Corn Earworm Reference Page

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corn ear worm

Corn Ear Worm Reference Page

Pest common and scientific names: Corn Ear Worm, Helicoverpa zea

Sweet Corn Only

Pest description and crop damage Corn earworm moths are about ³⁄4 inch long, robust, with a wingspan of 1 to 1¹⁄2 inches, and range from olive green to tan to dark reddish brown. Eggs are pale green at first, turning yellowish and finally gray. Young larvae are greenish with black heads and conspicuous black hairs on the body. Fully developed worms are about 1¹⁄2 inches long and range in color from pale green or pinkish to brown. Pupae are about ³⁄4 inch long and mahogany brown. They usually are found 2 to 4 inches deep in the soil.

The corn earworm may be present throughout the year but is most abundant during August and September. Larvae feed on leaves, tassels, the whorl, and within ears, but the ears are the preferred sites for corn earworm attack. Ear damage is characterized by extensive excrement at the ear tip.

Young larvae feed on corn silks, clipping them off. Shortly thereafter, they feed their way into the ear where they remain, feeding in the tip area until they exit to pupate in the soil. First generation larvae may feed as “budworms,” damaging leaf whorls and newly forming ears (in Columbia Basin area).

Biology and life history The corn earworm overwinters as a pupa in the soil except in some areas in the north, where it is unable to survive the winter. Adults emerge in late May and June and begin laying eggs on suitable hosts. Egg laying occurs throughout the sweet corn growing year. Corn earworm moths are most active during evening and night.

Although eggs are deposited on the foliage, fresh corn silk is the favorite site for egg deposition. Female moths lay their eggs singly. Eggs are white at first but develop a dark red or brown ring within 24 hours. Eggs hatch in 5 to 7 days. Larvae feed for 2 to 3 weeks before pupating in the soil. Adults emerge in about 2 weeks and lay eggs on corn silk or developing fruits. Moths move northward and establish infestations in areas where they cannot overwinter.

The summer generations overlap, resulting in a regular and gradual build-up of the corn earworm population from the beginning to the end of the year. There are two to three generations each year.

Scouting and thresholds Moths can be sampled with pheromones placed in inverted cone-type traps. A first application of insecticide is made at first silk regardless of moth counts. The presence of five to ten moths per night per trap may be considered a tentative action threshold for additional sprays.

In fresh market corn, there is very little acceptance of earworms. Sweet corn for processing rarely is sprayed unless outbreaks are early and intense (20 to 30 moths per trap per day) at first silk.

Once larvae enter the corn ears, control with insecticides is very difficult. It depends on proper timing and thorough coverage. Begin sampling at first visible silk. The presence of large numbers of eggs on fresh corn silks indicates the potential for damaging populations. Begin treatments during silking stage, at the start of egg hatch. Direct insecticidal control towards young larvae that are feeding on the exposed ear tips.

Management—biological control

Many predators and parasites attack corn earworm eggs, including several species of Trichogramma . Most parasitized eggs turn black, but there may be a lag period before they do so. Commercial releases of Trichogramma wasps have been used with mixed results. Generalist predators such as lacewings, minute pirate bugs, and damsel bugs feed on corn earworm eggs and small larvae.

Management—cultural control

In sweet corn, very early plantings require fewer treatments than late-year corn, because earworm population densities increase as the year progresses.

Management—chemical control

1. carbaryl (Sevin) at 1 to 2 lb ai/a. PHI 2 days for harvest of ears, 14 days for forage, 48 days for fodder. REI 12 hr. Do not exceed 16 lb ai/a per crop. There are time restrictions in eastern. Washington for using carbaryl on corn. Check the Washington Department of Agriculture regulations for your area. Warning : Never apply carbaryl (Sevin) dust to pollen-shedding corn because of severe hazard to pollinating bees. Toxic to aquatic habitats . Latex-based formulations, such as Sevin XLR Plus, are less hazardous to bees.

2. chlorpyrifos (Lorsban) at 0.75 to 1 lb ai/a. PHI 35 days for ears, 14 days for grazing or silage, and 35 days for fodder. REI 24 hr. Postemergence broadcast or sprinkler application. Do not exceed 3 lb ai/a per season. Consult label for application details. Toxic to fish .

3. cyfluthrin (Baythroid) at 0.025 to 0.044 lb ai/a. PHI 0 days. REI 12 hr. Do not exceed 0.44 lb ai/a per season. Toxic to fish.

4. deltamethrin (Decis) at 0.018 to 0.028 lb ai/a. PHI 1 day for ears, grazing, or feed, and 21 days for stover. REI 12 hr. Do not exceed 0.45 lb ai/a per season. Toxic to bees.

