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Beginner

Scientific Name
Agrotis ipsilon

Identification
Larvae. Black cutworm larvae vary in size from 3 mm when newly hatched to 4-5 cm when fully grown. Their color ranges from grey to nearly black with a greasy, pebbly skin. There is a pale rather indistinct narrow stripe along the center of the back. When disturbed, the larvae typically curls up into a C-shape.

Adult moth. The moths are relatively large compared to other cutworm species and have wingspans of 40-50 mm. They are brownish-grey with a light silvery band on the wings. Their forewings have small but distinct black dagger-like markings that look like cherries.

Often Confused With
Variegated cutworm
Fall armyworm

Period of Activity
Two generations attack potatoes in Ontario

Larvae of the first generation are active from April until June. They feed on foliage and cut off stems of small plants at ground level. The larvae may be found by removing soil to a depth of 5 cm from around damaged plants.

The second generation larvae are active from mid-July until August. The large instars of this second generation chew holes in tubers.

Scouting Notes

Spring:
Walk fields shortly after emergence. Look for small shotgun holes in the leaves, wilted stems or stems cut off at ground level. The larvae may be found by removing soil from around damaged plants to a depth of about 5 cm.

Scout in the evening to find larvae actively feeding

Check 20 plants in 5 areas of the field. Always check low spots and weedy areas. Tentative threshold is 5% affected plants.

Mid Season:
Usually larvae of the second generation attacks potatoes from mid-July until the end of August

Pheromone traps should be used to monitor flights of male moths. Hang the traps 1.8-2.1 m above the ground close to trees or shrubs surrounding the fields. Do not hang traps near lights that are on at night. Check the traps daily to determine if there were flights the previous night. Remove captured male moths daily from the traps, and change the sticky surfaces every 2 weeks.

A high number of male moths caught in traps indicate that the moths are mating and that the females are laying eggs. Growers have 10-12 days to apply an insecticide to control small larvae. Large larvae cannot be controlled because they usually feed on tubers and remain underground.

Thresholds

1. For spring scouting (first generation), the tentative threshold is 5% affected plants.
2. For second generation:

Tentative Thresholds for the second generation of black cutworm using pheromone traps*

Trap catches	Potential for cutworm damage
9 to 15 moths in a 7-day period	Moderate to high
5 per night for at least 2 consecutive nights	High

*These thresholds are being evaluated in Ontario. They appear to be reliable.

An insecticide application is recommended no later than 10 days after peak moth activity.

Advanced

Scientific Name
Agrotis ipsilon

Identification
Larvae. Black cutworm larvae vary in size from 3 mm when newly hatched to 4-5 cm when fully grown. Their color ranges from grey to nearly black with a greasy, pebbly skin. There is a pale rather indistinct narrow stripe along the center of the back. When disturbed, the larvae typically curls up into a C-shape.

Adult moth. The moths are relatively large compared to other cutworm species and have wingspans of 40-50 mm. They are brownish-grey with a light silvery band on the wings. Their forewings have small but distinct black dagger-like markings that look like cherries.

Often Confused With
Variegated cutworm
Fall armyworm

Biology
Life stages: eggs, larvae, pupae, adult moths.

Female moths lay eggs in groups on grasses, dense patches of weeds and on plant debris.  The lower areas of potato fields are the preferred spots for female moths to lay their eggs. After egg hatching, larvae go through 6 molts before turning into pupae in the soil. The small larvae, instars 1 to 3, chew what look like shot holes in the leaves. The larger larvae, instars 4 to 6, cut off stems. It is this larger larva that can chew holes in potato tubers.  Black cutworm larvae are loners and feed in the evening or at night and spend the day curled up in the soil.

Black cutworm problems are usually spotty in a field and concentrated in low, weedy areas.

The black cutworm does not overwinter in Ontario. In the spring, the adult moths can be blown long distances in storms along the low level jet stream. The first appearance of moths in Ontario is usually in mid-April. 

Black cutworm infestations in potato fields are unpredictable, and damage varies from field to field and from year to year. If not detected, this insect can cause considerable economic losses, so scouting is essential.

Period of Activity
Two generations attack potatoes in Ontario

Larvae of the first generation are active from April until June. They feed on foliage and cut off stems of small plants at ground level. The larvae may be found by removing soil to a depth of 5 cm from around damaged plants.

The second generation larvae are active from mid-July until August. The large instars of this second generation chew holes in tubers.

Scouting Notes

Spring:
Walk fields shortly after emergence. Look for small shotgun holes in the leaves, wilted stems or stems cut off at ground level. The larvae may be found by removing soil from around damaged plants to a depth of about 5 cm.

Scout in the evening to find larvae actively feeding.

Check 20 plants in 5 areas of the field. Always check low spots and weedy areas. Tentative threshold is 5% affected plants.

Mid Season:
Usually larvae of the second generation attacks potatoes from mid-July until the end of August

Pheromone traps should be used to monitor flights of male moths. Hang the traps 1.8-2.1 m above the ground close to trees or shrubs surrounding the fields. Do not hang traps near lights that are on at night. Check the traps daily to determine if there were flights the previous night. Remove captured male moths daily from the traps, and change the sticky surfaces every 2 weeks.

A high number of male moths caught in traps indicate that the moths are mating and that the females are laying eggs. Growers have 10-12 days to apply an insecticide to control small larvae. Large larvae cannot be controlled because they usually feed on tubers and remain underground.

Thresholds

1. For spring scouting (first generation), the tentative threshold is 5% affected plants.
2. For second generation:

Tentative Thresholds for the second generation of black cutworm using pheromone traps*

Trap catches	Potential for cutworm damage
9 to 15 moths in a 7-day period	Moderate to high
5 per night for at least 2 consecutive nights	High

*These thresholds are being evaluated in Ontario. They appear to be reliable.

An insecticide application is recommended no later than 10 days after peak moth activity.

Management Notes
Control weeds. The moths are attracted to weedy spots on low areas of fields for egg laying.

Black cutworm infestations are sporadic and unpredictable. If field monitoring indicates that population are at threshold levels, apply a registered foliar insecticide. Sprays should be done in the evening.