long. The pupa is initially light green in a loose cocoon, darkening in color as it matures.

Small CL larvae generally feed on the underside of leaves, while more mature larvae chew large, irregular holes throughout the plant. Large amounts of dark, brown-green frass can also stain cauliflower heads and make cabbage and broccoli unmarketable. Unlike the imported cabbageworm, CL larvae deposit frass in piles of more than 3 pellets.

Often Confused With
Imported cabbageworm
Diamondback moth

Biology
The adult CL moth is generally nocturnal, but can sometimes be found resting on the underside of cabbage leaves during the day. Adult female CL lay several hundred small, rounded, white eggs, usually in small groups on the underside margins of leaves.  Larvae hatch after 3- 4 days and begin feeding on the foliage, heads or florets. During this feeding time, the larvae develop through 5 instars in 2- 3 weeks.  After such time, CL larvae pupate in webbed cocoons often on the underside of the host plants. This stage lasts about 2 weeks.

Period of Activity
Depending upon temperatures and wind patterns, CL adults arrive in Ontario in midsummer to early fall. After eggs are laid, larvae hatch in 3– 4 days and begin feeding. The larvae mature in about 2 weeks and pupate. The pupal stage lasts about 2– 3 weeks and adult moths emerge. There may be 1–2 generations in southern Ontario depending upon the time of arrival and temperatures during August and September.

Scouting Notes
To monitor, count CL larvae on at least 25 randomly selected plants throughout the field by scanning both sides of leaves and pulling back loose wrapper leaves. Fresh feeding damage and frass are good signs that large larvae are present. Choose 5 sites in each block, examining 5 plants at each site. Be sure to include 2 perimeter areas. There are two ways to quantify CL infestations, using Cabbage Looper Equivalents (CLE) or Percentage Infestation.

Thresholds

Management Notes

• Small caterpillars are always easier to control. Monitor early!
• Caterpillars feeding directly on the heads or growing points are a more serious threat than those feeding on the outer leaves.
• When plants are small, damage has a more profound effect on yield and head size. With that said, caterpillar control is more critical just before harvest because of feeding damage and the presence of frass.