Field Guide     Pest Management     Corn Earworm

Corn Earworm

CROPS IMPACTED: Sweet corn, tomatoes and soybeans

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Family: Noctuidae

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About Corn Earworm

Corn earworms are a major problem in late-seasons sweet corn and are one of the contributors to grade-out corn. That being said, the majority of corn is harvested before earworms cause major damage.

Reproduction and Life Cycle

Corn earworms go through 4 stages in their lifecycle. Female corn earworm moths lay eggs in May on the silks of corn, if available. Each egg is laid individually, one female has the ability to produce and lay over 100 eggs in one night, and over 1000 eggs in her lifetime. Once eggs are laid they will only take 2 to 10 days to hatch, depending on the temperature. Once they hatch into larvae, young earworms crawl from the corn silks into the ear of the corn. Feeding for several days on the silk inside the husk, they continue moving down, feeding on the kernels at the tip of the corn. After 2 to 4 weeks of feeding, the larvae become pupa. Finally, adult moths emerge from the pupae and begin to reproduce.

Corn Earworms Identification and Habitat

Identification

Adult corn earworm moths are tan in colour with a wingspan of 3.5 to 4cm. Their forewings tend to have several dark markings with one prominent, central brown dot, which is visible on the bottom of the wings and somewhat visible from the top. Earworm hind wings have a darker brown border and are pale in colour. The female moths produce eggs that are round with the same diameter and colour of corn silk. The worms get to about 1.5 inches long with strips running length on their bodies and a tan head.

Habitat

Just as their name implies, corn earworms almost exclusively feed on the tips of sweet corn ears, leaving no visible damage to the outer husks or leaves. Most corn fields are usually harvested before economic damage has been done. However, they do venture into many other cultivated crops and weeds. They have been found in soybeans and tomatoes, feeding on their fruit.

Corn Earworm Control Methods

Cultural Control

If you are looking to avoid corn earworm damage, you must plant your sweet corn as early as possible. If you harvest the corn before the middle of August, it typically has little to no corn earworms in it. They also have natural enemies such as wasps, flies, lacewings, ladybird beetles and predatory bugs that will eat earworms eggs and larvae. These insects are extremely beneficial, are naturally found in fields and are an ongoing influence keeping the pest population balanced.

Chemical Control

There are insects that can be applied every 3 to 7 days while the silks of the corn are still fresh to control corn earworms. For ideal results, base your sprays on trap counts and temperature. Due to the risk of damage, the intervals between applications are shortened as the population of earworms and the temperature increases. What insecticide you choose is very important due to the fact that corn earworms have developed resistance to insecticides in the carbamate family including Furadan and Sevin. However, they can be controled by synthetic pyrethroids. Corn earworms lay their eggs at dusk and because synthetic pyrethroids are much more effective when applied in cooler temperatures, spraying at night will provide optimal control. Finally, aim the spray nozzles at the ears of the corn to make sure that the silks are completely covered.

Latin / Alternative Corn Earworm Names

  • - Helicoverpa zea

Sources

http://www.omafra.gov.on.ca/english/crops/facts/95-065.htm

http://www.life.illinois.edu/ib/109/Insect%20rearing/corn%20earworm.html