Cutworm
Beginner
Scientific Names
The black cutworm, Agrotis ipsilon, likely poses the greatest threat to Brassica crops.
Identification
- There are several species of cutworm
- 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
- The adult is a grey night-flying moth about 2.5 cm (1 in.) long
Often Confused With
White grubs
Wireworms
Slug damage
Period of Activity
Cutworm damage in brassica crops occurs most often in late April and early May, shortly after transplants are put out. Plants at the seedling stage are most vulnerable to cutworm losses.
Scouting Notes
Scouting is best done in the middle of the day, when the water demand of plants is high. Look for individual plants that are wilting or falling over. If such plants are found, check the base of the plant for feeding damage, and check the soil nearby for a cutworm. They usually spend the day close to the plants and within 2 or 3 cm (1 in.) of the soil surface.
Thresholds
The control guideline is 5% damaged plants.
Advanced
Scientific Names
The black cutworm, Agrotis ipsilon, likely poses the greatest threat to Brassica
There are many different species of cutworms in Ontario. They attack a wide range of crops.
Identification
The larvae are soft and fat, and they roll up when disturbed. Black cutworms feed at night, cutting off seedlings and transplants at the soil level. Most of their damage is found at the field edge or in weedy fields. One cutworm can kill several plants before it reaches full size and pupates. The adult is a grey night-flying moth about 2.5 cm (1 in.) long.
Often Confused With
White grubs
Wireworms
Slug damage
Biology
Most of Ontario's black cutworm population gets blown in from the south each spring, arriving sometime between late March and early May. Second generation larvae are active in July and August and can be damaging to rutabagas, turnips and radishes. When the moths arrive they lay their eggs on grasses and weeds. Upon hatching, the tiny larvae feed on weeds and sometimes move into the crop. Most species of cutworms feed at night, hiding during the day under loose stones or in the soil near the base of the plant.
Period of Activity
Cutworm damage in brassica crops occurs most often in late April and early May, shortly after transplants are put out. Plants at the seedling stage are most vulnerable to cutworm losses.
Scouting Notes
Scouting is best done in the middle of the day, when the water demand of plants is high. Look for individual plants that are wilting or falling over. If such plants are found, check the base of the plant for feeding damage, and check the soil nearby for a cutworm. They usually spend the day close to the plants and within 2 to 3 cm (1 in.) of the soil surface.
Thresholds
The control guideline is 5% damaged plants.
Management Notes
- Adult populations can be monitored with black light traps and/or sex pheromones; however, research has shown that light traps may underestimate early season densities and should be used cautiously.
- Migrating female moths are attracted to weedy fields in the early spring for egg-laying.
- Early-season cutworm control is most effective on small (less than 2.5 cm or 1 in.) larvae. Larger larvae are difficult to control with insecticides. At more mature stages (>2.5 cm or 1 in. in length), they cease feeding as they prepare to pupate, and control becomes unnecessary.