5. endosulfan (Thiodan) at 1.5 lb ai/a. PHI 1 day. REI 48 hr. Fresh market only. Do not exceed 5 applications. For fresh market only. Do not graze or harvest for feed. Do not apply within 300 ft of aquatic habitat.

6. esfenvalerate (Asana) at 0.03 to 0.05 lb ai/a. PHI 21 days. REI 12 hr. Do not exceed 0.5 lb ai/a per year. Do not apply within 25 ft of an aquatic habitat, or within 150 ft of one when applied from the air. Toxic to fish.

7. HZNPV (Gemstar LC) at 300 ml/a (formulated product). REI 4 hr. Biological control agent. Use non-chlorinated water at a pH near 7.0 in the spray tank mix.

8. lambda-cyhalothrin (Warrior) at 0.015 to 0.025 lb ai/a. Harvest, feed and application restrictions; see label. PHI 1 day. REI 24 hr. Do not exceed 0.48 lb ai/a per year. Do not apply within 25 ft of an aquatic habitat, or within 150 ft of one when applied from the air. Toxic to fish.

9. methomyl (Lannate) at 0.23 to 0.45 lb ai/a. PHI 0 days for ears, 3 days for forage, and 21 days for stover. REI 48 hr. Do not exceed 6.3 lb ai/a per season.

10. methyl parathion (Penncap-M) at 0.75 lb ai/a. PHI 4 to 5 days for sweet corn, or 12 days for grazing and forage. REI 4 days, or 5 days where annual rainfall is less than 25 inches. See label. Do not exceed 3 lb ai/a per season.
Warning : Never spray microencapsulated methyl parathion on pollen-shedding corn,adjacent fields, or on blooming weeds at field edges and in adjacent fields. If misused, this formulation is especially hazardous to honey bees and other pollinating insects because of its strong tendency to contaminate pollen.

11. permethrin (Ambush, Pounce) at 0.1 to 0.2 lb ai/a. PHI 1 day. REI 12 hr. Do not exceed 1.2 lb ai/a per year. Toxic to fish.

12. spinosad (Spintor, Success) at 0.047 to 0.094 lb ai/a. PHI 1 day for ears, 7 days for forage. REI 4 hr. Treat eggs at hatch and small larvae. Do not exceed 0.45 lb ai/a per crop. Spinosad takes several days to achieve full effect. Monitor fields and pest populations carefully. Multiple applications may be necessary.

13. thiodicarb (Larvin) at 0.5 to 0.75 lb ai/a. PHI 0 days. REI 48 hr. Do not exceed 7.5 lb ai/a per season. Do not graze or feed corn silage or fodder.

14. zeta-cypermethrin (Mustang) at 0.035 to 0.05 lb ai/a. PHI 3 days for ears or grazing. REI 12 hr. Retreatment interval—7 days. Do not exceed 0.3 lb ai/a per season. Do not apply within 25 ft of an aquatic habitat, or within 150 ft of one when applied from the air.

Sweet Corn Seed Only
ID photos: fact page (pdf):

Pest description and crop damage Large green, brownish, or reddish worms that feed on silk and kernels of the ear.

Management—chemical control

1. azadirachtin (Neemix 4.5) at 0.02 to 0.04 lb ai/a. PHI 0 days. Begin applications at first sign of infestation. Multiple applications and thorough coverage are necessary for effective control. This botanical pesticide acts slowly. Spray early, well before harvest, and check for effect.

2. Capture 2E (bifenthrin. Apply as a foliar spray at 2.6 to 6.4 fl oz/a; do not exceed 19.2 fl oz/a per season. Highly toxic to bees. Extremely toxic to fish an aquatic invertebrates. REI 1 day.

3. chlorpyrifos (Lorsban 4E) at 0.75 to 1 lb ai/a. If crop residue is to be fed to livestock, PHI 14 days for grazing or silage, or 35 days for fodder.

4. cyfluthrin (Baythroid) at 0.025 to 0.044 lb ai/a. PHI 0 days for green forage, 21 days for grain or fodder. Do not exceed four applications or 0.175 lb ai/a per season. REI 12 hr. Do not apply within 25 ft of an aquatic habitat, within 150 ft of one when applied from the air, or within 450 ft when using a ULV.

5. cyhalothrin (Warrior) at 0.015 to 0.025 lb ai/a. PHI 21 days. Do not exceed 0.12 lb ai/a per season.

6. esfenvalerate (Asana) at 0.03 to 0.05 lb ai/a. PHI 21 days. Do not exceed 0.25 lb ai/a per season. For both sweet and field corn seed crop.

7. permethrin (Ambush) at 0.1 to 0.2 lb ai/a. PHI 0 for forage harvest, 30 days for grain or fodder. Do not exceed 0.6 lb ai/a per season. Do not make treatments less than 6 days apart. Use only before brown silk formation.

