Cutworms
Beginner
Scientific Name: The black cutworm, Agrotis ipsilon and dark-sided cutworm, Euxoa messoria, likely poses the greatest threat to bulb crops.
Identification
- There are several species of cutworm that can damage onion crops
- Larvae are soft and fat, and they roll up when disturbed
- Early-season cutworms attack seedlings, 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 long
Often Confused With
White Grubs
Wireworm
Period of Activity
Cutworm damage in onions and other alliums (garlic and leeks) occurs early in the season. Plants at the seedling stage are most vulnerable to cutworm losses.
Scouting Notes
When scouting for cutworms, look for clipped plants. Clipped plants are plants that have fallen over and appear to have been cut of at the soil surface by a pair of scissors.
Threshold
No thresholds established.
Advanced
There are many different species of cutworms in Ontario which attack a wide range of crops.
Scientific Name: The black cutworm, Agrotis ipsilon and dark-sided cutworm, Euxoa messoria, likely poses the greatest threat to bulb crops.
Identification
The larvae are soft and fat, and 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
Wireworm
Biology
Most of Ontario's black cutworm population gets blown in from the south each spring, arriving between late March and early May. When 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 bulb crops occurs most often in late April and early May, shortly after transplants are put out or seedlings are developing.
Scouting Notes
When scouting for cutworms, look for clipped plants. Clipped plants are plants that have fallen over and appear to have been cut of at the soil surface by a pair of scissors..
Threshold
No thresholds established.
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.
- Apply insecticides in the early evening, as the cutworms come to the surface to feed. Insecticides are more effective on moist soils.
