Beginner

Scientific Name
Helicoverpa zea

Identification

• Larvae range in colour from yellowish, to green or brown, with a fine double stripe running down their backs
• The larvae are slightly larger than the European corn borer
• The larvae are usually found in the top third of the ear
• Female moths lay their eggs on corn silk

Often Confused With
European corn borer
Fall armyworm

Period of Activity
Corn earworm do not overwinter in Ontario.  They arrive from the U.S. and Mexico on trade-winds.  In southern Ontario adult moths usually appear in mid-to-late July, or earlier, depending on the season.  In eastern and northern areas, arrival occurs in mid-to-late August.  In cooler years, these areas may not experience corn earworm at all.

Earworm activity is highest in hot weather conditions.  Peak flights often occur immediately after severe thunderstorms.

Scouting Notes
Hartstack traps have been proven up to three times more effective than the traditionally used Heliothis trap.  Use one Hartstack trap per location.  If possible, arrange to have two trapping locations spread out on the farm.

Traps must be placed near freshly silking corn.  As the silks begin to dry down, move the trap to a new site.  Traps should be placed in the field by mid-July (earlier in south-western Ontario).  Replace lures every two weeks.  Corn earworm trapping is most effective if done on an individual farm basis.  Regionally-based trapping programs will not always capture localized populations.

Thresholds
Use pheromone traps to monitor corn earworm populations.  Insecticide applications are based on the number of moths caught per week and the average temperatures.

Moths per trap per week			Spray Intervals
			Daily Maximum Temperature
			< 27°C (81°F)	27°C (81°F)
1- 6			5- 7 days	>5- 7 days
7- 90			5 days	4 days
More than 90			4 days	3 days

Advanced

Scientific Name
Helicoverpa zea

Identification
The corn earworm adult is a buff or tan-coloured moth with a wingspan of 3.5 to 4 cm (1.25 to 1.5 inches).  The forewing may have several darker markings and always has a central brown dot, clearly visible on the underside of the wing and faintly visible from the top.  The hindwings are very pale in colour, with a darker brown border.  Eyes of living moths are bright green and fade to dull olive green or brown a few days after death. There is no easy way to differentiate male from female moths.

Eggs are laid individually.  Each egg is nearly spherical and about the same colour and diameter as a corn silk. 

Larvae will grow up to 3.7 cm (1 ½ in.) long, with a prominent double stripe running the length of their bodies.  They range in colour from pale or greenish-yellow to pinkish-brown.

Earworm normally feed only on the kernels of sweet corn, beginning by feeding at the tip of the ear and moving down the ear as they grow.  Feeding is almost always confined to the top third of the ear.  Fecal matter is found as large moist pellets in the silk channel and at the ear tip.

Often Confused With
European corn borer
Fall armyworm

Biology
Corn earworm do not overwinter in Ontario; they commonly overwinter on cotton and corn crops in the southern States.  In recent years overwintering earworm have been confirmed as far north as Southern Indiana.  Each spring the adults move north on trade winds.  Depending on weather patterns and the size and location of the overwintering populations, they may arrive in southern Ontario from early June to mid-August.

Female moths lay their eggs on fresh corn silks.  One female can lay up to 100 eggs per night over a 10 night period.  The eggs incubate for 2- 10 days, depending on temperature.  After hatching the small larvae travel directly down the silk channel and complete all instars feeding on the kernels, protected by the husks.  The larvae feed for 2- 4 weeks.  Sweet corn fields are generally harvested before the larvae pupate.

Corn earworm will not normally enter a second generation in Ontario, however; continued movement of fresh populations from the south will often contribute to sustained pressure throughout the late-summer and early fall.

Resistance to pyrethroid insecticides has been confirmed across North America.  Research studies indicate that due to a southern “source” of resistant corn earworm, the level of resistance experienced in the northern United States and Canada is expected to be relatively stable from year to year.

Period of Activity
Corn earworm do not overwinter in Ontario.  They arrive from the U.S. and Mexico on trade-winds.  In southwestern Ontario, adult moths usually appear in mid-to-late July, or earlier, depending on the season.  In eastern and northern areas, arrival occurs in mid-to-late August.  In cooler years, these areas may not experience corn earworm at all.

Earworm activity is highest in hot weather conditions.  Peak flights often occur immediately after severe thunderstorms.

Scouting Notes
Hartstack traps have been proven up to three times more effective than the traditionally used heliothis trap.  Use one hartstack trap per location.  Ideally, arrange to have two trapping locations spread out on the farm.

Traps must be placed near freshly silking corn.  As the silks begin to dry down, move the trap to a new site.  Traps should be placed in the field by mid-July (earlier in south-west).  Replace lures every two weeks.  Corn earworm trapping is most effective if done on an individual farm basis.  Regionally-based trapping programs will not always reflect localized populations.

Thresholds
Use pheromone traps to monitor corn earworm populations.  Insecticide applications are based on the number of moths caught per week and the average temperatures.

Moths per trap per week			Spray Intervals
			Daily Maximum Temperature
			< 27°C (81°F)	27°C (81°F)
1- 6			5- 7 days	>5- 7 days
7- 90			5 days	4 days
More than 90			4 days	3 days

Management Notes

• Sweet corn is only susceptible to corn earworm damage while the silks are green.
• Good spray coverage of the rapidly growing silks is important.
• Due to pyrethroid resistance in North American corn earworm populations, do not rely solely on pyrethroid sprays for control.
• Pyrethroid sprays break down quickly under high temperature conditions, and more frequent spray applications are required.
• Beneficial insects and biological insecticides may help to suppress corn earworm pressure in organic sweet corn.
• Since egg-laying occurs at dusk and since pyrethroids are most effective in cool temperatures, it is best to spray these in the evening.  Aim the nozzle at the ear zone and ensure that the silks are well covered.