8. spinosad (Success) at 0.05 to 0.09 lb ai/a. PHI 1 day for grain harvest; 7 days for forage harvest. Do not exceed 0.45 lb ai/a per year (0.188 lb ai/a per year if used for livestock feed). This botanical pesticide acts slowly. Spray early, well before harvest, and check for effect.

Field and Silage Corn Only

ID photos: fact page (pdf):

Pest description and crop damage Large green, brown, or yellow worms that feed within silk and ears. First-generation larvae may feed as “bud worms,” damaging leaf whorls and newly forming ears.

Management—chemical control

1. bifenthrin (Capture 2EC) at 0.03 to 0.1 lb ai/a. PHI 30 days for harvest, grazing, or cutting for feed. REI 12 hr. Do not apply more than 0.3 lb ai/a per season. Do not apply on the ground within 25 ft of an aquatic habitat, or within 150 ft of one when applied from the air. ULV not permitted.

2. carbaryl at 1 to 2 lb ai/a. PHI 14 days of forage or silage grazing, and 48 days of grain harvest. REI 12 hr. Do not exceed four applications or 8 lb ai/a per season. Warning : Do not use carbaryl in areas where bees are active. Latex-based formulations, such as Sevin XLR Plus, are least hazardous to bees.

3. chlorpyrifos (Lorsban 4E) at 0.75 to 1 lb ai/a. PHI 35 days for grain harvest or corn fodder and 14 days for grazing or silage harvest. REI 24 hr. Apply as a broadcast spray. Do not exceed 7.5 lb ai/a per season. Warning: Do not use Lorsban in areas where bees are active.

4. cyfluthrin (Baythroid) at 0.0125 to 0.022 lb ai/a. PHI 0 days for green forage and 21 days for grain or fodder. REI 12 hr. Do not exceed four applications or 0.175 lb ai/a per season. Do not apply within 25 ft of an aquatic habitat, within 150 ft of one when applied from the air, or within 450 ft when using a ULV.

5. deltamethrin 1.5 EC (Decis, Delta Gold) at at 0.018 to 0.022 lb ai/a. PHI 21 days for grain or fodder, or 12 days for forage or grazing. REI 12 hr. Do not apply more than 0.095 lb ai/a per season.

6. esfenvalerate (Asana) at 0.03 to 0.05 lb ai/a. PHI 21 days. Do not exceed 0.25 lb ai/a per season.

7. gamma cyhalothrin 0.5EC (Proaxis) at 0.01to 0.015 lb ai/a. Effective prior to larvae entering the ear only. PHI 1 day for grazing and forage, or 21 days for fodder and ensilage. REI 24 hr.

8. HZNPV (Gemstar LC)—Insecticidal virus product.

9. lambda-cyhalothrin (Warrior T) at 0.015 to 0.025 lb ai/a. PHI 1 day for grazing or corn forage or 21 days of grain harvest or cutting for fodder or silage. REI 12 hr. Do not apply more than 0.12 lb ai/a per season, 0.06 lb ai/a after silk initiation, or 0.03 lb ai/a after milk stage. Do not apply within 25 ft of an aquatic habitat, or within 150 ft of one when applied from the air.

10. methomyl (Lannate) at 0.22 to 0.45 lb ai/a. PHI 21 days for harvest ears, 3 days for forage, 21 days for fodder. Do not exceed 2.25 lb ai/a or 10 treatments per season. REI 48 hr. Do not apply within 25 ft of an aquatic habitat, within 100 ft of one when applied from the air, or within 450 ft when using a ULV.

11. methyl parathion 4EC at 0.25 lb ai/a. REI 48 hr. PHI 12 days.

12. permethrin (Ambush, Pounce) at 0.1 to 0.2 lb ai/a. PHI 0 days for forage; 30 days for grain harvest or fodder. REI 12 hr. Allow 6 days between treatments. Do not apply more than 0.6 lb ai/a per season.

13. spinosad (Success) at 0.05 to 0.094 lb ai/a. PHI 7 days of forage harvest or 28 days of grain or fodder harvest. REI 4 hr. Do not exceed 0.19 lb ai/a per season.

14. zeta-cypermethrin (Mustang) at 0.022 to 0.05 lb ai/a. PHI 30 days for grain and stover and 60 days for forage. Do not exceed 0.2 lb ai/a per season. REI 12 hr. Do not apply within 25 ft of an aquatic habitat, within 150 ft of one when applied from the air, or within 450 ft when using a ULV.

Source: 2007 Pacific Northwest Insect Management Handbook

Integrated Pest Management Information Links
Insect Identification - U of Idaho
UC Pest Management Guidelines

7/18/07-jn